Publications

Below is a full list of publications by Columbia Water Center and affiliated researchers arranged by publish date. Use the quick links to search by our research themes or the tools below to search or browse these resources by category.


  • The Development of a Flash Flood Severity Index 2016-04-15
  • America’s Water: Developing a Road Map for the Future of our Nation’s Infrastructure 2016-03-31
  • Sampling of Water Courses at American Universities in 2015 2016-01-08
  • Chlorate Challenges for Water SystemsAlfredo K, Stanford B, Roberson JA, Eaton A| Journal of the American Water Works Association, 2015-04
  • CIPT Sandesh Issue 4Kamal Vatta and Romit Sen, 2015-02-27
  • CIPT Sandesh, September 2014K Vatta, R Sen | CIPT Newsletter, September 2014, 2014-09
  • Floods and climate: emerging perspectives for flood risk assessment and managementB Merz, J Aerts, K Arnbjerg-Nielsen, M Baldi, A Becker, A Bichet, G Blöschl, LM Bouwer, A Brauer, F. Cioffi, JM Delgado, M. Gocht, F Guzzetti, S Harrigan, K Hirschboeck, C Kilsby, W Kron, HH Kwon, U Lall, R Merz, K Nissen, P Salvatti, T Swierczynski, U , 2014-07-30 [+]
    Abstract. Flood estimation and flood management have traditionally been the domain of hydrologists, water resources engineers and statisticians, and disciplinary approaches abound. Dominant views have been shaped; one example is the catchment perspective: floods are formed and influenced by the interaction of local, catchment-specific characteristics, such as meteorology, topography and geology. These traditional views have been beneficial, but they have a narrow framing. In this paper we contrast traditional views with broader perspectives that are emerging from an improved understanding of the climatic context of floods. We come to the following conclusions: (1) extending the traditional system boundaries (local catchment, recent decades, hydrological/hydraulic processes) opens up exciting possibilities for better understanding and improved tools for flood risk assessment and management. (2) Statistical approaches in flood estimation need to be complemented by the search for the causal mechanisms and dominant processes in the atmosphere, catchment and river system that leave their fingerprints on flood characteristics. (3) Natural climate variability leads to time-varying flood characteristics, and this variation may be partially quantifiable and predictable, with the perspective of dynamic, climate-informed flood risk management. (4) Efforts are needed to fully account for factors that contribute to changes in all three risk components (hazard, exposure, vulnerability) and to better understand the interactions between society and floods. (5) Given the global scale and societal importance, we call for the organization of an international multidisciplinary collaboration and datasharing initiative to further understand the links between climate and flooding and to advance flood research.
  • Fluoride contamination in the Bongo District of Ghana, West Africa: geogenic contamination and cultural complexitiesKA Alfredo, DF Lawler & LE Katz | Water International, Vol. 39, Iss. 4, 2014, 2014-06-23
  • A forward modeling approach to paleoclimatic interpretation of tree-ring dataMN Evans, BK Reichert, A Kaplan, KJ Anchukaitis, EA Vaganov, MK Hughes, and MA Cane | Journal of Geophysical Research, 2014-05-10 [+]
    Abstract: We investigate the interpretation of tree-ring data using the Vaganov-Shashkin forward model of tree-ring formation. This model is derived from principles of conifer wood growth, and explicitly incorporates a nonlinear daily timescale model of the multivariate environmental controls on tree-ring growth. The model results are shown to be robust with respect to primary moisture and temperature parameter choices. When applied to the simulation of tree-ring widths from North America and Russia from the Mann et al. (1998) and Vaganov et al. (2006) data sets, the forward model produces skill on annual and decadal timescales which is about the same as that achieved using classical dendrochronological statistical modeling techniques. The forward model achieves this without site-by-site tuning as is performed in statistical modeling. The results support the interpretation of this broad-scale network of tree-ring width chronologies primarily as climate proxies for use in statistical paleoclimatic field reconstructions, and point to further applications in climate science.
  • China's water sustainability in the 21st century: a climate-informed water risk assessment covering multi-sector water demandsX. Chen, D. Naresh, L. Upmanu, Z. Hao, L. Dong, Q. Ju, J. Wang, and S. Wang, 2014-05-08
  • Climate information based streamflow and rainfall forecasts for Huai River basin using hierarchical Bayesian modelingX. Chen, Z. Hao, N. Devineni, and U. Lall, 2014-04-29
  • Assessment of trends in groundwater levels across the United StatesTess Russo, Upmanu Lall, Hui Wen, Mary Williams, 2014-03-17
  • One Water. One World. Many Climes. Many SoulsUpmanu Lall, 2014-03-14
  • Reviewing the occurrence data used in the revised Arsenic RuleKatherine Alfredo, Chad Seidel, and J. Alan Roberson, 2014-03 [+]
    Large sampling initiatives are integral to the process of developing regulations, yet best practices for the data acquisition and analysis required to quantify potential health risks posed by contaminants are not well-defined. Despite differing database sizes and analytical approaches, previous studies predicting water systems likely to be out of compliance with the maximum contaminant levels (MCLs) in the proposed revision of the Arsenic Rule were in close agreement with the predictions of the US Environmental Protection Agency’s (USEPA’s) Arsenic Occurrence and Exposure Database and the current study’s analysis of the agency’s second six-year review of enforced MCLs. The epidemiologic analyses used in the final revision of the Arsenic Rule cite the differences in proposed concentrations leading to a reduction in potential incidences of cancer; however, for this type of analysis, population-based occurrence data are necessary. When the data were analyzed on the basis of population served, the summary statistic generated an approximate 10% difference in the population exposed to arsenic concentrations > 10 μg/L. The research described in this article furthers the discussion of what information is needed to accurately predict nationwide arsenic occurrence, exposure, and health outcomes.
  • AGU 2013 Fall Meeting AbstractsU. Lall, N. Devineni, T. Troy, B. Rahill-Marier, A.W. Robertson, P. Gentine, A.M. Greene, E.R. Cook, T.A. Russo, M. Lu, K.L. Tully, J.E. Hickman, C. Palm, F. D’Andrea, A.K. Betts, M.F. Guerin, C. Karamperidou, M. A. Cane, D. Farnham, N. Rochetin, P. Gen, 2013-12-09
  • Neural Network–Based Sensitivity Analysis of Summertime Convection over the Continental United StatesFilipe Aires, Pierre Gentine, Kirsten L. Findell, Benjamin R. Lintner, and Christopher Kerr, 2013-11-09 [+]
    ABSTRACT: Although land–atmosphere coupling is thought to play a role in shaping the mean climate and its variability, it remains difficult to quantify precisely. The present study aims to isolate relationships between early morning surface turbulent fluxes partitioning [i.e., evaporative fraction (EF)] and subsequent afternoon convective precipitation frequency and intensity. A general approach involving statistical relationships among input and output variables, known as sensitivity analysis (SA), is used to develop a reduced complexity metamodel of the linkage between EF and convective precipitation. Two additional quantities characterizing the early morning convective environment, convective triggering potential (CTP) and low-level humidity (HIlow) deficit, are included. The SA approach is applied to the North American Regional Reanalysis (NARR) for June–August (JJA) conditions over the entire continental United States, Mexico, and Central America domain. Five land–atmosphere coupling regimes are objectively characterized based on CTP, HIlow, and EF. Two western regimes are largely atmospherically controlled, with a positive link to CTP and a negative link to HIlow. The other three regimes occupy Mexico and the eastern half of the domain and show positive links to EF and negative links to HIlow, suggesting that both surface fluxes and atmospheric humidity play a role in the triggering of rainfall in these regions. The regimes associated with high mean EF also tend to have high sensitivity of rainfall frequency to variations in EF. While these results may be sensitive to the choice of dataset, the approach can be applied across observational, reanalysis, and model datasets and thus represents a potentially powerful tool for intercomparison and validation as well as for characterizing land–atmosphere interaction regimes.
  • Optimal Crop Choice, Irrigation Allocation, and the Impact of Contract FarmingWT Huh, U Lall, 2013-09
  • Evaluation of a simple approach for crop evapotranspiration partitioning and analysis of the water budget distribution for several crop speciesPierre Béziat, Vincent Rivalland, Tiphaine Tallec, Nathalie Jarosz, Gilles Boulet,Pierre Gentine, and Eric Ceschia, 2013-08-15 [+]
    Abstract: Climate variability and climate change induce important intra- and inter-annual variability of precipitation that significantly alters the hydrologic cycle. The surface water budgets and the plant or ecosystem water use efficiency (WUE) are in turn modified. Obtaining greater insight into how climatic variability and agricultural practices affect water budgets and regarding their components in croplands is, thus, important for adapting crop management and limiting water losses. Therefore, the principal objectives of this study are: (1) to assess the contribution of different components to the agro-ecosystem water budget and (2) to evaluate how agricultural practices and climate modify the components of the surface water budget. To achieve these goals, we tested a new method for partitioning evapotranspiration (ETR), measured by means of an eddy-covariance method, into soil evaporation (E) and plant transpiration (TR) based on marginal distribution sampling (MDS). The partitioning method proposed requires continuous flux recording and measurements of soil temperature and humidity close to the surface, global radiation above the canopy and assessment of leaf area index dynamics. This method is well suited for crops because it requires a dataset including long bare-soil periods alternating with vegetated periods for accurate partitioning estimation. We compared these estimations with calibrated simulations of the ICARE-SVAT double source mechanistic model. The results showed good agreement between the two partitioning methods, demonstrating that MDS is a convenient, simple and robust tool for estimating E with reasonable associated uncertainties. During the growing season, the proportion of E in ETR was approximately one-third and varied mainly with crop leaf area. When calculated on an annual time scale, the proportion of E in ETR reached more than 50%, depending on the crop leaf area and on the duration and distribution of bare soil within the year.
  • Emergent relation between surface vapor conductance and relative humidity profiles yields evaporation rates from weather dataGD Salvucci and P Gentine, Online Early Edition of Proceedings of the National Academy of Sciences, 2013-04-01 [+]
    Abstract: The ability to predict terrestrial evapotranspiration (E) is limited by the complexity of rate-limiting pathways as water moves through the soil, vegetation (roots, xylem, stomata), canopy air space, and the atmospheric boundary layer. The impossibility of specifying the numerous parameters required to model this process in full spatial detail has necessitated spatially upscaled models that depend on effective parameters such as the surface vapor conductance (Csurf). Csurf accounts for the biophysical and hydrological effects on diffusion through the soil and vegetation substrate. This approach, however, requires either site-specific calibration of Csurf to measured E, or further parameterization based on metrics such as leaf area, senescence state, stomatal conductance, soil texture, soil moisture, and water table depth. Here, we show that this key, rate-limiting, parameter can be estimated from an emergent relationship between the diurnal cycle of the relative humidity profile and E. The relation is that the vertical variance of the relative humidity profile is less than would occur for increased or decreased evaporation rates, suggesting that land–atmosphere feedback processes minimize this variance. It is found to hold over a wide range of climate conditions (arid–humid) and limiting factors (soil moisture, leaf area, energy). With this relation, estimates of E and Csurf can be obtained globally from widely available meteorological measurements, many of which have been archived since the early 1900s. In conjunction with precipitation and stream flow, long-term E estimates provide insights and empirical constraints on projected accelerations of the hydrologic cycle.
  • A Probabilistic Bulk Model of Coupled Mixed Layer and Convection. Part II: Shallow Convection CasePierre Gentine, Alan K. Betts, Benjamin R. Lintner, Kirsten L. Findell, Chiel C. Vanheerwaarden, Alexandra Tzella, And Fabio D’andrea , 2013-01-14 [+]
    ABSTRACT: The probabilistic bulk convection model (PBCM) developed in a companion paper is here extended to shallow nonprecipitating convection. The PBCM unifies the clear-sky and shallow convection boundary layer regimes by obtaining mixed-layer growth, cloud fraction, and convective inhibition from a single parameterization based on physical principles. The evolution of the shallow convection PBCM is based on the statistical distribution of the surface thermodynamic state of convective plumes. The entrainment velocity of the mixed layer is related to the mass flux of the updrafts overshooting the dry inversion capping the mixed layer. The updrafts overcoming the convective inhibition generate active cloudbase mass flux, which is the boundary condition for the shallow cumulus scheme. The subcloud-layer entrainment velocity is directly coupled to the cloud-base mass flux through the distribution of vertical velocity and fractional cover of the updrafts. Comparisons of the PBCM against large-eddy simulations from the Barbados Oceanographic and Meteorological Experiment (BOMEX) and from the Southern Great Plains Atmospheric Radiation Measurement Program (ARM) facility demonstrate good agreement in terms of thermodynamic structure, cloud-base mass flux, and cloud top. The equilibrium between the cloud-base mass flux and rate of growth of the mixed layer determines the equilibrium convective inhibition and cloud cover. This process is an important new insight on the coupling between the mixed-layer and cumulus dynamics. Given its relative simplicity and transparency, the PBCM represents a powerful tool for developing process-based understanding and intuition about the physical processes involved in boundary layer–convection interactions, as well as a test bed for diagnosing and validating shallow convection parameterizations.
  • A Probabilistic Bulk Model of Coupled Mixed Layer and Convection. Part I: Clear-Sky CasePierre Gentine, Alan K. Betts, Benjamin R. Lintner, Kirsten L. Findell, Chiel C. Vanheerwaarden, Alexandra Tzella, And Fabio D’andrea , 2013-01-11 [+]
    ABSTRACT: A new bulk model of the convective boundary layer, the probabilistic bulk convection model (PBCM), is presented. Unlike prior bulk approaches that have modeled the mixed-layer-top buoyancy flux as a constant fraction of the surface buoyancy flux, PBCM implements a new mixed-layer-top entrainment closure based on the mass flux of updrafts overshooting the inversion. This mass flux is related to the variability of the surface state (potential temperature u and specific humidity q ) of an ensemble of updraft plumes. The authors evaluate the model against observed clear-sky weak and strong inversion cases and show that PBCM performs well. The height, state, and timing of the boundary layer growth are accurately reproduced. Sensitivity studies are performed highlighting the role of the main parameters (surface variances, lateral entrainment). The model is weakly sensitive to the exact specification of the variability at the surface and is most sensitive to the lateral entrainment of environmental air into the rising plumes. Apart from allowing time-dependent top-of- the-boundary-layer entrainment rates expressed in terms of surface properties, which can be observed in situ, PBCM naturally takes into account the transition to the shallow convection regime, as described in a companion paper. Thus, PBCM represents an important step toward a unified framework bridging parameterizations of mixed-layer entrainment velocity in both clear-sky and moist convective boundary layers.
  • Precipitation Sensitivity to Surface Heat Fluxes over North America in Reanalysis and Model DataAlexis Berg, Kirsten Findell, Benjamin R. Lintner, Pierre Gentine, and Christopher Kerr, 2013 [+]
    ABSTRACT: A new methodology for assessing the impact of surface heat fluxes on precipitation is applied to data from the North American Regional Reanalysis (NARR) and to output from the Geophysical Fluid Dynamics Laboratory’s Atmospheric Model 2.1 (AM2.1). The method assesses the sensitivity of afternoon convective rainfall frequency and intensity to the late-morning partitioning of latent and sensible heating, quantified in terms of evaporative fraction (EF). Over North America, both NARR and AM2.1 indicate sensitivity of convective rainfall triggering to EF but no appreciable influence of EF on convective rainfall amounts. Functional relationships between the triggering feedback strength (TFS) metric and mean EF demonstrate the occurrence of stronger coupling for mean EF in the range of 0.6 to 0.8. To leading order, AM2.1 exhibits spatial distributions and seasonality of the EF impact on triggering resembling those seen in NARR: rainfall probability increases with higher EF over the eastern United States and Mexico and peaks in Northern Hemisphere summer. Over those regions, the impact of EF variability on afternoon rainfall triggering in summer can explain up to 50% of seasonal rainfall variability. However, the AM2.1 metrics also exhibit some features not present in NARR, for example, strong coupling extending northwestward from the central Great Plains into Canada. Sources of disagreement may include model hydroclimatic biases that affect the mean patterns and variability of surface flux partitioning, with EF variability typically much lower in NARR. Finally, the authors also discuss the consistency of their results with other assessments of land–precipitation coupling obtained from different methodologies.
  • Diagnosing evaporative fraction over land from boundary-layer cloudsPierre Gentine, Craig R. Ferguson, and Albert A.M. Holtslag, 2013 [+]
    Abstract: The potential use of continental fair -weather shallow cumuli as a way to retrieve the daily surface evaporative fraction over land is evaluated in convective conditions. The proposed method utilizes the fact that both the timing of cloud occurrence and the cloud base height at the time of occurrence provide strong constraints on the surface energy balance and evaporative fraction. The retrieval is especially reliable in the presence of relatively stable and humid free troposphere profiles. The advantage of the method is that it provides a more direct estimate of the surface evaporative fraction than indirect estimation based on inversion of a highly parameterized land surface model. In addition, the evaporative fraction is obtained at a scale of a few kilometers, which is more pertinent for weather and climate studies. The retrieval strategy is tested and validated for three contrasting climates: the U.S. southern Great Plains, West Africa, and the Netherlands. We suggest that the use of satellite observations of shallow cumuli can help constrain the retrieval of the surface evaporative fraction within a data assimilation scheme/reanalysis.
  • A Worldwide Comparison of Water Use Efficiency of Crop ProductionZ Wu, U Lall, M Zhao | Applied Mechanics and Materials, 2013
  • Reduction 
of tropical land region precipitation variability via transpirationLee, J. E., Lintner, B. R., Neelin, J. D., Jiang, X., Gentine, P., Boyce, C. K., et al., 2012-10-03 [+]
    Tropical rainforests are known to exhibit low intraseasonal precipitation variability compared with oceanic areas with similar mean precipitation in observations and models. In the present study, the potential role of transpiration for this difference in precipitation variability is investigated using the National Center for Atmospheric Research (NCAR) atmospheric general circulation model. Comparing model results with and without transpiration shows that in the absence of transpiration, mean precipitation decreases as may be expected. However the incidence of both higher daily total column water and more intense precipitation increases without transpiration; consequently the variability of precipitation increases substantially. These results can be understood in terms of the complex interplay of local near- surface and remote moist dynamical processes with both local positive (boundary-layer drying) and large-scale negative (increased large-scale convergence) feedbacks when transpiration is disabled in the model. It is also shown that surface turbulent fluxes over tropical rainforests are highly correlated with incoming solar energy but only weakly correlated with wind speed, possibly decoupling land precipitation from large-scale disturbances like the Madden-Julian Oscillation.
  • Towards Greater Accountability and Efficiency in Groundwater and Energy Use in Indian Agriculture Initial Report from a Field Pilot in Gujarat, IndiaRam Fishman, Vijay Modi, Kapil Narula, Sahil Gulati, Sandeep Mahajan, Nikunj Parekh, Dishant Patel, Ankur Patel, Anil Kumar Rohila, Upmanu Lall, 2012-09-28 [+]
    A novel policy mechanism to introduce metering and incentivize water and energy use efficiency was recently co-piloted by the Columbia Water Center (CWC), the Government of Gujarat, and the Northern Gujarat Utility Company (UGVCL). Recognizing the political difficulty of charging farmers the full cost of electricity, the mechanism indirectly introduces a marginal cost, by transferring to farmers financial savings (in generation costs) that result from voluntary reductions in usage.
  • Designing Sustainable and Scalable Rural Water Supply Systems: Evidence and Lessons from Northeast BrazilTanya Heikkila, Francisco Osny Enéas da Silva, Daniel Stellar, Francisco de Assis de Souza Filho, Samantha Tress, Upmanu Lall, 2012-08-21 [+]
    The Columbia Water Center initiated a project in northeast Brazil, in the state of Ceará, where many rural communities lack access to safe, reliable drinking water. Obstacles to implementing safe drinking water supply systems are common in many developing country settings, which highlight the need for a systematic approach to sustainable design and operation of a scalable, rural water supply system based on an analysis of the local physical, environmental and socioeconomic contexts.
  • Systematic errors in ground heat flux estimation and their correctionP. Gentine, D. Entekhabi, and B. Heusinkveld, 2012-08-08 [+]
    Incoming radiation forcing at the land surface is partitioned among the components of the surface energy balance in varying proportions depending on the time scale of the forcing. Based on a land-atmosphere analytic continuum model, a numerical land surface model, and field observations we show that high-frequency fluctuations in incoming radiation (with period less than 6 h, for example, due to intermittent clouds) are preferentially partitioned toward ground heat flux. These higher frequencies are concentrated in the 0–1 cm surface soil layer. Subsequently, measurements even at a few centimeters deep in the soil profile miss part of the surface soil heat flux signal. The attenuation of the high-frequency soil heat flux spectrum throughout the soil profile leads to systematic errors in both measurements and modeling, which require a very fine sampling near the soil surface (0–1 cm). Calorimetric measurement techniques introduce a systematic error in the form of an artificial band-pass filter if the temperature probes are not placed at appropriate depths. In addition, the temporal calculation of the change in the heat storage term of the calorimetric method can further distort the reconstruction of the surface soil heat flux signal. A correction methodology is introduced which provides practical application as well as insights into the estimation of surface soil heat flux and the closure of surface energy balance based on field measurements.
  • Restoring Groundwater in Punjab, India's Breadbasket: Finding Agricultural Solutions for Water SustainabilityShama Perveen, Chandra Kiran Krishnamurthy, Rajinder S. Sidhu, Kamal Vatta, Baljinder Kaur, Vijay Modi, Ram Fishman, Lakis Polycarpou, Upmanu Lall, 2012-06-26 [+]
    This white paper presents the initial results of an investigation into the question of weather water use in rice-wheat cropping systems can be brought into balance in Punjab, India. In the first phase, the research attempted to identify one or more technologies or practices that are purported to save water in rice cultivation, and were attractive to farmers for adoption through a structured field test. In the second phase, the project team has developed and is pursuing a strategy to rapidly recruit farmers to scale up the application of the tensiometer, the most successful of the approaches tested in the first phase.
  • An idealized prototype for large-scale land-atmosphere couplingBenjamin R. Lintner, Pierre Gentine, Kirsten L. Findell, Fabio D’andrea,Adam H. Sobel, and Guido D. Salvucci, 2012-04-01 [+]
    ABSTRACT: A process-based, semianalytic prototype model for understanding large-scale land–atmosphere coupling is developed here. The metric for quantifying the coupling is the sensitivity of precipitation P to soil moisture W, DP/DW. For a range of prototype parameters typical of conditions found over tropical or summertime continents, the sensitivity measure exhibits a broad minimum at intermediate soil moisture values. This minimum is attributed to a trade-off between evaporation (or evapotranspiration) E and large-scale moisture convergence across the range of soil moisture states. For water-limited, low soil moisture conditions, DP/DW is dominated by evaporative sensitivity DE/DW, reflecting high potential evaporation E p arising from rela- tively warm surface conditions and a moisture-deficient atmospheric column under dry surface conditions. By contrast, under high soil moisture (or energy limited) conditions, DE/D W becomes slightly negative as E p decreases. However, because convergence and precipitation increase strongly with decreasing (drying) moisture advection, while soil moisture slowly saturates, DP/DW is large. Variation of key parameters is shown to impact the magnitude of DP/DW, for example, increasing the time scale for deep convective adjustment lowers DP/DW at a given W, especially on the moist side of the profile where convergence dominates. While the prototype’s applicability for direct quantitative comparison with either observations or models is clearly limited, it nonetheless demonstrates how the complex interplay of surface turbulent and column radiative fluxes, deep convection, and horizontal and vertical moisture transport influences the coupling of the land surface and atmosphere that may be expected to occur in either more realistic models or observations.
  • Scaling in Surface Hydrology: Progress and ChallengesPierre Gentine, Tara J. Troy, Benjamin R. Lintner, and Kirsten L. Findell, 2012-03 [+]
    Abstract: This paper presents a review of the challenges in spatial and temporal scales in surface hydrology. Fundamental issues and gaps in our understanding of hydrologic scaling are highlighted and shown to limit predictive skill, with heterogeneities, nonlinearities, and non-local transport processes among the most significant difficulties faced in scaling. The discrepancy between the physical process scale and the measurement scale has played a major role in restricting the development of theories, for example, relating observational scales to scales of climate and weather models. Progress in our knowledge of scaling in hydrology requires systematic determination of critical scales and scale invariance of physical processes. In addition, viewing the surface hydrologic system as composed of interacting dynamical subsystems should facilitate the definition of scales observed in nature. Such an approach would inform the development of careful, resolution-dependent, physical law formulation based on mathematical techniques and physical laws.
  • India's Deepening Water Crisis? Water Risks for Indian Industries: A Preliminary Study of 27 Industrial SectorsShama Perveen, Romit Sen, Mayuri Ghosh, 2012-02-01 [+]
    The Columbia Water Center and the Federation of Indian Chambers of Commerce and Industry undertook a preliminary national level geospatial study of water risks perceptions and responses across 27 industrial sectors in India, including food processing, textiles, energy, oil and gas, retail, pharmaceuticals, information technology and health services.
  • Interdependence of climate, soil, and vegetation as constrained by the Budyko curvePierre Gentine, Paolo D’Odorico, Benjamin R. Lintner, Gajan Sivandran, and Guido Salvucci, 2012 [+]
    The Budyko curve is an empirical relation among evapotranspiration, potential evapotranspiration and precipitation observed across a variety of landscapes and biomes around the world. Using data from more than three hundred catchments and a simple water balance model, the Budyko curve is inverted to explore the ecohydrological controls of the soil water balance. Comparing the results across catchments reveals that aboveground transpiration efficiency and belowground rooting structure have adapted to the dryness index and the phase lag between peak seasonal radiation and precipitation. The vertical and/or lateral extent of the rooting zone exhibits a maximum in semi-arid catchments or when peak radiation and precipitation are out of phase. This demonstrates plant strategies in Mediterranean climates in order to cope with water stress: the deeper rooting structure buffers the phase difference between precipitation and radiation. Results from this study can be used to constrain land-surface parameterizations in ungauged basins or general circulation models.
  • Contract farming with possible reneging in a developing country: Can it work?WT Huh, S Athanassoglou, U Lall | IIMB Management Review, 2012 [+]
    We consider a processed-food manufacturer that faces uncertain exogenous demand and procures a farm crop either from the outside market or from local farmers via contract farming. The contract price is determined at the beginning of the season when the market price is still uncertain. When the market price is realised, we allow the farmer the possibility of reneging from the contract, which occurs if the market price is sufficiently high. We show that granting farmers the option of reneging on the contract may improve the manufacturer’s expected profit, and identify the conditions under which such an improvement can be expected.
  • Is an Epic Pluvial Masking the Water Insecurity of the Greater New York City Region?Neil Pederson, Andrew R. Bell, Edward R. Cook, Upmanu Lall, Naresh Devineni, Richard Seager, Keith Eggleston, Kevin J. Vranes, 2012 [+]
    ABSTRACT: Six water emergencies have occurred since 1981 for the New York City region (NYC) despite: 1) its perhumid climate, 2) substantial conservation of water since 1979 and 3) meteorological data showing little severe or extreme drought since 1970. We reconstruct 472 years of moisture availability for the NYC watershed to place these emergencies in long-term hydroclimatic context. Using nested reconstruction techniques, 32 tree-ring chronologies comprised of 12 species account for up to 66.2% of the average May-August Palmer Drought Severity Index. Verification statistics indicate good statistical skill from 1531-2003. The use of multiple tree species, including rarely-used species that can sometimes occur on mesic sites like Liriodendron tulipifera, Betula lenta and Carya spp., seems to aid reconstruction skill. Importantly, the reconstruction captures pluvial events in the instrumental record nearly as well as drought events and is significantly correlated to precipitation over much of the northeastern US. While the mid-1960s drought is a severe drought in the context of the new reconstruction, the region experienced repeated droughts of similar intensity, but greater duration during the 16th and 17th centuries. The full record reveals a trend towards more pluvial conditions since ca 1800 that is accentuated by an unprecedented, 43-year pluvial event that continues through 2011. In the context of the current pluvial, decreasing water usage, but increasing extra-urban pressures, it appears that the water supply system for the greater NYC region could be severely stressed if the current water boom shifts towards hydroclimatic regimes like the 16th and 17th centuries.
  • Developing Sustainable and Replicable Water Supply Systems in Rural Communities in BrazilFrancisco Osny Enéas da Silva, Tanya Heikkila, Francisco de Assis de Souza Filho, Daniele Costa da Silva. The International Journal of Water Resources Development, 2012 [+]
    Abstract: This article examines the challenges and opportunities for developing rural water supply programs that can meet multiple sustainability criteria, including social, technical/administrative and environmental criteria, and can be replicated beyond individual communities. It draws lessons from a water supply development project in Northeast Brazil, identifying how environmental and community assessments, community engagement in planning, as well as training, capacity building, and monitoring can help meet sustainability criteria. The article further explores how an institutionalized planning process and partnerships with public agencies and donors are integrated into the project design to support replicability.
  • The Role of Cross-Scale Inst Linkages in Common Pool Resource Management: Assessing Interstate RiverTanya Heikkila, Edella Schlager and Mark W. Davis | Policy Studies Journal, 2011 [+]
    Abstract: This article extends the Institutional Analysis and Development Framework’s seminal research on common pool resource (CPR) management in new directions by exploring how the design principles of robust and enduring CPR management, initially proposed by Elinor Ostrom in 1990, can be used to measure and assess cross-scale institutional linkages. This study examines data from 14 interstate river basin compacts in the western United States to identify the types of linkages established in these interstate settings, the factors that contribute to the emergence of diverse types of linkages around these shared resources, and how different types of linkages perform. Using Ostrom’s CPR design principles to operationalize and measure linkages, the study shows that diverse types of cross-scale linkages were created under the 14 interstate compacts, with linkages related to monitoring found to be particularly prevalent. The types and diversity of linkages can largely be explained by the conditions under which compacts emerged and the water management issues states jointly face. In applying the evaluative criteria operationalized by the CPR design principles, this research further shows that the monitoring and collective choice linkages created by compacts tend to be of higher quality, while enforcement and conflict resolution linkages appeared to be of the lowest quality. In addition to developing the IAD literature on CPR management, these findings offer critical insights for assessing the capacity of interstate river basin compacts in the western United States to manage shared resources successfully, as well as insights for what types of institutional investments may be needed for enhanced resource governance.
  • Fecal Contamination of Shallow Tubewells in Bangladesh Inversely Related to ArsenicAlexander van Geen, Kazi Matin Ahmed, Yasuyuki Akita, Md. Jahangir Alam, Patricia Culligan, Brian Ma | Environmental Science & Technology, 2011 [+]
    Abstract: : The health risks of As exposure due to the installation of millions of shallow tubewells in the Bengal Basin are known, but fecal contamination of shallow aquifers has not systematically been examined. This could be a source of concern in densely populated areas with poor sanitation because the hydraulic travel time from surface water bodies to shallow wells that are low in As was previously shown to be considerably shorter than for shallow wells that are high in As. In this study, 125 tubewells 6-36 m deep were sampled in duplicate for 18 months to quantify the presence of the fecal indicator Escherichia coli. On any given month, E. coli was detected at levels exceeding 1 most probable number per 100 mL in 19-64% of all shallow tubewells, with a higher proportion typically following periods of heavy rainfall. The frequency of E. coli detection averaged over a year was found to increase with population surrounding a well and decrease with the As content of a well, most likely because of downward transport of E. coli associated with local recharge. The health implications of higher fecal contamination of shallow tubewells, to which millions of households in Bangladesh have switched in order to reduce their exposure to As, need to be evaluated.
  • CWC White Paper: Addressing the Water Crisis in Gujarat, IndiaVijay Modi, Kapil Narula, Ram Fishman, Lakis Polycarpou | White Paper pdf, 2011 [+]
    Abstract: This paper presents the results of the Columbia Water Center’s study of the severe groundwater crisis in the Mehsana region of Northern Gujarat, India. The study concludes that the current pattern of groundwater exploitation is both costly for the state and unsustainable for farmers, and could lead to the complete failure of agriculture in the area within a few years if left unchecked. The study, funded by the PepsiCo Foundation, was conducted as the first phase of a CWC project to design more sustainable policy options to help conserve water and energy while improving farmer incomes in North Gujarat; future papers will outline the initial outcomes of the area pilot project along with resulting recommendations for policymakers in the area.
  • Building a Theory of Learning in Collaboratives: Evidence from the Everglades Restoration ProgramAndrea K. Gerlak, Tanya Heikkila | Journal of Public Administration Research and Theory Advance Access, 2011 [+]
    Abstract: Many of society’s most vexing problems must be solved through collaborative arrangements. Growing scholarly interest in collaboratives recognizes that the capacity for collective learning may play a critical role in their success. However, limited theoretical or empirical research exists to explain how learning occurs and the conditions that support learning in this context. In this article, we draw upon a wealth of literature, ranging from organization theory, policy process and change, and network analysis, to establish a framework of collective learning to guide inquiry in learning in collaborative governance settings. We apply our learning framework to a study of learning in a collaborative ecosystem restoration program in the Florida Everglades. We use the framework to guide a study of how learning processes and products are linked within a collaborative using a case-based, inductive approach at two levels of analysis—the larger program level and the subcase level of a learning product case. Our multilevel analysis draws upon survey and interview data to examine how the framework helps diagnose the specific types of learning processes and products that emerge in this setting, as well as the factors that influence these learning processes. In doing so, the analysis illuminates theoretical propositions, not explained by the broader literature on collective learning, around the structural, social, and technological features of the collaborative, which may foster learning.
  • Emissions Credits: Opportunity To Promote Integrated Nitrogen Management in the Wastewater SectorJames S. Wang, Steven P. Hamburg, Donald E. Pryor, Kartik Chandran, and Glen T. Daigger | Environmental Science & Technology, 2011 [+]
    Abstract: Relatively little attention has been paid to integrating gaseous N2O generated by wastewater treatment into overall reactive nitrogen (Nr) pollution reduction. We propose that there is potential for substantial reductions in N2O emissions through the addition of denitrification processes to existing nitrifying wastewater treatment plants (WWTPs), which are designed to lower ammonia levels but currently do not reduce overall Nr. In addition to providing the bene?t of reducing total nitrogen concentrations in the effluent, this kind of WWTP upgrade has been demonstrated to reduce energy consumption and fossil CO2 emissions. We show that the creation of a greenhouse gas (GHG) crediting system for the wastewater sector could provide a potentially sizable economic incentive on the order of $10 million to $600 million per year in the U.S. for upgrading of nitrifying WWTPs that results in N2O reductions, with an ancillary benefit of another $30100 million per year from electricity savings. Even if biological nitrogen removal (BNR) treatment were mandated by existing and future water quality regulations, a GHG crediting system could still be created to promote BNR design and operation that drive N2O emissions below a baseline to even lower levels. In this case GHG credits could offset around 0.570% of the operating and maintenance cost for the BNR.
  • Analyzing Feasibility of Pricing in Sustainable Irrigation Water Governance Reform in Punjab, IndiaTatsuhiko Sato | Swedish University of Agricultural Sciences, 2011 [+]
    Abstract: India faces water management challenges. The agriculture sector is the largest user and polluter of water but the water resource management has had a duality of good design and poor implementation. The agricultural water management is in a conflict between institutional and political priorities in ensuring security for food and rural livelihood. In Punjab, a concern is growing about sustainability among farming community over income and production of rice and of freshwater for needs of farmers and increasingly for non-agricultural sectors. The political pressure for efficiency of water use and for conservation and allocation is growing but necessitates a critical analysis as to whether this constitutes the most effective and only prescription to overcome the challenge Punjab faces. There is an ambiguity in the concept of economic efficiency especially of defining cost and value of water and conditions surrounding production and livelihood of individual farmer in the state complicate rather than simplify the question of appropriateness and validity of application of optimal water and/or electricity pricing in Punjab. Various findings and discussions show how this may be the case and indicate very broad issues such as international trade that requires coordination among wide ranging departments and stakeholders to identify suitable mix of options available for Punjab.
  • Optimal Mechanisms for Heterogeneous Multi-cell AquifersStergios Athanassoglou, Tobias Siegfried, Glenn Sheriff, Woonghee Tim Huh | Fondazione Eni Enrico Mattei Working Papers, 2011 [+]
    Abstract: Standard economic models of groundwater management impose restrictive assumptions regarding perfect transmissivity (i.e., the aquifer behaves as a bath- tub), no external e ects of groundwater stocks, observability of individual ex- traction rates, and/or homogenous agents. In this article, we derive regulatory mechanisms for inducing the socially optimal extraction path in Markov perfect equilibrium for aquifers in which these assumptions do not hold. In spite of the complexity of the underlying system, we identify an interesting case in which a simple linear mechanism achieves the social optimum. To illustrate potential problems that can arise by erroneously imposing simplifying assumptions, we conduct a simulation based on data from the Indian state of Andhra Pradesh.
  • Water Use of Oilseed CropsRob Aiken, Freddie Lamm, Abdrabbo A Shehata Aboukheira | 23rd Annual Central Plains Irrigation Conference, 2011 [+]
    Abstract: Water use of a crop, with adequate available soil water supply, is primarily affected by its canopy and weather conditions (Tanner and Sinclair, 1983; Albrizio and Steduto. 2005; Suyker and Verma, 2010). These effects are represented by seasonal crop coefficients and the potential evaporative demand (ETp) of the atmosphere (Allen et al., 2005). The crop coefficient indicates the fraction of potential ET which the crop is expected to utilize on a given day. The crop coefficient value typically changes with crop stage. Crop water productivity (also known as water use efficiency) refers to the amount of biomass or economic yield produced with a given amount of water use. This article will present oilseed crop water use and crop water productivity field results from the U.S. central High Plains. Also, we review findings of environmental and management factors which can improve the water productivity of oilseed crops in this region.
  • Water Quality Violations and Avoidance Behavior: Evidence from Bottled Water ConsumptionJoshua Graff Zivin, Matthew Neidell, Wolfram Schlenker | National Bureau of Economic Research Working Paper, 2011 [+]
    Abstract: In this paper, we examine the impact of poor water quality on avoidance behavior by estimating the change in bottled water purchases in response to drinking water violations. Using data from a national grocery chain matched with water quality violations, we find an increase in bottled water sales of 22 percent from violations due to microorganisms and 17 percent from violations due to elements and chemicals. Back-of-the envelope calculations yield costs of avoidance behavior at roughly $60 million for all nationwide violations in 2005, which...
  • Insights from a joint analysis of Indian and Chinese monsoon rainfall dataM. Zhou, F. Tian, U. Lall, and H. Hu | Journal of Hydrology and Earth System Sciences, 2011 [+]
    Abstract: Monsoon rainfall is of great importance for the agricultural production in both China and India. Understanding its rule and possibility of long term prediction is a challenge for research. This paper gives a joint analysis of Indian monsoon and Chinese monsoon, 5 ?nds their teleconnection to Sea Surface Temperature anomaly (SSTa) and other climate indices individually and relationship in common. The results show that northern China garners less rainfall when whole Indian rainfall is below normal. Also, with cold SSTa over the Indonesia region, more rainfall would be distributed over India and South China.
  • Over-Extraction from Shallow Bedrock versus Deep Alluvial Aquifers: Reliability versus SustainabilityRam Fishman, Tobias Siegfried, Pradeep Raj, Vijay Modi, and Upmanu Lall | Accepted by Water Resources Research, 2011 [+]
    Abstract: The excessive exploitation of aquifers is emerging as a world- wide problem, but it is nowhere as dramatic and consequential as it is in In- dia, the world's largest groundwater consumer for irrigation. While the prob- lem is usually framed in terms of long-term depletion of fossil aquifers, we focus here on the agricultural implications of over-exploitation in aquifer of limited storage, such as those that underlie most of peninsular India, by con- trasting water table and irrigation dynamics in two irrigation intensive re- gions of India that di er in underlying hydrogeology. In the deep alluvial aquifers of Punjab of north-western India, water table dynamics are dominated by declining trends, while in the hard rock, shallow aquifer region of Telangana in southern-central India, dynamics are dominated by short-term fluctua- tions. We show that irrigation from the deep aquifers in Punjab is largely unaff ected by fluctuations in water tables and rainfall, but in the hard rock shallow aquifers of Telangana, irrigation is more variable and sensitive to these stochastic variables. These ndings indicate that energy and land are the bind- ing constraints to irrigation in Punjab, but physical water scarcity is the bind- ing constraint in Telangana. We argue that over-exploitation of a deep aquifer is primarily an issue of long-term sustainability, whereas in a shallow aquifer, it leads to increased short-term variability in irrigation and a loss of bu er- ing capacity which can be harmful economically.
  • Will climate change exacerbate water stress in Central Asia?T Siegfried, T Bernauer, R Guiennet, S Sellars, A W. Robertson, J Mankin, P Bauer-Gottwein, A Yakov | Climate Change, 2011 [+]
    Abstract: Millions of people in the geopolitically important region of Central Asia depend on water from snow- and glacier-melt driven international rivers, most of all the Syr Darya and Amu Darya. The riparian countries of these rivers have experienced recurring water allocation conflicts ever since the Soviet Union collapsed. Will climate change exacerbate water stress and thus conflicts? We have developed a coupled climate, land-ice and rainfall-runoff model for the Syr Darya to quantify impacts and show that climatic changes are likely to have consequences on runoff seasonality due to earlier snow-melt. This will increase water stress in unregulated catchments because less water will be available for irrigation in the summer months. Threats from geohazards, above all glacier lake outbursts, are likely to increase as well. The area at highest risk is the densely populated, agriculturally productive, and politically unstable Fergana Valley. Targeted infrastructural developments will be required in the region. If the current mismanagement of water and energy resources can be replaced with more effective resource allocation mechanisms through the strengthening of transboundary institutions, Central Asia will be able to successfully address these future climate-related challenges.
  • Protocol for the Measurement of Nitrous Oxide Fluxes from Biological Wastewater Treatment PlantsKartik Chandran | Methods in Enzymology, 2011 [+]
    Abstract: The overarching goal herein was to develop a protocol that could be used to generate consistent information on the generation and emission of nitrous oxide (N2O) from open-surface wastewater treatment bioreactors. The developed protocol was reviewed and endorsed by the United States Environmental Protection Agency (USEPA), whereupon it was used to determine N2O emissions from a wide array of wastewater treatment processes across the United States. Scaled-down variants of the protocol have also since been adopted for lab-scale measurements. The protocol consists of a combination of elements that entail real-time online measurement of headspace N2O concentrations, supplemented by discrete measurements of liquid-phase N2O and other routinely monitored wastewater and process parameters. Notably, the advective flow rate of headspace gas is also directly measured.
  • Probability of afternoon precipitation in eastern United States and Mexico enhanced by high...Kirsten L. Findell, Pierre Gentine, Benjamin R. Lintner and Christopher Kerr | Nature Geoscience, 2011 [+]
    Moisture and heat fluxes from the land surface to the atmosphere form a critical nexus between surface hydrology and atmospheric processes, particularly those relevant to precipitation. Although current theory suggests that soil moisture generally has a positive impact on subsequent precipitation, individual studies have shown support both for 1–4 and against 5–7 this positive feedback. Broad assessment of the coupling between soil moisture and evapotranspiration, and evapotranspiration and precipitation, has been limited by a lack of large-scale observations. Quantification of the influence of evapotranspiration on precipitation remains particularly uncertain. Here, we develop and apply physically based, objective metrics for quantifying the impacts of surface evaporative and sensible heat fluxes on the frequency and intensity of convective rainfall during summer, using North American reanalysis data. We show that high evaporation enhances the probability of afternoon rainfall east of the Mississippi and in Mexico. Indeed, variations in surface ?uxes lead to changes in afternoon rainfall probability of between 10 and 25% in these regions. The intensity of rainfall, by contrast, is largely insensitive to surface ?uxes. We suggest that local surface fluxes represent an important trigger for convective rainfall in the eastern United States and Mexico during the summer, leading to a positive evaporation– precipitation feedback.
  • Predicting foraging wading bird populations in Everglades National Park from seasonal hydrologic...Hyun-Han Kwon, Upmanu Lall, Vic Engel | Water Resources Research, 2011 [+]
    Abstract: The ability to map relationships between ecological outcomes and hydrologic conditions in the Everglades National Park (ENP) is a key building block for their restoration program, a primary goal of which is to improve conditions for wading birds. This paper presents a model linking wading bird foraging numbers to hydrologic conditions in the ENP. Seasonal hydrologic statistics derived from a single water level recorder are well correlated with water depths throughout most areas of the ENP, and are effective as predictors of wading bird numbers when using a nonlinear hierarchical Bayesian model to estimate the conditional distribution of bird populations. Model parameters are estimated using a Markov chain Monte Carlo (MCMC) procedure. Parameter and model uncertainty is assessed as a byproduct of the estimation process. Water depths at the beginning of the nesting season, the average dry season water level, and the numbers of reversals from the dry season recession are identified as significant predictors, consistent with the hydrologic conditions considered important in the production and concentration of prey organisms in this system. Long-term hydrologic records at the index location allow for a retrospective analysis (1952–2006) of foraging bird numbers showing low frequency oscillations in response to decadal fluctuations in hydroclimatic conditions. Simulations of water levels at the index location used in the Bayesian model under alternative water management scenarios allow the posterior probability distributions of the number of foraging birds to be compared, thus providing a mechanism for linking management schemes to seasonal rainfall forecasts.
  • Microbial ecology, activity and abundance of aerobic in engineered drinking water and wastewater systemsHongkeun Park | Columbia University dissertation, 2011 [+]
    Abstract: Bacterial communities constitute one of the principal drivers for engineered technologies and processes in water and wastewater treatment. Over the past decade or so, using advanced molecular biology techniques, it has become possible to interrogate these engineered systems to determine the identity of the main microbial protagonists therein. In this dissertation research, the application of these techniques has been extended to develop molecular biomarkers that specifically examine the microbial ecology, activity and abundance of aerobic and anaerobic ammonia oxidizing bacteria in engineered drinking water and wastewater systems. The overall goals of this dissertation research were (1) to develop and apply molecular biomarkers that link microbial community structure and activity to anaerobic ammonium oxidation (anammox) process performance in a 2-stage bioreactor fed with actual anaerobic digestion centrate from a full-scale operational wastewater treatment facility in New York City, and (2) to investigate the suitability of molecular biomarkers for monitoring nitrification episodes and to examine the impact of alternating chloramination-chlorination over two consecutive years on the microbial ecology and abundance of AOB in a drinking water system. Based on these studies, it was possible to successfully link the microbial ecology, gene expression and N-removal in the test anaerobic ammonia oxidation (anammox) bioreactor. The 'predictive' potential of molecular biomarkers based on expression of hydrazine oxidoreductase and the intergenic spacer region of the 16S-23S ribosomal RNA genes was also demonstrated. Further, it was shown that reactor operating strategies contribute more to the microbial ecology of anammox reactors than the inocula to these reactors themselves. Using similar techniques and biomarkers, the presence of novel ammonia oxidizing bacteria was discovered in a full-scale drinking watershed, subjected to alternating chloramination-chlorination. Additionally, it was determined that freechlorination did not have long-term impacts on the population size or structure of the ammonia oxidizing bacteria. Therefore, alternate strategies for chlorine and chloramine based drinking water disinfection have been suggested.
  • Alcohol dehydrogenase expression as a biomarker of denitrification activity in activated sludge using methanol and glycerol as electron donorsHuijie Lu, Farhan Nuruzzaman, Janani Ravindhar and Kartik Chandran | Environmental Microbiology, 2011 [+]
    Abstract: Carbon sources such as methanol and glycerol are used for enhancing denitri?cation at wastewater treatment plants, which are required to meet increasingly stringent effluent nitrogen limits. Consequently, dosing strategies for these compounds could benefit from the development and application of molecular activity biomarkers to infer and distinguish between methanol- or glycerol-based denitrification in activated sludge. In this study, the applicability of genes coding for methanol dehydrogenase (mdh2 and mxaF) and glycerol dehydrogenase (dhaD) as potential biomarkers of denitri?cation activity using these specific substrates was explored and con?rmed using a two-pronged approach. First, during shortterm spikes of activated sludge biomass with glycerol, the ability of dhaD mRNA concentrations to closely track nitrate depletion profiles was demonstrated. Second, a high-degree of correlation of the mRNA concentrations of mdh2, mxaF and dhaD with methanol- and glycerol-based denitrification kinetics during long-term bioreactor operation using these substrates was also shown. Based on these results, expression of mdh2, mxaF and dhaD genes are promising biomarkers of in situ denitrification activity on methanol and glycerol, respectively, in mixed-culture engineered wastewater treatment processes.
  • Visionary Reflections from a Crystal Clear Pool of Water ScientistsUpmanu Lall | Journal of contemporary water research & education, 2011 [+]
    Abstract: Water, an essential resource, seems to be headed for unprecedented prominence in the public eye and as a field of scientific inquiry. Given its many spheres of influence and interaction (Fig. 1), this is hardly surprising, as we ponder scarcity induced by growing population, intensification of use, changing climate, and by the modification of the natural setting. The sustainable development and use of water and the environment are recognized as the key to reducing poverty, and societal vulnerability to the vagaries of nature. Many, many initiatives for water research and its application in a societal context are being advanced in the United States and worldwide by various groups of scientists and research agencies. While there is broad consensus on the importance of water research and the major areas of inquiry at least in the United States, consensus on a strategy for funding and managing water research appears to be emerging rather slowly, despite direct and significant efforts by the National Science Foundation and leading scientists. Funding levels for coordinated basic and applied research consequently continue to languish well below what one would expect for a scientific field of this size and importance. The diversity of needs represented by the field presents a massive opportunity, but may also inhibit the ability to clearly identify and prioritize a non-controversial research program on a limited budget. An interpretation of this socio-cultural dilemma is presented here in the context of the developments behind the formation of the Consortium of Universities for the Advancement of Hydrologic Science (CUAHSI), an organization dedicated to improving the state of research associated with the hydrologic and associated material cycles.
  • Irrigation Research with Sunflowers in KansasFreddie R. Lamm, Robert M. Aiken, Abdrabbo A Shehata Aboukheira | 23rd Annual Central Plains Irrigation Conference, 2011 [+]
    Abstract: Sunflower is a crop of interest in the Ogallala Aquifer region because of its shorter growing season and thus lower overall irrigation needs. Sunflowers are thought to better withstand short periods of crop water stress than corn and soybeans and the timing of critical sunflower water needs is also displaced from those of corn and soybeans. Thus, sunflowers might be a good choice for marginal sprinkler systems and for situations where the crop types are split within the center pivot sprinkler land area.
  • Left High and Dry? Climate Change, Common-Pool Resource Theory, and Adaptability of Western Water CoEdella Schlager, Tanya Heikkila | Public Administration Review, 2011 [+]
    Abstract: Efforts to reduce greenhouse gas emissions are falling far short of what a consensus of scientists argues is necessary to avoid potentially catastrophic increases in the mean global temperature. Increasingly, attention is devoted to understanding the vulnerability and adaptability of social and ecological systems to climate change in particular areas of the world. In the Western United States and other semi-arid regions of the world, possibly the most immediate, direct impacts of climate change involve the availability of water resources. Scientific evidence suggests that the West is likely to become hotter and drier and will experience greater variability in precipitation. These changes will affect tens of millions of residents in Western states, and nearly every sector of the economy, especially agriculture. The logic of commonpool resource theory is applied in this theory to assess the vulnerability and adaptability to climate change of interstate river compacts and to offer recommendations for coping with climate change. Future areas of research on this critical topic are also outlined.
  • Comparison of Partial and Full Nitrification Processes Applied for Treating High-Strength Nitrogen...Joon Ho Ahn, Tiffany Kwan, and Kartik Chandran | Environmental Science & Technology, 2011 [+]
    Abstract: The goal of this study was to compare the microbial ecology, gene expression, biokinetics, and N2O emissions from a lab-scale bioreactor operated sequentially in full-nitrification and partial-nitrification modes. Based on sequencing of 16S rRNA and ammonia monooxygenase subunit A (amoA) genes, ammonia oxidizing bacteria (AOB) populations during full- and partial-nitrification modes were distinct from one another. The concentrations of AOB (XAOB) and their respiration rates during full- and partial-nitrification modes were statistically similar, whereas the concentrations of nitrite oxidizing bacteria (XNOB) and their respiration rates declined significantly after the switch from full- to partial-nitrification. The transition from fullnitrification to partial nitrification resulted in a protracted transient spike of nitrous oxide (N2O) and nitric oxide (NO) emissions, which later stabilized. The trends inN2OandNOemissions correlated well with trends in the expression of nirK and norB genes that code for the production of these gases in AOB. Both the transient and stabilized N2O and NO emissions during partial nitrification were statistically higher than those during steady-state full-nitrification. Based on these results, partial nitrification strategies for biological nitrogen removal, although attractive for their reduced operating costs and energy demand, may need to be optimized against the higher carbon foot-print attributed to their N2O emissions.
  • Decadal predictions in demandMark A. Cane | Nature Geoscience, 2010 [+]
    Abstract: Decision makers are in need of decadal climate forecasts, for example, to help plan infrastructure investments. When — or whether — climate modellers will be able to deliver is not yet clear.
  • Scale invariance of water stress and scarcity indicators: Facilitating cross-scale comparisons ...Shama Perveen and L. Allan James | Applied Geography , 2010 [+]
    Abstract: Several indicators are commonly used to measure the degree of water resources vulnerability (e.g., water stress and scarcity) in different populations and regions. Little is known, however, about how these indicators respond to changes in the scale of data used to derive them. Two of the most widely used water resources vulnerability metrics, conventionally computed for mean annual values at the country level are Falkenmark Index (FI) for per capita water availability and the Criticality Ratio (CR) for water use to availability. This study computes FI and CR values at a wide range of scales and tests for trends with scale in three river basins: Missouri (North America), Danube (Europe) and Ganges (South Asia) Basins. Gridded sub-continental hydro-climatic data sets at 0.5  resolution are used and aggregated at multiple scales from 0.5  to 5.0  . Analytical logic and empirical evidence show that mean grid-cell values of these vulnerability metrics are in fact scale-independent (scale-invariant) for a given basin. When unscaled variables like water availability and use are ratioed to variables that depend on area, such as population, their dependency on scale may be lost and they become spatially scaled variables. For example, grid-cell mean values of water availability are scale dependent, but grid-cell mean values of the ratio of water availability to population (i.e. FI) are not. This implies that, for a particular river basin, average water resources vulnerability computed by FI and CR at one scale should apply to all scales. This has tremendous implications to applied geographic studies of water resources, and is especially interesting since the unscaled variables used to derive the two indices are scale dependent and vary greatly with scale. The paper and ?ndings highlight the multi-scale complexities of water resources and the geographic nature of water resources and vulnerability metrics.
  • Propensity of activated sludge to amplify or attenuate tetracycline resistance genes and ...Sungpyo Kim, Hongkeun Park, Kartik Chandran | Chemosphere, 2010 [+]
    Abstract: The overall goal of this study was to quantify the propensity of the activated sludge (AS) process at three wastewater treatment plants (WWTP) to amplify or attenuate tetracycline resistant bacteria (TRB) and tetracycline resistance genes (TRG). Accordingly, the abundance and fraction of TRB and seven TRG in different unit operations of these WWTP were analytically measured and modeled using a mass balance approach widely used for AS design. Based on the model, the AS process of the different WWTP neither amplified nor attenuated the TRB and TRG fractions. Of the TRG tested, the ribosomal protection genes, tet(O) and tet(W) were the most abundant, along the treatment train of the WWTP, on all sampling dates and sampling locations. Significant amounts of TRB and TRG were discharged in the effluent streams. Notably, in selected samples, the fraction of TRB increased in response to ultraviolet disinfection of treated wastewater compared to chlorination. This study therefore implicates wastewater treatment processes as significant point sources of tetracycline resistance determinants to the environment, and provides a mathematical basis to compute the production capacity of these determinants in the AS process.
  • Spatial scaling in a changing climate: A hierarchical bayesian model for non-stationary ...Carlos H.R. Lima, Upmanu Lall | Journal of Hydrology, 2010 [+]
    Abstract: Several studies have shown that statistics of streamflow time series, in particular empirical moments, scale with physical properties of the drainage basin, such as the catchment area. Those scaling laws have been extensively used to estimate statistics of streamflow series at ungauged sites. The role of climate variability and change has not been considered in such models. Further, most studies are based on classical statistics, where parameter uncertainties are usually neglected or not formally considered. In this paper we develop and apply hierarchical Bayesian models, to both assess regional and at-site trends in time in a spatial scaling framework, and simultaneously provide a rigorous framework for assessing and reducing parameter and model uncertainties. The models are tested with reconstructed natural inflow series from over 40 hydropower sites in Brazil with catchments areas varying from 2588 to 823,555 km2 . Both annual maximum flood series and monthly stream?ow are considered. Cross-validated results show that the Hierarchical Bayesian models are able to skillfully estimate monthly and flood flow probability distribution parameters for sites that were not used in model fitting. The models developed can be used to provide record augmentation at sites that have short records, or to estimate flow at ungauged sites, even in the absence of an assumption of time stationarity. Since model uncertainties are accounted for, the precision of the estimates can be quantified and hypotheses tests for regional and at-site trends can be formally made. A formal inclusion of climate predictors to facilitate seasonal forecasting or climate change scenario development is also feasible. This is indicated, but not developed here.
  • Mechanisms and Specific Directionality of Autotrophic Nitrous Oxide and Nitric Oxide Generation ...Ran Yu, Marlies J. Kampshreur, Mark C. M. Van Loosdrecht, and Kartik Chandran | Environmental Science and Technology, 2010 [+]
    Abstract: The overall goal of this study was to determine the molecular and metabolic responses of chemostat cultures of model nitrifying bacteria to imposition of and recovery from transient anoxic conditions. Based on the study, a specific directionality in nitrous oxide (N2O) and nitric oxide (NO) production was demonstrated. N2O production was only observed during recovery to aerobic conditions after a period of anoxia and correlated positively with the degree of ammonia accumulation during anoxia. NO, on the other hand, was emitted mainly under anoxia. The production of NO was linked to a major imbalance in the expression of the nitrite reductase gene, which was overexpressed during transient anoxia. In contrast, genes coding for ammonia and hydroxylamine oxidation and nitric oxide reduction were generally under-expressed during transient anoxia. These results are different from the observed parallel expression and activity of nitrite and nitric oxide reductase in heterotrophic bacteria subjected to transient oxygen cycling. Unlike NO, the production of N2O could not be solely correlated to gene expression patterns and likely involved responses at the enzyme activity or metabolic levels. Based on experimental data, the propensity of the nitrifying cultures for N2O production is related to a shift in their metabolism from a low specific activity (q < qmax) toward the maximum specific activity (qmax).
  • Local Polynomial Based Flood Frequency Estimator for Mixed PopulationSomkiat Apipattanavis, Balaji Rajagopalan, and Upmanu Lall | Journal of Hydrologic Engineering, 2010 [+]
    Abstract: Floods are often generated by more than one physical mechanism, e.g., rainfall and snowmelt. Consequently, traditional flood frequency methods that use a single distribution may not adequately describe the observed flood variability. Mixed distribution models have been proposed but they have two major drawbacks when applied to observed data: 1 determining the appropriate number of components or flood mechanisms and 2 identifying the probability distribution to be used for each component. Further, available ?ood data are often not sufficient for detecting mixture populations. As a result, mixed-distribution models can be dif?cult to apply in practice. In this paper we present a nonparametric approach based on local polynomial regression for estimating a flood quantile function that is data driven, flexible, and can capture any arbitrary features present in the data, enabling to alleviate the drawbacks of the traditional methods. We applied the proposed method to a suite of synthetic data from mixture of conventional distributions and to flood records that exhibit mixed population characteristics from Gila River basin of southeast and central Arizona. It is found that the proposed method provides a better fit to both the synthetic and historical data. Although, the proposed method is presented in the context of mixed population flood frequency estimation, the data-driven nature of the method lends itself as a simple, robust, and attractive alternative to traditional flood frequency estimation.
  • Sunflower, Soybean, and Grain Sorghum Crop Production as Affected by Dripline DepthF.R. Lamm, A.A. Aboukheira, T.P. Trooien | Applied Engineering in Agriculture , 2010 [+]
    Abstract: A 5-year field study (2004-2008) using irrigation water from an unlined surface reservoir was conducted to examine the effect of dripline depth (0.2, 0.3, 0.4, 0.5, or 0.6 m) on subsurface drip-irrigated rotational crop production of sunflower, soybean, and grain sorghum on a deep silt loam soil in western Kansas. Additional years (1999-2003) of data were included in the analysis of long-term dripline flowrates as affected by dripline depth. Crop seed germination and plant establishment with the subsurface drip irrigation system was not examined in this field study. There were no significant differences in crop yields or yield components in any year of the study with the exception of the number of soybean pods/plant in 2007. In that year, the number of pods/plant was significantly greater for the deeper dripline depths, but this improvement was not reflected in significantly greater soybean yield due to compensation from the other yield components. Measured crop water use and calculated water productivity (yield/water use) also were not significantly affected by dripline depth for any crop in any year. Crop water use varied less than 4% and water productivity varied less than 8% with dripline depth from the mean values for a given crop within a given year, but water productivity tended to be greater for the intermediate 0.4 m dripline depth. There was a tendency for the deeper dripline depths to have greater amounts of plant available soil water and this tendency was stronger as the crop season progressed and for deeper portions of the crop root zone. However, there were neither significant differences in plant available soil water in the upper (0 to 0.9 m) and lower root zones (0.9 to 2.4 m) at physiological maturity of the crop in any year, nor in the total 2.4 m soil profile. The lack of significant differences in crop yields, water use, water productivity and plant available soil water at physiological maturity suggests that dripline depths ranging from 0.2 to 0.6 m are acceptable for crop production of these three crops on the silt loam soils of the region. Measurements of plot dripline flowrates during the period 1999 through 2008 indicated a tendency for deeper driplines to have reduced flowrates and these flowrate reductions were statistically significant in 2001, 2006, 2007, and 2008. Although the reason for these plot flowrate reductions cannot be fully ascertained, it seems likely they were caused by emitter clogging related to an interaction between dripline depth and irrigation water quality for which the rationale was not determined.
  • Optimal Reservoir Operation for Flood Control Using Folded Dynamic ProgrammingD. Nagesh Kumar, Falguni Baliarsingh, K. Srinivasa Raju | Water Resources Management, 2010 [+]
    Abstract: Folded Dynamic Programming (FDP) is adopted for developing optimal reservoir operation policies for flood control. It is applied to a case study of Hirakud Reservoir in Mahanadi basin, India with the objective of deriving optimal policy for flood control. The river flows down to Naraj, the head of delta where a major city is located and finally joins the Bay of Bengal. As Hirakud reservoir is on the upstream side of delta area in the basin, it plays an important role in alleviating the severity of the flood for this area. Data of 68 floods such as peaks of inflow hydrograph, peak of outflow from reservoir during each flood, peak of flow hydrograph at Naraj and d/s catchment contribution are utilized. The combinations of 51, 54, 57 thousand cumecs as peak inflow into reservoir and 25.5, 20, 14 thousand cumecs respectively as peak d/s catchment contribution form the critical combinations for flood situation. It is observed that the combination of 57 thousand cumecs of inflow into reservoir and 14 thousand cumecs for d/s catchment contribution is the most critical among the critical combinations of flow series. The method proposed can be extended to similar situations for deriving reservoir operating policies for flood control.
  • Role of tropical Pacific SSTs in global medieval hydroclimate: A modeling studyRobert Burgman, Richard Seager, Amy Clement, and Celine Herweijer | Geophysical Research Letters, 2010 [+]
    Abstract: The role of tropical Pacific SSTs in driving global medieval hydroclimate is assessed. Using fossil coral records from Palmyra Atoll, tropical Pacific sea surface temperature (SST) boundary conditions are derived for the period 1320–1462 A.D. These boundary conditions consist of La Niña-like mean state conditions in the tropical Pacific with inter-annual and decadal variability about that altered state. The reconstructed SSTs in the tropical Pacific are used to force a 16 member ensemble of atmospheric general circulation model (AGCM) simulations, coupled to a one layer ocean model outside of the tropical Pacific. The AGCM simulations of medieval climate are compared with modern climate simulations for the period 1856–2005 A.D. and are shown to reproduce many aspects of medieval hydroclimate found in paleo-proxy records for much of the Western Hemisphere, northern Eurasia, and the northern tropics. These results suggest that many features of global medieval hydroclimate changes can be explained by changes in tropical Pacific SSTs, though the potential role for other oceans is also discussed.
  • Potential Security Implications of Environmental Change in Central AsiaTobias Siegfried | China and Eurasia Forum Quarterly, 2010 [+]
    Abstract: There exists a general consensus that future climate change has the potential to severely impact fragile regions on the planet, especially the semi-arid to arid zones [1]. If adaptation strategies are absent and institutions are not in place for mitigation, economies will suffer and intra- and interstate conflicts over the allocation of scarce resources will potentially ensue. These developments, together with growing population pressures, have the potential to increase social tensions and cause a dramatic deterioration of the security situation at watershed scales and beyond [2] (see Figure 1). Central Asia, in particular, is one of the regions vulnerable to environmental change. Central Asia is a landlocked region of some 4 million square kilometers with 80 million inhabitants, a mere 2 percent of Asia’s population. Yet it sits astride $3 trillion of fossil fuels and remains a strategic crossroads at which the interests and influences of foreign lands meet. The five Central Asian republics crucially depend on the availability of sufficient amounts of annual renewable freshwater for hydropower production in the upstream and for irrigated agriculture in the downstream. The degree of water’s importance to the region is a simple matter of geography and climate. Central Asia is arid except for the mountainous regions of Kyrgyzstan and Tajikistan, where annual precipitation feeds the region’s major rivers, the Amu and Syr Darya. It was these rivers, and the Aral Sea into which they drained, that drew in the Soviet Union in the 1920s. Central Asia’s last foreign overlords, the Soviets produced 20,000 miles of canals, 45 dams, and 80 reservoirs, providing water for agriculture and industry. The system was centrally controlled from Moscow until 1991, after which a group of untested national governments was forced to manage what had been a unitary economic system untroubled by largely factitious borders.
  • Dynamic nonpoint-source pollution control policy: ambient transfers and uncertaintyStergios Athanassoglou | Journal of Economic Dynamics and Control, 2010 [+]
    Abstract: When a regulator cannot observe or infer individual emissions, corrective policy must rely on ambient pollution data. Assuming this kind of environment, we study a class of di fferential games of pollution control with pro t functions that are polynomial in the global pollution stock. Given an open-loop emissions strategy satisfying mild regularity conditions, an ambient transfer scheme is exhibited that induces it in Markov-perfect equilibrium (MPE). Proposed transfers are a polynomial function of the diff erence between actual and desired pollution levels; moreover, they are designed so that in MPE no tax or subsidy is ever levied. Their applicability under stochastic pollution dynamics is studied for a symmetric game of polluting oligopolists with linear demand. We discuss a quadratic scheme that induces agents to adopt Markovian emissions strategies that are stationary and linearly decreasing in total pollution. Total expected ambient transfers are non-positive and their magnitude is linearly increasing in physical volatility, the size of the economy, and the absolute value of the slope of the inverse demand function. How- ever, if the regulator is interested in inducing a constant emissions strategy then, in expectation, transfers vanish. The total expected ambient transfer is compared to its point-source equivalent.
  • Factors Promoting Emissions of Nitrous Oxide and Nitric Oxide From Denitrifying Sequencing Batch ...Huijie Lu and Kartik Chandran | Biotechnology and Bioengineering, 2010 [+]
    Abstract: The emissions of nitrous oxide (N2O) and nitric oxide (NO) from biological nitrogen removal (BNR) operations via nitrification and denitri?cation is gaining increased prominence. While many factors relevant to the operation of denitrifying reactors can influence N2O and NO emissions from them, the role of different organic carbon sources on these emissions has not been systematically addressed or interpreted. The overall goal of this study was to evaluate the impact of three factors, organic carbon limitation, nitrite concentrations, and dissolved oxygen concentrations on gaseous N2O and NO emissions from two sequencing batch reactors (SBRs), operated, respectively, with methanol and ethanol as electron donors. During undisturbed ultimate-state operation, emissions of both N2O and NO from either reactor were minimal and in the range of <0.2% of influent nitrate-N load. Subsequently, the two reactors were challenged with transient organic carbon limitation and nitrite pulses, both of which had little impact on N2O or NO emissions for either electron donor. In contrast, transient exposure to oxygen led to increased production of N2O (up to 7.1% of influent nitrate-N load) from ethanol grown cultures, owing to their higher kinetics and potentially lower susceptibility to oxygen inhibition. A similar increase in N2O production was not observed from methanol grown cultures. These results suggest that for dissolved oxygen, but not for carbon limitation or nitrite exposure, N2O emission from heterotrophic denitrification reactors can vary as a function of the electron donor used.
  • Adjustment of the atmospheric circulation to tropical Pacific SST anomalies: Variability of ...R. Seager, N. Naik, M. Ting, M. A. Cane, N. Harnik, and Y. Kushnir | Quarterly Journal of the Royal Meteorological Society , 2010 [+]
    Abstract: El Nino–Southern Oscillation (ENSO) related precipitation anomalies in North America are related to changes in the paths of storm systems across the Pacific Ocean, with a more southern route into southwestern North America during El Ninos and ˜ a more northern route into the Pacific Northwest during La Ninas. Daily reanalysis ˜ data are analyzed to confirm these changes. Seasonal mean upper tropospheric eddy statistics show, for El Ninos (La Ni ˜ nas), a pattern that is shifted southward ˜ (northward) compared with climatology. Paths of coherent phase propagation of transient eddies and of the propagation of wave packets are analyzed. A coherent path of propagation across the Pacific towards North America is identified that is more zonal during El Nino winters and, during La Ni ˜ nas, has a dominant path heading ˜ northeastward to the Pacific Northwest. A second path heading southeastward from the central Pacific to the tropical east Pacific is more accentuated during La Ninas than El Ni ˜ nos. These changes in wave propagation are reproduced in an ˜ ensemble of seasonal integrations of a general circulation model forced by a tropical Pacific sea-surface temperature pattern, confirming that the changes are forced by changes in the mean atmospheric state arising from changes in tropical sea-surface temperature. A simplified model with a specified basic state is used to model the storm tracks for El Nino and La Ni ˜ na winters. The results suggest that the changes in transient eddy propagation and the eddy statistics can be understood in terms of the refraction of transient eddies within different basic states.
  • A moist model monsoonMark A. Cane | Nature, 2010 [+]
    Received wisdom about the main driver of the South Asian monsoon comes into question with a report that tests the idea that the Himalayas, not the Tibetan plateau, are the essential topographic ingredient.
  • Improved water allocation utilizing probabilistic climate forecasts: Short-term water contracts ...A. Sankarasubramanian, Upmanu Lall, Francisco Assis Souza Filho, and Ashish Sharma | Water Resources Research, 2009 [+]
    Abstract: Probabilistic, seasonal to interannual streamflow forecasts are becoming increasingly available as the ability to model climate teleconnections is improving. However, water managers and practitioners have been slow to adopt such products, citing concerns with forecast skill. Essentially, a management risk is perceived in ‘‘gambling’’ with operations using a probabilistic forecast, while a system failure upon following existing operating policies is ‘‘protected’’ by the official rules or guidebook. In the presence of a prescribed system of prior allocation of releases under different storage or water availability conditions, the manager has little incentive to change. Innovation in allocation and operation is hence key to improved risk management using such forecasts. A participatory water allocation process that can effectively use probabilistic forecasts as part of an adaptive management strategy is introduced here. Users can express their demand for water through statements that cover the quantity needed at a particular reliability, the temporal distribution of the ‘‘allocation,’’ the associated willingness to pay, and compensation in the event of contract nonperformance. The water manager then assesses feasible allocations using the probabilistic forecast that try to meet these criteria across all users. An iterative process between users and water manager could be used to formalize a set of short-term contracts that represent the resulting prioritized water allocation strategy over the operating period for which the forecast was issued. These contracts can be used to allocate water each year/season beyond long-term contracts that may have precedence. Thus, integrated supply and demand management can be achieved. In this paper, a single period multiuser optimization model that can support such an allocation process is presented. The application of this conceptual model is explored using data for the Jaguaribe Metropolitan Hydro System in Ceara, Brazil. The performance relative to the current allocation process is assessed in the context of whether such a model could support the proposed short-term contract based participatory process. A synthetic forecasting example is also used to explore the relative roles of forecast skill and reservoir storage in this framework.
  • Early 21st-Century Drought in MexicoD. Stahle, E. Cook, J. Diaz, F. Fye, D. Burnette, R. Griffin, R. Soto, R. Seager, and R. Heim, Jr. | Eos, Transactions, American Geophysical Union, 2009 [+]
    Abstract: Prolonged drought conditions have persisted over western North America since at least 1999, affecting snowpack, stream discharge, reservoir levels, and wildfire activity [Mote et al., 2005; Westerling et al., 2006; MacDonald et al., 2008]. Instrumental precipitation, temperature, and Palmer Drought Severity Indices (PDSI) indicate that severe and sustained drought began in 1994 in Mexico, where it has continued with only limited relief for the past 15 years. This late twentieth- and early 21st-century Mexican drought (referred to below as the “early 21st-century drought”) has equaled some aspects of the 1950s drought, which is the most severe drought evident in the instrumental climate record for Mexico (1900–2008). Large-scale changes in ocean-atmospheric circulation have contributed to the lower than normal precipitation that has led to the current drought [Seager, 2007], but global warming and the sharp regional warming across Mexico, which appears to have been aggravated by land cover changes [Englehart and Douglas, 2005], may have added an anthropogenic component to the early 21st-century drought.
  • Seasonal and annual maximum streamflow forecasting using climate information: applied to ...Hyun-Han Kwon, Casey Brown, Kaiqin Xu, & Upmanu Lall | Hydrological Sciences, 2009 [+]
    Abstract: This paper explores the potential for seasonal prediction of hydrological variables that are potentially useful for reservoir operation of the Three Gorges Dam, China. The seasonal flow of the primary inflow season and the peak annual flow are investigated at Yichang hydrological station, a proxy for inflows to the Three Gorges Dam. Building on literature and diagnostic results, a prediction model is constructed using sea-surface temperatures and upland snow cover available one season ahead of the prediction period. A hierarchical Bayesian approach is used to estimate uncertainty in the parameters of the prediction model and to propagate these uncertainties to the predictand. The results show skill for both the seasonal flow and the peak annual flow. The peak annual flow model is then used to estimate a design flood (50-year flood or 2% exceedence probability) on a year-to-year basis. The results demonstrate the inter-annual variability in flood risk. The predictability of both the seasonal total inflow and the peak annual flow (or a design flood volume) offers potential for adaptive management of the Three Gorges Dam reservoir through modification of the operating policy in accordance with the year-to-year changes in these variables.
  • Toya Irrigation Socio-economic StudyMillennium Villages Project: Alpha Oumar Kergna, Mamadou Kabirou N'Diaye, 2009 [+]
    In 2009, the Millennium Villages Project completed a socio-economic study of the Toya, Mali, region and the feasibility of using irrigated agriculture to improve livelihoods and decrease poverty and hunger. They conclude that there is great potential for increasing irrigated agriculture but much support is needed. Recommendations for types and methods of support are given.
  • River Flood Forecasting Using Complementary Muskingum Rating EquationsParthasarathi Choudhury and A. Sankarasubramanian | Journal of Hydrologic Engineering, 2009 [+]
    Abstract: : A model for real-time flood forecasting in river systems with large drainage areas has been developed. Flow variations between upstream and downstream stations are interlinked and are typically governed by reach properties. Unique paired variations establish useful flow correspondence resulting in inflow and outflow forecasting models for a reach. The proposed model can generate forecasts with increased lead time without applying a separate inflow forecasting model and can also provide updated forecasts essential for real-time applications. The model was applied to flood forecasting in Tar River Basin, N.C., covering a drainage area of 13,921 km2 . The model aggregates multiple upstream flows to provide long range forecasts for two downstream stations in the basin. Applicability of the model in estimating complete upstream and downstream hydrographs was demonstrated using a textbook example. Application results indicate that the new model can provide complete and updatable evolution of hydrographs using the current ?ow state.
  • Mexican drought: an observational modeling and tree ring study of variability and climate changeR. Seager, M. Ting, M. Davis, M. Cane, N. Naik, J. Nakamura, C. Li, E. Cook, and D. W. Stahle | Atmosfera, 2009 [+]
    Abstract: Variability of Mexican hydroclimate, with special attention to persistent drought, is examined using observations, model simulations forced by historical sea surface temperature (SST), tree ring reconstructions of past climate and model simulations and projections of naturally and anthropogenically forced climate change. During the winter half year, hydroclimate across México is influenced by the state of the tropical Pacific Ocean with the Atlantic playing little role. Mexican winters tend to be wetter during El Niño conditions. In the summer half year northern México is also wetter when El Niño conditions prevail, but southern México is drier. A warm tropical North Atlantic Ocean makes northern México dry and southern México wet. These relationships are reasonably well reproduced in ensembles of atmosphere model simulations forced by historical SST for the period from 1856 to 2002. Large ensembles of 100 day long integrations are used to examine the day to day evolution of the atmospheric circulation and precipitation in response to a sudden imposition of a El Niño SST anomaly in the summer half year. Kelvin waves propagate east and immediately cause increased column-integrated moisture divergence and reduced precipitation over the tropical Americas and Intra-America Seas. Within a few days a low level high pressure anomaly develops over the Gulf of México. A forced nonlinear model is used to demonstrate that this low is forced by the reduced atmospheric heating over the tropical Atlantic-Intra-America Seas area. Tree ring reconstructions that extend back before the period of instrumental precipitation data coverage are used to verify long model simulations forced by historical SST. The early to mid 1950s drought in northern México appears to have been the most severe since the mid nineteenth century and likely arose as a response to both a multiyear La Niña and a warm tropical North Atlantic. A drought in the 1890s was also severe and appears driven by a multiyear La Niña alone. The drought that began in the 1990s does not exceed these droughts in either duration or severity. Tree ring records extending back to the fourteenth century suggest that the late sixteenth century megadrought may have been the longest drought to have ever affected México. While the last decade or so in north and central México has been drier than preceding decades, the associated continental pattern of hydroclimate change does not fit that which models project to occur as a consequence of rising greenhouse gases and global warming. However, models robustly predict that México will dry as a consequence of global warming and that this drying should already be underway. At least for now, in nature, this is likely obscured by strong natural atmosphere-ocean variability.
  • Simulation of daily rainfall scenarios with interannual and multidecadal climate cycles for ...Hyun-Han Kwon, Upmanu Lall, and Jayantha Obeysekera | Stochastic Environmental Research and Risk Assessment , 2009 [+]
    Abstract: Concerns about the potential effects of anthropogenic climate change have led to a closer examination of how climate varies in the long run, and how such variations may impact rainfall variations at daily to seasonal time scales. For South Florida in particular, the influences of the low-frequency climate phenomena, such as the El Nino Southern Oscillation (ENSO) and the Atlantic Multi-decadal Oscillation (AMO), have been identi?ed with aggregate annual or seasonal rainfall variations. Since the combined effect of these variations is manifest as persistent multi-year variations in rainfall, the question of modeling these variations at the time and space scales relevant for use with the daily time step-driven hydrologic models in use by the South Florida Water Management District (SFWMD) has arisen. To address this problem, a general methodology for the hierarchical modeling of low- and high-frequency phenomenon at multiple rain gauge locations is developed and illustrated. The essential strategy is to use long-term proxies for regional climate to first develop stochastic scenarios for regional climate that include the low-frequency variations driving the regional rainfall process, and then to use these indicators to condition the concurrent simulation of daily rainfall at all rain gauges under consideration. A newly developed methodology, called Wavelet Autoregressive Modeling (WARM), is used in the ?rst step after suitable climate proxies for regional rainfall are identified. These proxies typically have data available for a century to four centuries so that long-term quasi-periodic climate modes of interest can be identified more reliably. Correlation analyses with seasonal rainfall in the region are used to identify the specific proxies considered as candidates for subsequent conditioning of daily rainfall attributes using a Non-homogeneous hidden Markov model (NHMM). The combined strategy is illustrated for the May–June–July (MJJ) season. The details of the modeling methods and results for the MJJ season are presented in this study.
  • Megadroughts in North America: placing IPCC projections of hydroclimatic change in a long-term ...E. R. Cook, R. Seager, R. R. Heim, Jr., R. S. Vose, C. Herweijer, and C. Woodhouse | Journal of Quaternary Science, 2009 [+]
    Abstract: IPCC Assessment Report 4 model projections suggest that the subtropical dry zones of the world will both dry and expand poleward in the future due to greenhouse warming. The US Southwest is particularly vulnerable in this regard and model projections indicate a progressive drying there out to the end of the 21st century. At the same time, the USA has been in a state of drought over much of the West for about 10 years now. While severe, this turn of the century drought has not yet clearly exceeded the severity of two exceptional droughts in the 20th century. So while the coincidence between the turn of the century drought and projected drying in the Southwest is cause for concern, it is premature to claim that the model projections are correct. At the same time, great new insights into past drought variability over North America have been made through the development of the North American Drought Atlas from tree rings. Analyses of this drought atlas have revealed past megadroughts of unprecedented duration in the West, largely in the Medieval period about 1000 years ago. A vastly improved Living Blended Drought Atlas (LBDA) for North America now under development reveals these megadroughts in far greater detail. The LBDA indicates the occurrence of the same Medieval megadroughts in the West and similar-scale megadroughts in the agriculturally and commercially important Mississippi Valley. Possible causes of these megadroughts and their implications for the future are discussed.
  • Impact of Varying Electron Donors on Molecular Microbial Ecology and Biokinetics Methylotrophic ...Vladimir Baytshtok, Huijie Lu, Hongkeun Park, Sungpyo Kim, Ran Yu, Kartik Chandran | Biotechnology and Engineering, 2009 [+]
    Abstract: The goal of this study was to identify bacterial populations that assimilated methanol in a denitrifying sequencing batch reactor (SBR), using stable isotope probing (SIP) of 13 C labeled DNA and quantitatively track changes in these populations upon changing the electron donor from methanol to ethanol in the SBR feed. Based on SIP derived 13 C 16S rRNA gene clone libraries, dominant SBR methylotrophic bacteria were related to Methyloversatilis spp. and Hyphomicrobium spp. These methylotrophic populations were quanti?ed via newly developed real-time PCR assays. Upon switching the electron donor from methanol to ethanol, Hyphomicrobium spp. concentrations decreased significantly in accordance with their obligately methylotrophic nutritional mode. In contrast, Methyloversatilis spp. concentrations were relatively unchanged, in accordance with their ability to assimilate both methanol and ethanol. Direct assimilation of ethanol by Methyloversatilis spp. but not Hyphomicrobium spp. was also confirmed via SIP. The reduction in methylotrophic bacterial concentration upon switching to ethanol was paralleled by a significant decrease in the methanol supported denitrification biokinetics of the SBR on nitrate. In sum, the results of this study demonstrate that the metabolic capabilities (methanol assimilation and metabolism) and substrate specificity (obligately or facultatively methylotrophic) of two distinct methylotrophic bacterial populations contributed to their survival or washout in denitrifying bioreactors.
  • Finescale Evaluation of Drought in a Tropical Setting: Case Study in Sri LankaBradfield Lyon, Lareef Zubair, Vidhura Ralapanawe, and ZeenasYahiya | Journal of Applied Meteorology and Climatology, 2009 [+]
    Abstract: In regions of climatic heterogeneity, finescale assessment of drought risk is needed for policy making and drought management, mitigation, and adaptation. The relationship between drought relief payments (a proxy for drought risk) and meteorological drought indicators is examined through a retrospective analysis for Sri Lanka (1960–2000) based on records of district-level drought relief payments and a dense network of 284 rainfall stations. The standardized precipitation index and a percent-of-annual-average index for rainfall accumulated over 3, 6, 9, and 12 months were used, gridded to a spatial resolution of 10 km. An encouraging correspondence was identified between the spatial distribution of meteorological drought occurrence and historical drought relief payments at the district scale. Time series of drought indices averaged roughly over the four main climatic zones of Sri Lanka showed statistically significant (p , 0.01) relationships with the occurrence of drought relief. The 9-month cumulative drought index provided the strongest relationships overall, although 6- and 12-month indicators provided generally similar results. Some cases of appreciable drought without corresponding relief payments could be attributed to fiscal pressures, as during the 1970s. Statistically significant relationships between drought indicators and relief payments point to the potential utility of meteorological drought assessments for disaster risk management. In addition, the study provides an empirical approach to testing which meteorological drought indicators bear a statistically significant relationship to drought relief across a wide range of tropical climates.
  • Real-time remote sensing driven river basin modeling using radar altimetryS. J. P. Cardenal, N. D. Riegels, P. A. M. Berry, R. G. Smith, A. Yakovlev, T. U. Siegfried, and ... | Journal of Hydrology, 2009 [+]
    Abstract: Remote sensing (RS) data are an alternative to in-situ hydrometeorological data in remote and poorly monitored areas and are increasingly used in hydrological modeling. This study presents a lumped, conceptual, river basin water balance modeling approach based entirely on RS data: precipitation was obtained from the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA), temperature from the European Centre for Medium-Range Weather Forecast (ECMWF) global reanalysis dataset and evapotranspiration was derived from temperature data. The Ensemble Kalman Filter was used to assimilate radar altimetry (ERS2 and Envisat) measurements of reservoir water surface elevations. The modeling approach is applied to the Syr Darya River Basin, a primarily snowmelt driven basin with large topographical variability and scarce meteorological data that is shared between 4 countries with conflicting water management interests. Assimilation of radar altimetry data improved model results significantly. Without data assimilation, model performance was limited, probably because of the size and complexity of the model domain, simplifications inherent in model design, and the uncertainty of RS data. Data assimilation reduced the mean of the reservoir water surface level residuals from 19.5 to 4.5 meters, and model root mean square error from 16.7 meters to 6.4 meters. By providing an impartial source of information about the hydrological system that can be updated in real time, the modeling approach described here could provide useful hydrological forecast information that could be updated at time scales appropriate for decision-making. The approach has potential to facilitate cooperation in transboundary basins with conflicting management objectives.
  • Forced and Internal Twentieth-Century SST Trends in the North AtlanticMingfang Ting, Yochanan Kushnir, Richard Seager, and Cuihua Li | Journal of Climate, 2009 [+]
    Abstract: In recent years, two alarming trends in North Atlantic climate have been noted: an increase in the intensity and frequency of Atlantic hurricanes and a rapid decrease in Greenland ice sheet volume. Both of these phenomena occurred while a significant warming took place in North Atlantic sea surface temperatures (SSTs), thus sparking a debate on whether the warming is a consequence of natural climate variations, anthropogenic forcing, or both; and if both, what their relative roles are. Here models and observations are used to detect and attribute long-term (multidecadal) twentieth-century North Atlantic (NA) SST changes to their anthropogenic and natural causes. A suite of Intergovernmental Panel on Climate Change (IPCC) twentieth-century (C20C) coupled model simulations with multiple ensemble members and a signal-to-noise maximizing empirical orthogonal function analysis are used to identify a model-based estimate of the forced, anthropogenic component in NA SST variability. Comparing the results to observations, it is argued that the long-term, observed, North Atlantic basin-averaged SSTs combine a forced global warming trend with a distinct, local multidecadal ‘‘oscillation’’ that is outside of the range of the model-simulated, forced component and most likely arose from internal variability. This internal variability produced a cold interval between 1900 and 1930, followed by 30 yr of relative warmth and another cold phase from 1960 to 1990, and a warming since then. This natural variation, referred to previously as the Atlantic Multidecadal Oscillation (AMO), thus played a significant role in the twentieth-century NA SST variability and should be considered in future, near-term climate projections as a mechanism that, depending on its behavior, can act either constructively or destructively with the region’s response to anthropogenic influence, temporarily amplifying or mitigating regional climate change.
  • Hydroclimatic influence of large-scale circulation on the variability of reservoir inflowRajib Maity and D. Nagesh Kumar | Hydrological Processes, 2009 [+]
    Abstract: In this study, the nature of basin-scale hydroclimatic association for Indian subcontinent is investigated. It is found that, the large-scale circulation information from Indian Ocean is also equally important in addition to the El Nino-Southern Oscillation ˜ (ENSO), owing to the geographical location of Indian subcontinent. The hydroclimatic association of the variation of monsoon inflow into the Hirakud reservoir in India is investigated using ENSO and EQUatorial INdian Ocean Oscillation (EQUINOO, the atmospheric part of Indian Ocean Dipole mode) as the large-scale circulation information from tropical Pacific Ocean and Indian Ocean regions respectively. Individual associations of ENSO & EQUINOO indices with in?ow into Hirakud reservoir are also assessed and found to be weak. However, the association of inflows into Hirakud reservoir with the composite index (CI) of ENSO and EQUINOO is quite strong. Thus, the large-scale circulation information from Indian Ocean is also important apart form the ENSO. The potential of the combined information of ENSO and EQUINOO for predicting the inflows during monsoon is also investigated with promising results. The results of this study will be helpful to water resources managers due to fact that the nature of monsoon inflow is becoming available as an early prediction.
  • Identifying uncertainty and defining risk in the context of the WWDR-4Kye Mesa Baroang, Molly Hellmuth, and Paul Block | United Nations World Water Assessment Program, 2009 [+]
    Abstract: Changes and the uncertainties associated with them are critical to our relationship with water and water resources. Some changes within human and natural systems result in negative consequences and increase risk, while others may have positive effects that reduce risk. We make decisions under uncertain conditions and try to manage these risks. Given the inherently stochastic nature of water systems and drivers, water resources professionals have essentially always been addressing issues of uncertainty and risk. However, as systems undergo fundamental changes and become increasingly complex and interwoven, it becomes even more difficult to make decisions and manage risks in water resources. As our knowledge increases and drivers of change impact water resources, assumptions of stationarity in climatic and hydrologic systems are called into question. The purpose of this paper is to help establish a common understanding and acceptable definitions of risk and uncertainty in the broader context of water resources, their use and management. After beginning with an exploration of the various elements and sources of uncertainty, we outline some of the key definitions and conceptions of risk. The paper then explores the application of uncertainty and risk in the context of water resources, with an emphasis on four water-related risks. We examine the role of key drivers identified in the 3rd World Water Development Report on these risks. This is followed by a brief history of the evolving approach to risk analysis, with references to applications in water resources and a discussion of the recent responses to addressing the uncertainties associated with nonstationarity. The paper concludes with a brief discussion of the recommended components of a comprehensive definition of risk that can help orient discussions of risk and management in water resources for the 4th World Water Development Report.
  • Effect of Land Cover Heterogeneity on Soil Moisture Retrieval Using Active Microwave Remote ...Tarendra Lakhankar, Hosni Ghedira, Marouane Temimi, Amir E. Azar, and Reza Khanbilvardi | Remote Sensing, 2009 [+]
    Abstract: This study addresses the issue of the variability and heterogeneity problems that are expected from a sensor with a larger footprint having homogenous and heterogeneous sub-pixels. Improved understanding of spatial variability of soil surface characteristics such as land cover and vegetation in larger footprint are critical in remote sensing based soil moisture retrieval. This study analyzes the sub-pixel variability (standard deviation of subgrid pixels) of Normalized Difference Vegetation Index and SAR backscatter. Backpropagation neural network was used for soil moisture retrieval from active microwave remote sensing data from Southern Great Plains of Oklahoma. The effect of land cover heterogeneity (number of different vegetation species within pixels) on soil moisture retrieval using active microwave remote sensing data was investigated. The presence of heterogeneous vegetation cover reduced the accuracy of the derived soil moisture using microwave remote sensing data. The results from this study can be used to characterize the uncertainty in soil moisture retrieval in the context of Soil Moisture Active and Passive (SMAP) mission which will have larger footprint.
  • Multiscale Effects on Spatial Variability Metrics in Global Water Resources DataShama Perveen and L. Allan James | Water Resources Management, 2009 [+]
    Abstract: Spatial scales and methods for dealing with scale have been widely discussed in the water resources literature. Different spatial processes operate at different scales so interpretations based on data from one scale may not apply to another. Understanding the behavior of phenomena at multiple-scales of data aggregation is thus imperative to accurate integrations of data and models at different geographic resolutions. This study tests theoretical concepts of scale by presenting empirical results of multiscale GIS and statistical analyses on gridded water-availability, water use and population data for the Danube Basin in Europe, with results corroborated by similar tests in the Ganges (South Asia) and Missouri (North America) Basins. Fine-resolution datasets were aggregated to coarser grid sizes and standard statistical measures of spatial variability were computed. Statistical analysis of spatial variability demonstrated two distinctly different cases for unscaled and scaled variables. Results show that variance (and standard deviation) in unscaled variables like freshwater supply, use and population increases at coarser scales—contrary to the common assumption of decreasing variability as grid-cell size increases. On the other hand, a decreasing trend in variability with scale is noted for variables scaled to area or population (like population density, water availability per capita etc.). Moreover, relationships between variability and scale show strong non-linear trends. No mention of these relationships has been found in the water resources or socio-economic literature for scale and variability. Regression analyses suggest that power functions are the most appropriate model to ?t trends in increasing variability at multiple scales. These results can be applied to interpretations of water-stress and water scarcity data and their locations relative to water sources or topographic barriers.
  • Microbial Mineral Weathering for Nutrient Acquisition Releases ArsenicB. J. Mailloux, E. Alexandrova, A. R. Keimowitz, K. Wovkulich, G. A. Freyer, M. Herron, ... | Applied and Environmental Microbiology, 2009 [+]
    Abstract: Tens of millions of people in Southeast Asia drink groundwater contaminated with naturally occurring arsenic. How arsenic is released from the sediment into the water remains poorly understood. Here, we show in laboratory experiments that phosphate-limited cells of Burkholderia fungorum mobilize ancillary arsenic from apatite. We hypothesize that arsenic mobilization is a by-product of mineral weathering for nutrient acquisition. The released arsenic does not undergo a redox transformation but appears to be solubilized from the apatite mineral lattice during weathering. Analysis of apatite from the source area in the Himalayan basin indicates the presence of elevated levels of arsenic, with an average concentration of 210 mg/kg. The rate of arsenic release is independent of the initial dissolved arsenic concentration and occurs at phosphate levels observed in Bangladesh aquifers. We also demonstrate the presence of the microbial phenotype that releases arsenic from apatite in Bangladesh aquifer sediments and groundwater. These results suggest that microbial mineral weathering for nutrient acquisition could be an important mechanism for arsenic mobilization.
  • A U.S. CLIVAR Project to Assess and Compare the Responses of Global Climate Models to Drought ...S. Schubert, David Gutzler, H. Wang, A. Dai, T. Delworth, C. Deser, K. Findell, R. Fu, ... | Journal of Climate , 2009 [+]
    Abstract: The U.S. Climate Variability and Predictability (CLIVAR) working group on drought recently initiated a series of global climate model simulations forced with idealized SST anomaly patterns, designed to address a number of uncertainties regarding the impact of SST forcing and the role of land–atmosphere feedbacks on regional drought. The runs were carried out with five different atmospheric general circulation models (AGCMs) and one coupled atmosphere–ocean model in which the model was continuously nudged to the imposed SST forcing. This paper provides an overview of the experiments and some initial results focusing on the responses to the leading patterns of annual mean SST variability consisting of a Pacifc El Nin˜o–Southern Oscillation (ENSO)-like pattern, a pattern that resembles the Atlantic multidecadal oscillation (AMO), and a global trend pattern. One of the key findings is that all of the AGCMs produce broadly similar (though different in detail) precipitation responses to the Pacific forcing pattern, with a cold Pacific leading to reduced precipitation and a warm Pacific leading to enhanced precipitation over most of the United States. While the response to the Atlantic pattern is less robust, there is general agreement among the models that the largest precipitation response over the United States tends to occur when the two oceans have anomalies of opposite signs. Further highlights of the response over the United States to the Pacific forcing include precipitation signal-to-noise ratios that peak in spring, and surface temperature signal-to-noise ratios that are both lower and show less agreement among the models than those found for the precipitation response. The response to the positive SST trend forcing pattern is an overall surface warming over the world’s land areas, with substantial regional variations that are in part reproduced in runs forced with a globally uniform SST trend forcing. The precipitation response to the trend forcing is weak in all of the models. It is hoped that these early results, as well as those reported in the other contributions to this special issue on drought, will serve to stimulate further analysis of these simulations, as well as suggest new research on the physical mechanisms contributing to hydroclimatic variability and change throughout the world.
  • North American Snow Depth and Climate Teleconnections PatternsYan Ge and Gavin Gong | Journal of Climate, 2009 [+]
    Abstract: Snow–atmosphere relationships have been studied for nearly half a century, but the primary focus has been on snow extent variability, largely because of the relative scarcity of snow depth data. A recently released North American snow depth dataset, with extensive spatial coverage and multidecadal temporal duration, provides a new opportunity to compare snow depth–climate relationships with snow extent–climate relationships over North America. Robust concurrent lead and lag correlations are observed between snow depth and two major climate modes, the Pacific decadal oscillation (PDO) and the Pacific–North America (PNA) pattern, across North America and throughout the snow season. In contrast, snow extent exhibits a less coherent relationship with PDO and PNA except in late spring, which can be interpreted as a residual of the snow depth–climate mode relationship. A regional signature for the snow depth–PDO/PNA relationship is also identified, centered over interior central-western North America. Smaller scales mask the regional effect of PDO and PNA because of local snow depth variability, while larger continental scales exceed the regional domain of the climate mode teleconnections. Overall these results suggest that North American snow depth variability may have greater climatic causes and consequences than snow extent. Physical mechanisms that may be responsible for the observed snow depth–climate teleconnection patterns such as the surface energy balance, moisture transport, and atmospheric flow regimes are briefly discussed.
  • Resolving Water Conflicts: A Comparative Analysis of Interstate River CompactsEdella Schlager and Tanya Heikkila | Policy Studies Journal, 2009 [+]
    Abstract: This paper examines compacts used by U.S. western states to engage in shared governance of interstate rivers. Compacts are viewed as inflexible, rigid governance structures incapable of responding to changing environmental and institutional settings because of the use of unanimity rules and the inability to directly regulate water users. Using data from a study of 14 western interstate river compacts we examine this claim. In particular, we explore the response of compacts to water con?icts. We find that members of compacts, closely related water agencies, and compact governments are capable of responding to conflicts. To better understand this finding, we identify the conditions under which compacts are likely to address conflicts, as well as the types of conflict solutions compact governments adopted.
  • Pacific Decadal Variability in the View of Linear Equatorial Wave TheoryJulien Emile-Geay, and Mark A. Cane | Journal of Physical Oceanography, 2009 [+]
    Abstract: It has recently been proposed, within the framework of the linear shallow-water equations, that tropical Pacific decadal variability (PDV) can be accounted for by basin modes with eigenperiods of 10 to 20 yr, amplifying a midlatitude wind forcing with an essentially white spectrum. Here the authors use a different formalism of linear equatorial wave theory. The Green’s function is computed for the wind-forced response of a linear equatorial shallow-water ocean and uses the earlier results of Cane and Moore to obtain a compact, closed form expression for the motion of the equatorial thermocline, which applies to all frequencies lower than seasonal. This expression is new and allows a systematic comparison of the effect of low- and high-latitude winds on the equatorial thermocline. At very low frequencies (decadal time scales), the planetary geostrophic solution used by Cessi and Louazel is recovered, as well as the equatorial wave solution of Liu, and a formal explanation for this convergence is given. Nonetheless, this more general solution leads one to a different interpretation of the results. In contrast to the aforementioned studies, the authors find that the equatorial thermocline is inherently more sensitive to local than to remote wind forcing and that planetary Rossby modes only weakly alter the spectral characteristics of the response. Tropical winds are able to generate a strong equatorial response with periods of 10 to 20 yr, while midlatitude winds can only do so for periods longer than about 50 yr. The results suggest that ocean basin modes are an unlikely explanation of decadal fluctuations in tropical Pacific sea surface temperature.
  • Physical Mechanisms Linking the Winter Pacific-North American Teleconnection Pattern to Spring ...Yan Ge, Gavin Gong, and Allan Frei | Journal of Climate, 2009 [+]
    Abstract: The wintertime Pacific–North American (PNA) teleconnection pattern has previously been shown to influence springtime snow conditions over portions of North America. This paper develops a more complete physical understanding of this linkage across the continent, using a recently released long-term, continentalscale gridded North American snow depth dataset and the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis data. An empirical orthogonal function–based filtering process is used to identify and isolate the interannual snow depth variations associated with PNA. Then linear and partial correlations are employed to investigate the physical mechanisms that link winter PNA with spring snow depth. In the positive phase of PNA, the enhanced PNA pressure centers lead to warmer temperatures over northwestern North America and less precipitation at midlatitudes. The temperature and precipitation pathways act independently and in distinct geographical regions, and together they serve to reduce winter snow depth across much of North America. Winter anomalies in the snow depth ?eld then tend to persist into spring. Dynamic mechanisms responsible for the PNA-influenced North American precipitation and temperature anomalies, involving moisture transport and cold air intrusions, are con?rmed in this study and also extended to continental snow depth anomalies.
  • Performance evaluation of elitist-mutated multi-objective particle swarm optimization for ...M. Janga Reddy and D. Nagesh Kumar | Journal of Hydroinformatics, 2009
  • Data mining for evolution of association rules for droughts and floods in India using climate inputsC. T. Dhanya and D. Nagesh Kumar | Journal of Geophysical Research, 2009 [+]
    Abstract: An accurate prediction of extreme rainfall events can significantly aid in policy making and also in designing an effective risk management system. Frequent occurrences of droughts and floods in the past have severely affected the Indian economy, which depends primarily on agriculture. Data mining is a powerful new technology which helps in extracting hidden predictive information (future trends and behaviors) from large databases and thus allowing decision makers to make proactive knowledge-driven decisions. In this study, a data-mining algorithm making use of the concepts of minimal occurrences with constraints and time lags is used to discover association rules between extreme rainfall events and climatic indices. The algorithm considers only the extreme events as the target episodes (consequents) by separating these from the normal episodes, which are quite frequent, and finds the time-lagged relationships with the climatic indices, which are treated as the antecedents. Association rules are generated for all the five homogenous regions of India and also for All India by making use of the data from 1960 to 1982. The analysis of the rules shows that strong relationships exist between the climatic indices chosen, i.e., Darwin sea level pressure, North Atlantic Oscillation, Nino 3.4 and sea surface temperature values, and the extreme rainfall events. Validation of the rules using data for the period 1983–2005 clearly shows that most of the rules are repeating, and for some rules, even if they are not exactly the same, the combinations of the indices mentioned in these rules are the same during validation period, with slight variations in the classes taken by the indices.
  • North American Temperature, Snowfall, and Snow Depth Response to Winter Climate ModesDebjani Ghatak, Gavin Gong, and Allan Frei | Journal of Climate, 2009 [+]
    Abstract: The snowpack is an important seasonal surface water storage reservoir that affects the availability of water resources during the spring and summer seasons in mid–high latitudes. Not surprisingly, interannual variations in snow cover extent and snow water equivalent have been extensively studied in arid regions such as western North America. This study broadens the focus by examining snow depth as an alternative snowpack metric, and considers its variability over different parts of North America. The authors use singular value decomposition (SVD) in conjunction with linear and partial correlation to show that regional snow-depth variations can be largely explained by the winter North Atlantic Oscillation (NAO) and the Pacific–North American (PNA) modes of atmospheric variability through distinct mechanistic pathways involving regional winter circulation patterns and hydrologic fluxes. The high index phase of the NAO generates positive winter air temperature anomalies over eastern parts of North America, causing thinning of the winter snowpack via snowmelt. Meanwhile, the high index phase of the PNA generates negative winter snowfall anomalies across midlatitudinal areas of North America, which also serve to thin the snowpack. Positive PNA anomalies have also been shown to increase temperatures and decrease snow depths over western North America. The PNA influence extends across the continent, whereas the NAO influence is limited to eastern North America. The winter snow-depth variations associated with all of these pathways exhibit seasonal persistence, which ultimately yield regional-scale spring snow-depth anomalies throughout much of North America.
  • Forecasting Spring Reservoir Inflows in Churchill Falls Basin in Québec, CanadaOli G. B. Sveinsson; Upmanu Lall; Vincent Fortin; Luc Perrault; Jocelyn Gaudet; Steve Zebiak | Journal of Hydrologic Engineering, 2008 [+]
    Abstract: The performance of different models and procedures for forecasting aggregated May–July streamflow for the Churchill Falls basin on the Québec-Labrador peninsula is compared. The models compared have different lead times and include an autoregressive model using only past streamflow data, an autoregressive with exogenous input model utilizing both past stream?ow and precipitation, and a linear regression model using the principal components of exogenous measures of atmospheric circulation inferred from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis project. The forecast skills of the different approaches are compared using a variety of measures of performance. The results indicate that relatively accurate forecasts using only measures of atmospheric circulation can be issued as early as in December of the prior year. A multimodel combination approach is found to be more effective than the use of a single forecast model. In addition, it is concluded that forecasting models utilizing atmospheric circulation data are useful, especially for basins where hydroclimatic observations are scarce and for basins where flows and other hydroclimatic variables are not strongly autocorrelated do not depend on their past.
  • Biokinetic Characterization of the Acceleration Phase in Autotrophic Ammonia OxidationKartik Chandran and Barth F. Smets | Water Environment Research, 2008 [+]
    Abstract: Batch autotrophic ammonia oxidation tracked through oxygen uptake measurements displays a preliminary acceleration phase. Failure to recognize the acceleration phase and fitting batch ammonia oxidation profiles with standard Monod-type mathematical models can result in meaningless kinetic parameter estimates. The objectives of this study were to examine the factors controlling the acceleration phase and to derive and test empirical and metabolic models for its description. Because of possible sustained reducing power limitation during batch ammonia oxidation, the extent of the acceleration phase (1) increased with increasing initial ammonia concentration, (2) did not systematically vary with initial biomass concentrations, and (3) increased in response to starvation. Concurrent hydroxylamine oxidation significantly reduced the acceleration phase potentially by relieving reducing power limitation. A nonlinear empirical model described the acceleration phase more accurately than a linear empirical model. The metabolic model also capture experimental trends exceedingly well, but required determination of additional parameters and variables.
  • Hierarchical Bayesian modeling of multisite daily rainfall occurrence: Rainy season onset, peak, endC. H. R. Lima and U. Lall | Water Resources Research, 2008 [+]
    Abstract: A quantitative definition of and ability to predict the onset and duration of the dominant rainfall season in a region are important for agricultural and natural resources management. In this paper, a methodology based on an analysis of daily rainfall occurrence is proposed and applied to define the onset and end of the rainfall season in northeast Brazil. Multiple rainfall gauges are considered simultaneously, and a hierarchical Bayesian framework is used for parameter estimation. The proposed model can be used to identify the rainy season onset by finding the first day of year in which the estimated probability of rainfall is greater than a specified number, e.g., 0.5. The determination of the end of the rainy season follows a similar procedure. Thus, the rainfall season can be defined as a period during which rainfall is most likely to occur. Monotonic trends are identified for the maximum probability of daily rainfall across the region, suggesting evidence of climate change. However, only the southern stations in the region exhibit a trend in the corresponding date. An examination of the correlations of dates of maximum rainfall probability with leading climate indicators leads to a promising direction for 1–3 month ahead forecasts of onset, which will be very useful for effective planning. Particularly, El Nin˜ o events in December are found to be associated with delays in the oncoming rainy season onset over a large part of southern northeast Brazil. Negative anomalies in the tropical South Atlantic sea surface temperature between January and March can anticipate the rainy season onset in the northern region and along the eastern coast of northeast Brazil.
  • Role of Retrospective Forecasts of GCMs Forced with Persisted SST Anomalies in Operational ...A. Sankarasubramanian, Upmanu Lall, and Susan Espinueva | Journal of Hydrometeorology, 2008 [+]
    Abstract: Seasonal streamflow forecasts contingent on climate information are essential for water resources planning and management as well as for setting up contingency measures during extreme years. In this study, operational streamflow forecasts are developed for a reservoir system in the Philippines using ECHAM4.5 precipitation forecasts (EPF) obtained using persisted sea surface temperature (SST) scenarios. Diagnostic analyses on SST conditions show that the tropical SSTs influence the streamflow during extreme years, whereas the local SSTs (0°–25°N, 115°–130°E) account for streamflow variability during normal years. Given that the EPF, local, and tropical SST conditions are spatially correlated, principal components regression (PCR) is employed to downscale the GCM-predicted precipitation fields and SST anomalies to monthly streamflow forecasts and to update them every month within the season using the updated EPF and SST conditions. These updated forecasts improve the prediction of monthly streamflows within the season in comparison to the skill of the monthly streamflow forecasts issued at the beginning of the season. It is also shown that the streamflow forecasting model developed using EPF under persisted SST conditions performs well upon employing EPF obtained under predicted SSTs as predictor. This has potential implications in the development of operational streamflow forecasts and statistical downscaling, which requires adequate years of retrospective GCM forecasts for recalibration. Finally, the study also shows that predicting the seasonal streamflow using the monthly precipitation forecasts reproduces the observed seasonal total better than the conventional approach of using seasonal precipitation forecasts to predict the seasonal streamflow.
  • Multimodel ensembles of streamflow forecasts: Role of predictor state in developing optimal ...Naresh Devineni, A. Sankarasubramanian, and Sujit Ghosh | Water Resources Research, 2008 [+]
    Abstract: A new approach for developing multimodel streamflow forecasts is presented. The methodology combines streamflow forecasts from individual models by evaluating their skill, represented by rank probability score (RPS), contingent on the predictor state. Using average RPS estimated over the chosen neighbors in the predictor state space, the methodology assigns higher weights for a model that has better predictability under similar predictor conditions. We assess the performance of the proposed algorithm by developing multimodel streamflow forecasts for Falls Lake Reservoir in Neuse River Basin, North Carolina (NC), through combining streamflow forecasts developed from two low-dimensional statistical models that use sea-surface temperature conditions as underlying predictors. To evaluate the proposed scheme thoroughly, we consider a total of seven multimodels that include existing multimodel combination techniques such as combining based on long-term predictability of individual models and by simple pooling of ensembles. Detailed nonparametric hypothesis tests comparing the performance of seven multimodels with two individual models show that the reduced RPS from multimodel forecasts developed based on the proposed algorithm is statistically significant from the RPSs of individual models and from the RPSs of existing multimodel techniques. The study also shows that adding climatological ensembles improves the multimodel performance resulting in reduced average RPS. Contingency analyses on categorical (tercile) forecasts show that the proposed multimodel combination technique reduces average Brier score and total number of false alarms, resulting in improved reliability of forecasts. However, adding multiple models with climatology also increases the number of missed targets (in comparison to individual models’ forecasts) which primarily results from the reduction of increased resolution that is exhibited in the individual models’ forecasts under various forecast probabilities.
  • Flushing History as a Hydrogeological Control on the Regional Distribution of Arsenic in Shallow ...A. van Geen, Y. Zheng, S. Goodbred, Jr., A. Horneman, Z. Aziz, Z. Cheng, M. Stute, B. Mailloux, ... | Environmental Science and Technology, 2008 [+]
    Abstract: Whereas serious health consequences of widespread consumption of groundwater elevated in As have been documented in several South Asian countries, the mechanisms responsible for As mobilization in reducing aquifers remain poorly understood. We document here a previously unrecognized and consistent relationship between dissolved As concentrations in reducing groundwater and the phosphate-mobilizable As content of aquifer sediment for a set of precisely depth-matched samples from across Bangladesh. The relationship holds across nearly 3 orders of magnitude in As concentrations and suggests that regional as well as local patterns of dissolved As in shallow groundwater are set by the solid phase according to a remarkably constant ratio of 250 µg/L dissolved As per 1 mg/kg P-mobilizable As. We use this relationship in a simple model of groundwater recharge to propose that the distribution of groundwater As in shallow aquifers of the Bengal Basin could primarily reflect the different flushing histories of sand formations deposited in the region over the past several thousand years.
  • Evolving strategies for crop planning and operation of irrigation reservoir system using ...M. Janga Reddy and D. Nagesh Kumar | Irrigation Science, 2008 [+]
    Abstract: In this paper multi-objective differential evolution (MODE) approach is proposed for the simultaneous evolution of optimal cropping pattern and operation policies for a multi-crop irrigation reservoir system. In general, farming community wants to maximize total net benefits by irrigating high economic value crops over larger area, which may also include water-intensive crops and longer duration crops. This poses a serious problem under waterscarce conditions and often results in crop failure. Under varying hydrological conditions, the fixed cropping pattern with conventional operating rule curve policies may not yield economically good results. To provide ?exible policies, a nonlinear multi-objective optimization model is formulated. To achieve robust performance by handling interdependent relationships among the decision variables of the model, the recent MODE technique is adopted to solve the multi-objective problem. The developed model is applied for ten-daily reservoir operation to a case study in India. The model results suggest that changes in the hydrologic conditions over a season have considerable impact on the cropping pattern and net benefits from the irrigation system. Towards this purpose, the proposed MODE model can be used to evolve different strategies for irrigation planning and reservoir operation policies, and to select the best possible solution appropriate to the forecasted hydrologic condition.
  • Would Advance Knowledge of 1930s SSTs Have Allowed Prediction of the Dust Bowl Drought?Richard Seager, Yochanan Kushnir, Mingfang Ting, Mark Cane, Naomi Naik and Jennifer Miller | Journal of Climate, 2008 [+]
    Abstract: Could the Dust Bowl drought of the 1930s have been predicted in advance if the SST anomalies of the 1930s had been foreknown? Ensembles of model simulations forced with historical observed SSTs in the global ocean, and also separately in the tropical Pacific and Atlantic Oceans, are compared with an ensemble begun in January 1929 with modeled atmosphere and land initial conditions and integrated through the 1930s with climatological SSTs. The ensemble with climatological SSTs produces values for the precipitation averaged over 1932–39 that are not statistically different from model climatology. In contrast, the ensembles with global SST forcing produce a drought centered in the central plains and southwestern North America that is clearly separated from the model climatology. Both the tropical Pacific and northern tropical Atlantic SST anomalies produce a statistically significant model drought in this region. The modeled drought has a spatial pattern that is different from the observed drought, which was instead centered in the central and northern plains and also impacted the northern Rocky Mountain states but not northeastern Mexico. The model error in extending the Dust Bowl drought too far south is attributed to an incorrect response of the model to warm subtropical North Atlantic SST anomalies. The model error in the northern states cannot be attributed to an incorrect response to tropical SST anomalies. The model also fails to reproduce the strong surface air warming across most of the continent during the 1930s. In contrast, the modeled patterns of precipitation reduction and surface air temperature warming during the 1950s drought are more realistic. Tree-ring records show that the Dust Bowl pattern of drought has occurred before, suggesting that while the extensive human-induced land surface degradation and dust aerosol loading of the 1930s drought may have played an important role in generating the observed drought pattern, natural processes, possibly including land interactions, are capable of generating droughts centered to the north of the main ENSO teleconnection region. Despite this caveat, advance knowledge of tropical SSTs alone would have allowed a high-confidence prediction of a multiyear and severe drought, but one centered too far south and without strong cross-continental warming.
  • Predictability of Sri Lankan rainfall based on ENSOLareef Zubair, Manjula Siriwardhan, Janaki Chandimala and Zeenas Yahiya | International Journal of Climatology, 2008 [+]
    Abstract: Investigating the year-round rainfall of Sri Lanka provides understanding into the South Asian monsoon system as it compliments studies on the Indian summer monsoon. The El Nino-Southern Oscillation (ENSO) is a primary ˜ mode of climate variability of this area. Here, the predictability of Sri Lanka rainfall based on ENSO is quantified based on composite analysis, correlations and contingency tables. The rainfall is modestly predictable based on ENSO during January–March, July–August and October –December. El Nino typically leads to wetter conditions during October to ˜ December and drier conditions during January to March and July to August on average. The correlations of ENSO indices with rainfall are statistically signi?cant for October to December, January to March and July to August and an analysis based on contingency tables shows modest predictability. The use of ENSO indices derived from the central Pacific sea surfaces improves the predictability from January to June. The predictability in the mountain regions is diminished when garnering orographic rainfall. The predictability in the east is diminished during the cyclone season. The predictability based on ENSO for October to December rainfall is robust on a decadal scale while the predictability of January to March and July to August rainfall has acquired significance in recent decades. An ENSO-based scheme that is adapted to each season and region, and takes account of decadal variations can thus provide skillful rainfall predictions.
  • Warming Trend of the Indian Ocean SST and Indian Ocean Dipole from 1880 to 2004Chie Ihara, Yochanan Kushnir, and Mark A. Cane | Journal of Climate, 2008 [+]
    Abstract: The state of the Indian Ocean dipole representing the SST anomaly difference between the western and southeastern regions of the ocean is investigated using historical SST reconstructions from 1880 to 2004. First, the western and eastern poles of the SST-based dipole mode index are analyzed separately. Both the western and eastern poles display warming trends over this period, particularly after the 1950s. The western pole tends to be anomalously colder than the eastern pole from 1880 to 1919, whereas in the interval 1950–2004 the SST anomalies over the western pole are comparable to those over the eastern pole though there are occasional outliers where the eastern pole is anomalously colder than the western pole. The tendencies of the occurrences of positive and negative dipole events in September–November show three distinct regimes during the period analyzed. In 1880–1919, negative dipole events associated with La Niña events occur more frequently than positive events. In 1920–49, some weak positive events occur relatively independently of El Niño events over the Pacific. The period of 1960–2004 is characterized by strong and frequent occurrences of positive events associated with El Niño events.
  • Hydroclimatic risk to economic growth in Sub-Saharan AfricaCasey Brown, Robyn Meeks, Kenneth Hunu, and Winston Yu | The International Research Institute for Climate and Society, 2008 [+]
    Abstract: In order to plan strategies for adaptation to climate change, the current effects of climate on economic growth needs to be understood. This study reviews evidence of climate effects on economic growth and presents original analysis of the effect in Sub-Saharan Africa (SSA). Case studies from the literature demonstrate that historically, climate has had significant and negative effects on household income, agricultural productivity and economic growth in SSA. This study focuses on the effects hydroclimatic variability on economic growth in the countries of SSA. We utilize a new national level precipitation statistic that incorporates spatial and temporal variability within each country. Country level economic growth statistics are analyzed with cross-country and panel regressions. Persistent negative precipitation anomalies (drought) are found to be the most significant climate influence on economic growth. This result is consistent across all model specifications and across several measures of welfare and economic activity. Temperature and precipitation variability show significant effects in some cases. Results imply the consideration of hydroclimatic risks, namely drought, may be the priority concern for adaptation to a changing climate for Sub-Saharan Africa. This conclusion is contrary to the focus of many climate change impact assessments that focus on temperature increases as the primary concern.
  • Inclusão de Informação Climática e Variabilidade Espacial Em Modelos Estatíscos de Previsão de ...Carlos Henrique Ribeiro Lima and Upmanu Lall | II Simpósio de Recursos Hídricos do Sul-Sudeste, 2008
  • Non-parametric short-term forecasts of the Great Salt Lake using atmospheric indicesYoung-Il Moon, Upmanu Lall and Hyun-Han Kwon | International Journal of Climatology, 2008 [+]
    Abstract: A multivariate, non-parametric model for approximating the non-linear dynamics of hydroclimatic variables is developed and applied for forecasting the volume of the Great Salt Lake (GSL) of Utah. The monthly volume of the GSL is presumed to depend on recent volumes of the lake, and on three atmospheric circulation indices. The indices considered are the Southern oscillation index (SOI), the pacific/North America (PNA) climatic index, and the central North Pacific (CNP) climatic index. Locally weighted polynomials with automatically and locally chosen parameters are used for developing a non-linear forecasting model. Estimated average mutual information (M.I) is used to select appropriate lags across each time series. Iterated and direct multi-step predictions of lake volumes for up to 2 years in the future with and without the atmospheric indices are compared. The atmospheric circulation information can lead to significant improvements in the predictability of the lake.
  • Basin-scale stream-flow forecasting using the information of large-scale atmospheric circulation ...Rajib Maity and D. Nagesh Kumar | Hydrological Processes, 2008 [+]
    Abstract: It is well recognized that the time series of hydrologic variables, such as rainfall and stream?ow are significantly influenced by various large-scale atmospheric circulation patterns. The influence of El Nino-southern oscillation (ENSO) on hydrologic ˜ variables, through hydroclimatic teleconnection, is recognized throughout the world. Indian summer monsoon rainfall (ISMR) has been proved to be significantly influenced by ENSO. Recently, it was established that the relationship between ISMR and ENSO is modulated by the influence of atmospheric circulation patterns over the Indian Ocean region. The influences of Indian Ocean dipole (IOD) mode and equatorial Indian Ocean oscillation (EQUINOO) on ISMR have been established in recent research. Thus, for the Indian subcontinent, hydrologic time series are significantly influenced by ENSO along with EQUINOO. Though the influence of these large-scale atmospheric circulations on large-scale rainfall patterns was investigated, their influence on basin-scale stream-flow is yet to be investigated. In this paper, information of ENSO from the tropical Pacific Ocean and EQUINOO from the tropical Indian Ocean is used in terms of their corresponding indices for stream-flow forecasting of the Mahanadi River in the state of Orissa, India. To model the complex non-linear relationship between basinscale stream-flow and such large-scale atmospheric circulation information, artificial neural network (ANN) methodology has been opted for the present study. Efficient optimization of ANN architecture is obtained by using an evolutionary optimizer based on a genetic algorithm. This study proves that use of such large-scale atmospheric circulation information potentially improves the performance of monthly basin-scale stream-flow prediction which, in turn, helps in better management of water resources.
  • July droughts Homogenous Indian Monsoon region and Indian Ocean dipole during El Niño eventsChie Ihara, Yochanan Kushnir, and Mark A. Cane | International Journal of Climatology, 2008 [+]
    Abstract: The monthly summer monsoon rainfall over the Homogeneous Indian Monsoon region (HI) that represents most of the variance of all-India monsoon rainfall is investigated using observational data from 1880 to 2002. Severe droughts in July occur mostly during El Nino events of the boreal summer monsoon season. They occurred frequently in the late 19th to early 20th century, rarely in the middle of the 20th century, and again occasionally occurred after the 1960s. During El Nino events, severe droughts in July over HI are significantly associated with smaller sea surface temperature- (SST) based Indian Ocean Dipole mode index (SSTDMI) in May and July compared to the years without these outstanding events. The evolution of SSTDMI that usually starts around May/June during El Nino events tends to delay when July precipitation over HI is abnormally low. Nino3 values from May through October are not signi?cantly associated with severe droughts over HI in July during El Nino events indicating that the strength of El Ni ˜ no events is not related to the occurrences of severe droughts in July.
  • Water in the 21st Century: Defining the Elements of Global Crises and Potential SolutionsLall, U. T. Heikkila, C. Brown and T. Siegfried | Journal of International Affairs , 2008 [+]
    Abstract: Will we run out of fresh water in the 21 st century? The media highlights the parched lands, dry riverbeds and springs and falling groundwater tables across the world daily. Over a billion people living in developing countries without access to safe drinking water are facing economic and water poverty' I Another real and troubling indicator is the rapid rate of aquatic habitat degradation and biodiversity loss in the last century. Projected changes in climate due to greenhouse gases invariably portray a future world that is much drier in the tropics-where over half the world's population lives-and suggest a global increase in floods and droughts. Is a global water crisis already upon us? The answer to this question seems to depend on who you ask. On the one hand, active voices such as Sandra Postel, Peter Gleick, Vandana Shiva, Lester Brown and Paul Elrich, as well as leaders of major global organizations with an interest in water, have been warning of an impending global water catastrophe. On the other hand, the mainstream academic community involved in hydrology and water has largely ignored the topic. For example, a Google search for "water crisis" leads to almost 1 million hits, but the same search on Google Scholar yields approximately 4,000 hits as compared to over 1 million Google Scholar hits for "climate change." Many of these articles focus on policy solutions, but do not necessarily explore the nature of the problem in-depth. Furthermore, the literature is largely non-American and contains references to much of the same work. Introducing "global water crisis" into a Google search reduces the number of hits by a factor of ten. In fact, the handful of scientists who do study this problem have divergent opinions as to whether and when the world will run out of water. A handful of scholars-particularly economists-go so far as to claim that a global water crisis does not exist or is, at best, overstated. These scholars generally find that, on the whole, water access is improving worldwide and that with continued efficiency enhancements, the amount of water will continue to meet existing demands. Perhaps the way the global water crisis has been defined-whether the world will run out of freshwater-is the wrong way to look at the problem. While there are many scholars looking at the range of localized and specific water challenges that are occurring around the globe, it seems that the academic community has yet to find success in accurately characterizing the sum of their parts. In this article, we argue that there are three distinct water crises-or challenges, depending on who you ask, that have yet to be systematically connected by scholars. It is by looking at how these three challenges are interrelated that we can better articulate the global characteristics of water resource dilemmas and, ultimately, identify the global factors that can help solve these dilemmas.
  • Multivariate streamflow forecasting using independent component analysisSeth Westra, Ashish Sharma, Casey Brown, and Upmanu Lall | Water Resources Research, 2008 [+]
    Abstract: Seasonal forecasting of streamflow provides many benefits to society, by improving our ability to plan and adapt to changing water supplies. A common approach to developing these forecasts is to use statistical methods that link a set of predictors representing climate state as it relates to historical streamflow, and then using this model to project streamflow one or more seasons in advance based on current or a projected climate state. We present an approach for forecasting multivariate time series using independent component analysis (ICA) to transform the multivariate data to a set of univariate time series that are mutually independent, thereby allowing for the much broader class of univariate models to provide seasonal forecasts for each transformed series. Uncertainty is incorporated by bootstrapping the error component of each univariate model so that the probability distribution of the errors is maintained. Although all analyses are performed on univariate time series, the spatial dependence of the streamflow is captured by applying the inverse ICA transform to the predicted univariate series. We demonstrate the technique on a multivariate streamflow data set in Colombia, South America, by comparing the results to a range of other commonly used forecasting methods. The results show that the ICA-based technique is significantly better at representing spatial dependence, while not resulting in any loss of ability in capturing temporal dependence. As such, the ICA-based technique would be expected to yield considerable advantages when used in a probabilistic setting to manage large reservoir systems with multiple inflows or data collection points.
  • Epochal changes in the association between malaria epidemics and El Niño in Sri LankaL. Zubair, G. N. Galappaththy, H. Yang, J. Chandimala, Z. Yahiya, P. Amerasinghe, N. Ward, and ... | Malaria Journal, 2008 [+]
    Abstract: Background: El Niño events were suggested as a potential predictor for malaria epidemics in Sri Lanka based on the coincidence of nine out of 16 epidemics with El Niño events from 1870 to 1945. Here the potential for the use of El Niño predictions to anticipate epidemics was examined using enhanced climatic and epidemiological data from 1870 to 2000. Methods: The epidemics start years were identified by the National Malaria Control Programme and verified against epidemiological records for consistency. Monthly average rainfall climatologies were estimated for epidemic and non-epidemic years; as well El Niño, Neutral and La Niña climatic phases. The relationship between El Niño indices and epidemics was examined to identify 'epochs' of consistent association. The statistical significance of the association between El Niño and epidemics for different epochs was characterized. The changes in the rainfall-El Niño relationships over the decade were examined using running windowed correlations. The anomalies in rainfall climatology during El Niño events for different epochs were compared. Results: The relationship between El Niño and epidemics from 1870 to 1927 was confirmed. The anomalies in monthly average rainfall during El Niño events resembled the anomalies in monthly average rainfall during epidemics during this period. However, the relationship between El Niño and epidemics broke down from 1928 to 1980. Of the three epidemics in these six decades, only one coincided with an El Niño. Not only did this relationship breakdown but epidemics were more likely to occur in periods with a La Niña tendency. After 1980, three of four epidemics coincided with El Niño. Conclusion: The breakdown of the association between El Niño and epidemics after 1928 is likely due to an epochal change in the El Niño-rainfall relationship in Sri Lanka around the 1930's. It is unlikely that this breakdown is due to the insecticide spraying programme that began in 1945 since the breakdown started in 1928. Nor does it explain the occurrence of epidemics during La Niña phase from 1928 to 1980. Although there has been renewed coincidence with El Niño after 1980, this record is too short for establishing a reliable relationship.
  • Review of Downscaling Methodologies for Africa Climate ApplicationsCasey Brown, Arthur Greene, Paul Block, and Alessandra Giannini | The International Research Institute for Climate and Society, 2008 [+]
    Abstract: Downscaling is the term used to describe the various methods used to translate the climate projections from coarse resolution GCMs to finer resolutions deemed more useful for assessing impacts. Projections of future climate are produced using complex, coupled atmosphere-ocean models (GCMs). The GCMs are most reliable at the continental scale. Due to the inherent uncertainty of the climate system and the inevitable existence of model errors, multi-model ensembling is the recommended approach for characterizing expected climate changes. As downscaling is dependent on the ability of GCMs to successfully project the climate change signal, it is limited to where that signal is clear. Assessments of climate change in Africa indicate some consensus of reduced winter rainfall in southern Africa, increased annual rainfall in east Africa and uncertainty for the rest of Africa. Selection of GCMs that “do better” over Africa, or any region, is difficult and probably not warranted, given the general parity in model skill and the difficulty in identifying which models are more skillful. Ensemble means or medians offer the highest level of projection accuracy. Downscaling approaches are generally categorized as dynamical, using regional climate models, and statistical, using empirical relationships. However, dynamical downscaling often includes statistical modeling in the form of “bias correction.” Dynamical downscaling is useful for incorporating topographic features, such as strong orography, and land use and vegetation. It is recommended where those features play a significant role in regional climate. However, computational time and the uncertainties that accompany complex models outweigh the benefits of dynamical downscaling where these features are not significant. The spatial resolution that can be achieved is on the order of tens of kilometers. Statistical downscaling is simpler and more efficient than dynamical downscaling. It is preferred where estimates of specific variables, especially at point locations, are sought for input to sector models (e.g., hydrologic models) or decision making. However, statistical modeling can mask a true understanding of regional climate dynamics and estimates may be overconfident. In summary, downscaling is best understood as an attempt to increase the understanding of climate change influences at the regional scale. In that context, a variety of methodologies should be explored, using all tools possible to increase that understanding. A set of “Best Practices” is recommended for pursuing this effort.
  • Observed Inconsistencies between Snow Extent and Snow Depth Variability at Regional/Continental ...Yan Ge and Gavin Gong | Journal of Climate, 2008 [+]
    Abstract: Snow extent and snow depth are two related characteristics of a snowpack, but they do not need to be mutually consistent. Differences between these two variables at local scales are readily apparent. However, at larger scales, which interact with atmospheric circulation and climate, snow extent is the primary variable considered, owing largely to the scarcity of snow depth data. In this study, three regional-/continental-scale gridded snow depth/snow water equivalent (SWE) datasets, derived from station observations or passive microwave satellite sensors, are utilized to quantitatively evaluate the relationship between snow extent and snow depth/SWE over North America. Various statistical methods are used to ensure the robustness of the results, including correlations, composites, and singular value decomposition analyses. Results indicate that continental-scale snow depth variations are substantial in their own right and that depth and extent anomalies are largely unrelated over broad high-latitude regions north of the snow line. Snow extent and snow depth vary more consistently in the vicinity of the snow line, especially in autumn and spring, during which precipitation and ablation can affect both variables. It is also found that deeper (shallower) winter snow translates into larger (smaller) snow-covered areas in the following spring/summer season, and also a longer (shorter) snow season, but only in specific regions. These results suggest a possible influence of snow depth on spring and summer climate. Overall, the observed lack of mutual consistency between these two snowpack variables at continental/regional scales suggests that snow depth variations may be of sufficiently large magnitude, spatial scope, and temporal duration to interact with regional– hemispheric climate, in a manner unrelated to the more extensively studied snow extent variations.
  • Volcanoes and ENSO over the Past MillenniumJulien Emile-Geay, Richard Seager, Mark A. Cane, Edward R. Cook, and Gerald H. Haug | Journal of Climate, 2008 [+]
    Abstract: The controversial claim that El Niño events might be partially caused by radiative forcing due to volcanic aerosols is reassessed. Building on the work of Mann et al., estimates of volcanic forcing over the past millennium and a climate model of intermediate complexity are used to draw a diagram of El Niño likelihood as a function of the intensity of volcanic forcing. It is shown that in the context of this model, only eruptions larger than that of Mt. Pinatubo (1991, peak dimming of about 3.7 W m2 ) can shift the likelihood and amplitude of an El Niño event above the level of the model’s internal variability. Explosive volcanism cannot be said to trigger El Niño events per se, but it is found to raise their likelihood by 50% on average, also favoring higher amplitudes. This reconciles, on one hand, the demonstration by Adams et al. of a statistical relationship between explosive volcanism and El Niño and, on the other hand, the ability to predict El Niño events of the last 148 yr without knowledge of volcanic forcing. The authors then focus on the strongest eruption of the millennium (A.D. 1258), and show that it is likely to have favored the occurrence of a moderate-to-strong El Niño event in the midst of prevailing La Niña–like conditions induced by increased solar activity during the well-documented Medieval Climate Anomaly. Compiling paleoclimate data from a wide array of sources, a number of important hydroclimatic consequences for neighboring areas is documented. The authors propose, in particular, that the event briefly interrupted a solar-induced megadrought in the southwestern United States. Most of the time, however, volcanic eruptions are found to be too small to significantly affect ENSO statistics.
  • Bayesian dynamic modeling for nonstationary hydroclimatic time series forecasting along with ...D. Nagesh Kumar and Rajib Maity | Hydrological Processes, 2008 [+]
    Abstract: Forecasting of hydrologic time series, with the quantification of uncertainty, is an important tool for adaptive water resources management. Nonstationarity, caused by climate forcing and other factors, such as change in physical properties of catchment (urbanization, vegetation change, etc.), makes the forecasting task too difficult to model by traditional Box–Jenkins approaches. In this paper, the potential of the Bayesian dynamic modelling approach is investigated through an application to forecast a nonstationary hydroclimatic time series using relevant climate index information. The target is the time series of the volume of Devil’s Lake, located in North Dakota, USA, for which it was proved difficult to forecast and quantify the associated uncertainty by traditional methods. Two different Bayesian dynamic modelling approaches are discussed, namely, a constant model and a dynamic regression model (DRM). The constant model uses the information of past observed values of the same time series, whereas the DRM utilizes the information from a causal time series as an exogenous input. Noting that the North Atlantic Oscillation (NAO) index appears to co-vary with the time series of Devil’s Lake annual volume, its use as an exogenous predictor is explored in the case study. The results of both the Bayesian dynamic models are compared with those from the traditional Box–Jenkins time series modelling approach. Although, in this particular case study, it is observed that the DRM performs marginally better than traditional models, the major strength of Bayesian dynamic models lies in the quantification of prediction uncertainty, which is of great value in hydrology, particularly under the recent climate change scenario.
  • Degradation rates of CFC-11, CFC-12 and CFC-113 in anoxic shallow aquifers of Araihazar, BangladeshA. Horneman, M. Stute, P. Schlosser, W. Smethie Jr., N. Santella, D.T. Ho, B. Mailloux, ... | Journal of Contaminant Hydrology, 2008 [+]
    Abstract: Chlorofluorocarbons CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CCl2F–CClF2) are used in hydrology as transient tracers under the assumption of conservative behavior in the unsaturated and saturated soil zones. However, laboratory and field studies have shown that these compounds are not stable under anaerobic conditions. To determine the degradation rates of CFCs in a tropical environment, atmospheric air, unsaturated zone soil gas, and anoxic groundwater samples were collected in Araihazar upazila, Bangladesh. Observed CFC concentrations in both soil gas and groundwater were significantly below those expected from atmospheric levels. The CFC deficits in the unsaturated zone can be explained by gas exchange with groundwater undersaturated in CFCs. The CFC deficits observed in 3 H/ 3 He dated groundwater were used to estimate degradation rates in the saturated zone. The results show that CFCs are degraded to the point where practically no (b5%) CFC-11, CFC-12, or CFC-113 remains in groundwater with 3 H/ 3 He ages above 10 yr. In groundwater sampled at our site CFC-11 and CFC-12 appear to degrade at similar rates with estimated degradation rates ranging from ~0.25 yr ?1 to ~6 yr ?1 . Degradation rates increased as a function of reducing conditions. This indicates that CFC dating of groundwater in regions of humid tropical climate has to be carried out with great caution.
  • The Influence of Cloud and Surface Properties on the Arctic Ocean Shortwave Radiation Budget in ...Irina V. Gorodetskaya, L.-Bruno Tremblay, Beate Liepert, Mark A. Cane, and Richard I. Cullather | Journal of Climate, 2008 [+]
    Abstract: The impact of Arctic sea ice concentrations, surface albedo, cloud fraction, and cloud ice and liquid water paths on the surface shortwave (SW) radiation budget is analyzed in the twentieth-century simulations of three coupled models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report. The models are the Goddard Institute for Space Studies Model E-R (GISS-ER), the Met Office Third Hadley Centre Coupled Ocean–Atmosphere GCM (UKMO HadCM3), and the National Center for Atmosphere Research Community Climate System Model, version 3 (NCAR CCSM3). In agreement with observations, the models all have high Arctic mean cloud fractions in summer; however, large differences are found in the cloud ice and liquid water contents. The simulated Arctic clouds of CCSM3 have the highest liquid water content, greatly exceeding the values observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) campaign. Both GISS-ER and HadCM3 lack liquid water and have excessive ice amounts in Arctic clouds compared to SHEBA observations. In CCSM3, the high surface albedo and strong cloud SW radiative forcing both significantly decrease the amount of SW radiation absorbed by the Arctic Ocean surface during the summer. In the GISS-ER and HadCM3 models, the surface and cloud effects compensate one another: GISS-ER has both a higher summer surface albedo and a larger surface incoming SW flux when compared to HadCM3. Because of the differences in the models’ cloud and surface properties, the Arctic Ocean surface gains about 20% and 40% more solar energy during the melt period in the GISS-ER and HadCM3 models, respectively, compared to CCSM3. In twenty-first-century climate runs, discrepancies in the surface net SW flux partly explain the range in the models’ sea ice area changes. Substantial decrease in sea ice area simulated during the twenty-first century in CCSM3 is associated with a large drop in surface albedo that is only partly compensated by increased cloud SW forcing. In this model, an initially high cloud liquid water content reduces the effect of the increase in cloud fraction and cloud liquid water on the cloud optical thickness, limiting the ability of clouds to compensate for the large surface albedo decrease. In HadCM3 and GISS-ER, the compensation of the surface albedo and cloud SW forcing results in negligible changes in the net SW flux and is one of the factors explaining moderate future sea ice area trends. Thus, model representations of cloud properties for today’s climate determine the ability of clouds to compensate for the effect of surface albedo decrease on the future shortwave radiative budget of the Arctic Ocean and, as a consequence, the sea ice mass balance.
  • Timing of El Niño-Related Warming And Indian Summer Monsoon RainfallChie Ihara, Yochanan Kushnir, Mark A. Cane, and Alexey Kaplan | Journal of Climate, 2008 [+]
    Abstract: The relationship between all-India summer monsoon rainfall (ISMR) and the timing of (El Niño– Southern Oscillation) ENSO-related warming/cooling is investigated, using observational data during the period from 1881 to 1998. The analysis of the evolutions of Indo-Pacific sea surface temperature (SST) anomalies suggests that when ISMR is not below normal despite the co-occurrence of an El Niño event, warming over the eastern equatorial Pacific starts from boreal winter and evolves early so that the westerncentral Pacific and Indian Ocean are warmer than normal during the summer monsoon season. In contrast, when the more usual El Niño–dry ISMR relationship holds, the eastern equatorial Pacific starts warming rapidly only about a season before the reference summer so that the western-central Pacific and Indian Oceans remain cold during the monsoon season.
  • Distinctive Microbial Ecology and Biokinetics of Autotrophic Ammonia and Nitrite Oxidation in a ...Joon Ho Ahn, Ran Yu, Kartik Chandran | Biotechnology and Bioengineering, 2008 [+]
    Abstract: Biological nitrogen removal (BNR) based on partial nitrification and denitrification via nitrite is a cost-effective alternate to conventional nitrification and denitrification (via nitrate). The goal of this study was to investigate the microbial ecology, biokinetics, and stability of partial nitrification. Stable long-term partial nitrification resulting in 82.1 +/- 17.2% ammonia oxidation, primarily to nitrite (77.3 +/- 19.5% of the ammonia oxidized) was achieved in a lab-scale bioreactor by operation at a pH, dissolved oxygen and solids retention time of 7.5 +/- 0.1, 1.54 +/- 0.87 mg O2 /L, and 3.0 days, respectively. Bioreactor ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) populations were most closely related to Nitrosomonas europaea and Nitrobacter spp., respectively. The AOB population fraction varied in the range 61+/-  45% and was much higher than the NOB fraction, 0.71 +/- 1.1%. Using direct measures of bacterial concentrations in conjunction with independent activity measures and mass balances, the maximum specific growth rate (mmax), specific decay (b) and observed biomass yield coefficients (Yobs) for AOB were 1.08 +/- 1.03 day^-1, 0.32 +/- 0.34 day^-1, and 0.15 +/- 0.06 mg biomass COD/mg N oxidized, respectively. Corresponding mmax, b, and Yobs values for NOB were 2.6 +/- 2.05 day^-1, 1.7 +/- 1.9 day^-1, and 0.04 +/- 0.02 mg biomass COD/mg N oxidized, respectively. The results of this study demonstrate that the highly selective partial nitrification operating conditions enriched for a narrow diversity of rapidly growing AOB and NOB populations unlike conventional BNR reactors, which host a broader diversity of nitrifying bacteria. Further, direct measures of microbial abundance enabled not only elucidation of mixed community microbial ecology but also estimation of key engineering parameters describing bioreactor systems supporting these communities.
  • Dust and sea surface temperature forcing of the 1930sBenjamin I. Cook, Ron L. Miller, and Richard Seager | Geophysical Research Letters, 2008 [+]
    Abstract: Droughts over the central United States (US) are modulated by sea surface temperature (SST) variations in the eastern tropical Pacific. Many models, however, are unable to reproduce the severity and spatial pattern of the ‘‘Dust Bowl’’ drought of the 1930s with SST forcing alone. We force an atmosphere general circulation model with 1930s SSTs and model-generated dust emission from the Great Plains region. The SSTs alone force a drought over the US similar to observations, but with a weaker precipitation anomaly that is centered too far south. Inclusion of dust radiative forcing, centered over the area of observed wind erosion, increases the intensity of the drought and shifts its center northward. While our conclusions are tempered by limited quantitative observations of the dust aerosol load and soil erosion during this period, our study suggests that unprecedented atmospheric dust loading over the continental US exacerbated the ‘‘Dust Bowl’’ drought.
  • Tropical Pacific Forcing of North American Medieval Megadroughts: Testing the Concept with an ...R. Seager, R. Burgman, Y. Kushnir, A. Clement, E. Cook, N. Naik, and J. Miller | Journal of Climate, 2008 [+]
    Abstract: The possible role that tropical Pacific SSTs played in driving the megadroughts over North America during the medieval period is addressed. Fossil coral records from the Palmyra Atoll are used to derive tropical Pacific SSTs for the period from A.D. 1320 to A.D. 1462 and show overall colder conditions as well as extended multidecadal La Niña–like states. The reconstructed SSTs are used to force a 16-member ensemble of atmosphere GCM simulations, each with different initial conditions, with the atmosphere coupled to a mixed layer ocean outside of the tropical Pacific. Model results are verified against North American tree ring reconstructions of the Palmer Drought Severity Index. A singular value decomposition analysis is performed using the soil moisture anomaly simulated by another 16-member ensemble of simulations forced by global observed SSTs for 1856–2004 and tree ring reconstructions of the Palmer Drought Severity Index for the same period. This relationship is used to transfer the modeled medieval soil moisture anomaly (relative to the modern simulation) into a model-estimated Palmer Drought Severity Index. The model-estimated Palmer Drought Severity Index reproduces many aspects of both the interannual and decadal variations of the tree ring reconstructions, in addition to an overall drier climate that is drier than the tree ring records suggest. The model-estimated Palmer Drought Severity Index simulates two previously identified “megadroughts,” A.D. 1360–1400 and A.D. 1430–60, with a realistic spatial pattern and amplitude. In contrast, the model fails to produce a period of more normal conditions in the early fifteenth century that separated these two megadroughts. The dynamical link between tropical SSTs and the North American megadroughts is akin to that operating in modern droughts. The model results are used to argue that the tropical Pacific played an active role in driving the megadroughts. However, the match between simulated and reconstructed hydroclimate is such that it is likely that both the coral-reconstructed SST anomalies contain significant errors and that SST anomalies in other basins also played a role in driving hydroclimate variations over North America during the late medieval period.
  • The global footprint of persistent extra-tropical drought in the instrumental eraCeline Herweijer and Richard Seager | International Journal of Climatology , 2008 [+]
    Abstract: The major North American droughts as per instrumental records are shown to be part of a larger, global pattern of low-frequency drought variability. Drought in western North America during the 1850s–1860s, 1870s, 1890s, 1930s and 1950s, is shown to coincide with the occurrence of prolonged dry spells in parts of Europe, southern South America and western Australia. Tropical land regions are mostly wet during these periods, with the exception of central east Africa, southern India and Sri Lanka, which are dry. The recent 1998–2003 period of drought in western North America reveals a similar global hydroclimatic ‘footprint’ with the exception of a wet southern South America and continued dry conditions in the Sahel. Common to each of the six droughts is the persistence of anomalously cool east central tropical Pacific sea surface temperatures (SSTs). For the 1998–2003 case, the warming of SSTs everywhere outside of the east central tropical Pacific may be influencing precipitation and masking the influence of persistent precipitation anomalies driven from the tropical Pacific alone. In general, examination of these major historical extra-tropical droughts reveals a hemispherically and, in the extra-tropics, a zonally symmetric pattern consistent with forcing from the Tropics. Ensembles of model simulations forced by observed SSTs globally (Global Ocean Global Atmosphere, GOGA) and only within the tropical Pacific (Pacific Ocean Global Atmosphere-Mixed Layer, POGA-ML) are both able to capture the global pattern of the persistent extra-tropical drought regimes since the mid-nineteenth century. This implies that the recently demonstrated link between SST forcing and drought in North America is in fact only one part of a global hydroclimatic response to the persistence of cool SST anomalies in the tropical Pacific. Indian Ocean SST forcing is required to capture the droughts in central east Africa. Over Europe, the modelled, low-frequency precipitation signal is unrealistically ENSO dominated, as the model does not faithfully reproduce the observed history of low-frequency NAO variability. Overall, our results suggest that the global pattern of persistent drought appears to be a low-frequency version of interannual ENSO-forced variability.
  • The Interlinking of Indian Rivers: Questions on the Scientific, Economic and Environmental ...Jayanta Bandyopadhyay and Shama Perveen | Interlinking of Rivers in India: Issues and Concerns, 2008 [+]
    Abstract: The availability of freshwater at various spots on the Earth’s terrestrial surface will continue to be determined by the hydrological cycle, till such a time when technologies like desalination of seawater is practiced on a reasonably extended scale. The rapid growth in the demand of freshwater driven by growth in the global population and of the economies, has led to this natural resource becoming scarce in many parts of the world. As a result, the ratio between the number of people and the available water resource is worsening day by day. By 2020, the global population is projected to be in the range of 7.3 to 7.9 billion, which is 50 per cent larger than that in 1990 (UN, 2006). Because of this rapidly growing human population, the world may see more than a six-fold increase in the number of people living in conditions of water stress - from 470 million today to 3 billion in 2025 (Postel, 1999). In the global picture, India is identified as a country where water scarcity is expected to grow considerably in the coming decades. Further, drought conditions resulting from climatic variability cause considerable human suffering in many parts of the country, in the form of scarcity of water for both satisfaction of domestic needs and for crop protection. The project for interlinking of rivers of India emanates from a desire of the political leadership of the country to bring a permanent solution to the negative impacts of drought and water shortages in these parts (IWRS, 1996). Such a desire is, without question, worthy of applause because satisfaction of domestic water needs should be considered as a human right and be given the top priority.
  • Thirsty for Change: Considering Water Privatization in Developing NationsJ. R. Foshee, A. Ghosh, C. Graham, W. Murray, C. Ruben-Salama, and T. Siegfried | Consilience: The Journal of Sustainable Development, 2008 [+]
    Abstract: Access, maintenance, and distribution of clean water are daunting tasks for developing nations. Efforts to provide clean drinking water have often fallen short, which has prompted the World Bank to advocate for privatization. From a theoretical perspective, privatization blends the advantages of corporate efficiency with responsible management on behalf of the national government. Analysis of attempts to privatize water in the Philippines, with the establishment of the Metropolitan Waterworks Sewerage System (MWSS), shows mixed results. Between 1997 and 2003, citizens with access to water increased from 58 percent to 84 percent, yet water became five times costlier due to privatization. Advocates may applaud the efficiency of the model, but developing nations must emphasize accessibility and affordability of the resource. Privatization, as a model for water distribution, remains contentious.
  • Monitoring water stress using time series of observed to unstressed surface temperature differenceG. Boulet, A. Chehbouni, P. Gentine, B. Duchemin, J. Ezzahar, and R. Hadria, 2007-05-25 [+]
    Abstract: Remote sensing data in the thermal infra red (TIR) part of the spectrum provides indirect estimates of water stress – defined as a function of the ratio between actual and potential evaporation rates – at the earth surface. During the first stage of evaporation (‘‘energy limited’’ evaporation), this ratio is close to one. During the second stage of evaporation (‘‘soil controlled’’ evaporation) water stress occurs and as a result this ratio drops below one. Recently, methods using TIR data to monitor stress have shifted from establishing empirical relationships between combined vegetation cover/temperature indices and soil moisture status to data assimilation of surface temperature into complex soil–vegetation–atmosphere transfer models. However, data and expertise are often lacking to widely apply those methods. In this paper we investigate the proof-of-concept of using solely the difference between actual and unstressed surface temperature as a baseline to monitor water stress. The unstressed temperature is the equilibrium temperature of a given surface expressed in potential conditions, computed with an energy balance model. Theoretical, modeling, and experimental documentation of the proof-of-concept are shown for datasets acquired within the frame of two international experiments in semi-arid region. We show that the difference between the observed and the unstressed surface temperatures is almost linearly related to water stress. A sensitivity study is carried out to test the impact of modeling errors on the evaluation of the unstressed temperature. We found that even with inaccurate but realistic values of the surface parameters used to solve the energy balance and compute the unstressed temperature, the observed to unstressed surface temperature difference is still more relevant to detect second-stage processes than the difference between the observed surface temperature and the air temperature. The perspective of using an empirical index based on this difference is also investigated. These results are especially attractive for application based on TIR satellite imagery at a regional scale.
  • Intrinsic Sorptivity and Water Infiltration into Dry Soil at Different Degrees of SaturationK. E. Schulte, P. J. Culligan, and J. T. Germaine | Geoenvironmental Engineering, 2007 [+]
    Abstract: The sorptivity S quantifies the effect of capillarity on liquid movement in a porous material. For liquid infiltration into an initially dry material, S is a parameter that is contingent on both liquid and material properties as well as the maximum liquid content behind the infiltrating front, m. In prior work, Culligan et al. (2005) used scaling analyses to derive a dimensionless, intrinsic sorptivity S* that is constant for different liquids, Miller-similar materials and differing values of Se(av) •, the average degree of saturation behind the infiltrating front. The validity of the dimensionless S*, and an accompanying dimensionless Boltzmann transformation, was tested for different liquids by examining the horizontal infiltration profiles of water and Soltrol 220 in uniform dry sand at a constant Se(av)= 0.79. This work extends the validity testing of S* and to conditions of varying Se(av). Twenty-one distilled water horizontal infiltration experiments, with a range 0.64 • Se(av)• 0.86, 0.86, were were preform preformed in uniform dry sand packed at an average porosity n = 0.36. The results of the tests indicate an intrinsic sorptivity value of 0.121, which compares well with the value of Sav*= 0.128 reported by Culligan et al. The work also confirms that the dimensionless Boltzmann transformation can be used to generate a similarity profile for moisture content, even when infiltration takes place under different degrees of saturation.
  • Northern Hemisphere winter climate variability: Response to North American snow cover anomalies ...Stefan Sobolowski, Gavin Gong, and Mingfang Ting | Geophysical Research Letters, 2007 [+]
    Abstract: Links between autumn-winter snow anomalies over North America and winter climate parameters throughout the Northern Hemisphere are examined. GCM integrations are performed from September through February, with prescribed snow forcings over North America (NA) reflecting realistic, observed high/low autumn snow conditions. Forty-member ensemble differences reveal robust responses in surface air temperature and sea level pressure (SLP) fields. Over NA a negative temperature/ positive SLP response occurs while over Europe a positive temperature/negative SLP response emerges. Additionally, a dynamic wave response occurs in the troposphere, across NA and extending downgradient into Eurasia. The contribution of North American (NA) orography is evaluated via an additional pair of experiments in which mountains are removed. The resulting climatic response is mitigated considerably, which suggests a nonlinear coupling of thermal and mechanical forcings. Finally, possible physical pathways for the remote response are hypothesized, involving dynamical mechanisms consistent with previous studies.
  • Development of the Pan-Arctic Snowfall Reconstruction: New Land-Based Solid Precipitation ...J. E. Cherry, L.-B. Tremblay, M. Stieglitz, G. Gong, and S. J. Dery | Journal of Hydrometeorology, 2007 [+]
    Abstract: A new product, the Pan-Arctic Snowfall Reconstruction (PASR), is developed to address the problem of cold season precipitation gauge biases for the 1940–99 period. The method used to create the PASR is different from methods used in other large-scale precipitation data products and has not previously been employed for estimating pan-arctic snowfall. The NASA Interannual-to-Seasonal Prediction Project Catchment Land Surface Model is used to reconstruct solid precipitation from observed snow depth and surface air temperatures. The method is tested at four stations in the United States and Canada where results are examined in depth. Reconstructed snowfall at Dease Lake, British Columbia, and Barrow, Alaska, is higher than gauge observations. Reconstructed snowfall at Regina, Saskatchewan, and Minot, North Dakota, is lower than gauge observations, probably because snow is transported by wind out of the Prairie region and enters the hydrometeorological cycle elsewhere. These results are similar to gauge biases estimated by a water budget approach. Reconstructed snowfall is consistently higher than snowfall from the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) but does not have a consistent relationship with snowfall derived from the WMO Solid Precipitation Intercomparison Project correction algorithms. Advantages of the PASR approach include that 1) the assimilation of snow depth observations captures blowing snow where it is deposited and 2) the modeling approach takes into account physical snowpack evolution. These advantages suggest that the PASR product could be a valuable alternative to statistical gauge corrections and that arctic ground-based solid precipitation observing networks might emphasize snow depth measurements over gauges.
  • Predicting Drought on Seasonal-to-Decadal Time ScalesS. Schubert, R. Koster, M. Hoerling, R. Seager, D. Lettenmaier, A. Kumar, and D. Gutzler | Bulletin of the American Meteorological Society, 2007 [+]
    Abstract: Drought, especially prolonged multiyear drought, has tremendous societal and economic impacts on the United States and many other countries throughout the world. Estimates of the costs of drought to the United States alone range from $6 to $8 billion annually, with major droughts costing substantially more (e.g., $39 billion in 1988). In April 2003 the Western Governors’ Association, in partnership wit h t he National Oceanic and Atmospheric Administration (NOAA) wrote a report titled “Creating a drought early warning system for the 21st century: The National Integrated Drought Information System” (NIDIS 2004). The basic idea behind the National Integrated Drought Information System (NIDIS) is that it should take a proactive approach to reducing or mitigating the impacts of drought. Fundamental to this objective is improved monitoring and forecasting capabilities.
  • Early Pliocene (pre-Ice Age) El Niño-like global climate: Which El Niño?Peter Molnar and Mark A. Cane | Geosphere, 2007 [+]
    Abstract: Paleoceanographic data from sites near the equator in the eastern and western Pacific Ocean show that sea-surface temperatures, and apparently also the depth and temperature distribution in the thermocline, have changed markedly over the past ~4 m.y., from those resembling an El Niño state before ice sheets formed in the Northern Hemisphere to the present-day marked contrast between the eastern and western tropical Pacific. In addition, differences between late Miocene to early Pliocene (pre–Ice Age) paleoclimates and present-day average climates, particularly in the Western Hemisphere, resemble those associated with teleconnections from El Niño events, consistent with the image of a permanent El Niño state. Agreement is imperfect in that many differences between early Pliocene and present-day climates of parts of Africa, Asia, and Australia do not resemble the anomalies associated with canonical El Niño teleconnections. The teleconnections associated with the largest El Niño event in the past 100 yr, that in 1997–1998, do, however, reveal similar patterns of warming and the same sense, if not magnitude, of precipitation anomalies shown by differences between late Miocene-early Pliocene paleoclimates and present-day mean climates in these regions. If less consistent than those for the 1997–1998 event, temperature and precipitation anomalies correlated with the Paci? c Decadal Oscillation also mimic many differences between early Pliocene and present-day climates. These similarities suggest that the sea-surface temperature distribution in the Pacific Ocean before Ice Age time resembled most that of the 1997–1998 El Niño, with the warmest region extending into the easternmost Paci? c Ocean, not near the dateline as occurs in most El Niño events. This inference is consistent with equatorial Pacific proxy data indicating that at most a small east-west gradient in sea-surface temperature seems to have existed along the equator in late Miocene to early Pliocene time. Accordingly, such a difference in sea-surface temperatures may account for the large global differences in climate that characterized the earth before ice sheets became frequent visitors to the Northern Hemisphere.
  • The limited role of aquifer heterogeneity on metal reduction in an Atlantic coastal plain ...Mailloux B. J., S. Devlin, M. E. Fuller, T.C. Onstott, M. F. DeFlaun, K. H. Choi, M. Green-Blum, ... | Applied Geochemistry, 2007 [+]
    Abstract: Sixty push-pull experiments were conducted to determine the factors controlling Fe(III) and Mn(IV) reduction in a well-characterized, shallow, coastal plain aquifer near Oyster, VA, USA. The five multi-level samplers each equipped with 12 ports sampled a heterogeneous portion of the aquifer from 4.4 to 8 m-bgs. Each multi-level sampler (MLS) was injected with groundwater that contained NO  3 and Br  along with: (1) just groundwater (control treatment), (2) humics, (3) lactate (conducted twice) and (4) lactate plus humics. Microbially mediated Fe(III) reduction caused the aqueous FeTot concentrations to increase at every depth in the lactate treatment with signi?cant increases within 1 day even while NO  3 was present. Little change in the FeTot concentrations were observed in the control and humics treatment. Humics may have acted as an electron shuttle to increase Fe(III) reduction in the lactate plus humics treatment. The amount of Mn(IV) reduction was significantly lower than that of Fe(III) reduction. Geochemical modeling indicated that gas formation, sorption on reactive surfaces, and mineral precipitation were important processes and that Fe(III) and SO 2 4 reduction were co-occurring. Conditions were favorable for the precipitation of Fe-carbonates, Fe-sulfides and Fe-silicates. In the lactate treatment protist concentrations increased then decreased and planktonic cell concentrations steadily increased, whereas no change was observed in the control treatment. Correlations of Fe(III) reduction with physical and chemical heterogeneity were weak, probably as a result of the abundance of Fe(III) bearing minerals relative to electron donor abundance and that the push-pull test sampled a representative elemental volume that encompassed the microbial diversity within the aquifer.
  • Predictability of stream flow and rainfall based on ENSO for water resources management in Sri LankaJanaki Chandimala, Lareef Zubair | Journal of Hydrology, 2007 [+]
    Abstract: We investigate the viability of using El Nin˜o–Southern Oscillation (ENSO) and sea surface temperature (SST) data to predict seasonal stream?ow for one of the major rivers in Sri Lanka, the Kelani, using correlation analysis, contingency tables, and principal component analysis. The agricultural seasons in Sri Lanka are Yala (April–September) and Maha (October–March). The correlation between the Kelani River streamglow during Yala and ENSO indices (r = -0.41) is signi?cant at 99% level. In addition, the Kelani stream?ow during Yala has a correlation with the Central Indian Ocean SST (r = -0.40) that is also signi?cant at the 99% level. The first principal component of the Indo-Pacific Ocean SST is reminiscent of the SST associated with the ENSO mode. A prediction scheme based on this mode for the streamflow during Yala has a skill characterized by a correlation of 0.5 in a cross-validated mode. The prediction of streamflow during Maha is best carried out separately for the two halves of the season. During the El Nin˜o phase, the rainfall during Maha is enhanced during the first half of the season (October–December) and diminished in the second half (January–February). Rainfall rather than streamflow has a better relationship with ENSO from October to December. During the second half of the Maha season, rainfall declines with both warm and cold ENSO phases and any prediction scheme has to take into account this non-linear relationship. Overall, useful skill for seasonal streamflow predictions has been demonstrated for the Yala season and skill for seasonal rainfall predictions for the ?rst and second half of the Maha season has been elucidated.
  • Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North AmericaR. Seager, M. Ting, I. Held, Y. Kushnir, J. Lu, G. Vecchi, H.-P. Huang, N. Harnik, A. Leetmaa, ... | Science Magazine, 2007 [+]
    Abstract: How anthropogenic climate change will affect hydroclimate in the arid regions of southwestern North America has implications for the allocation of water resources and the course of regional development. Here we show that there is a broad consensus among climate models that this region will dry in the 21st century and that the transition to a more arid climate should already be under way. If these models are correct, the levels of aridity of the recent multiyear drought or the Dust Bowl and the 1950s droughts will become the new climatology of the American Southwest within a time frame of years to decades.
  • Climate teleconnections to Yangtze river seasonal streamflow at the Three Gorges Dam, ChinaXu K, Brown C, Kwon H, Lall U, Zhang J, Hayashi S, Chen Z | International Journal of Climatology, 2007 [+]
    Abstract: In this study, we identify climatic influences on summer monsoon inflow to the Three Gorges Dam (TGD) in the Yangtze River Basin and use indices of these influences to predict streamflow one season ahead. Summer monsoon streamflow at Yichang hydrological station (YHS) was analyzed for the period 1882-2003. Statistical analysis was used to develop a predictive model for summer streamflow using preceding climate variables. Linear correlation maps were constructed using 3-month ahead climate fields to identify regions that exhibit teleconnections with streamflow at Yichang. The analysis revealed regions in the eastern Indian and western Pacific Oceans that influence YHS streamflow. These regions and variables are consistent with those identified by previous studies of regional rainfall. In addition, snow cover in the Yangtze upland region provides predictive skill, likely due to snowmelt contributions to streamflow. A regression model for prediction using these indices provides a prediction R2 greater than 0.5, which is robust under the leave on out cross validation. A skilful prediction can provide guidance for water management in the Yangtze River Basin, e.g. the Three Gorges Dam and future projects for South-to-North water transfer.
  • North American Droughts of the Last Millenium from a Gridded Network of Tree-Ring DataCeline Herweijer, Richard Seager, Edward R. Cook, and Julien Emile-Geay | Journal of Climate, 2007 [+]
    Abstract: Drought is the most economically expensive recurring natural disaster to strike North America in modern times. Recently available gridded drought reconstructions have been developed for most of North America from a network of drought-sensitive tree-ring chronologies, many of which span the last 1000 yr. These reconstructions enable the authors to put the famous droughts of the instrumental record (i.e., the 1930s Dust Bowl and the 1950s Southwest droughts) into the context of 1000 yr of natural drought variability on the continent. We can now, with this remarkable new record, examine the severity, persistence, spatial signatures, and frequencies of drought variability over the past milllennium, and how these have changed with time. The gridded drought reconstructions reveal the existence of successive “megadroughts,” unprecedented in persistence (20–40 yr), yet similar in year-to-year severity and spatial distribution to the major droughts experienced in today’s North America. These megadroughts occurred during a 400-yr-long period in the early to middle second millennium A.D., with a climate varying as today’s, but around a drier mean. The implication is that the mechanism forcing persistent drought in the West and the Plains in the instrumental era is analagous to that underlying the megadroughts of the medieval period. The leading spatial mode of drought variability in the recontructions resembles the North American ENSO pattern: widespread drought across the United States, centered on the Southwest, with a hint of the opposite phase in the Pacific Northwest. Recently, climate models forced by the observed history of tropical Pacific SSTs have been able to successfully simulate all of the major North American droughts of the last 150 yr. In each case, cool “La Niña–like” conditions in the tropical Pacific are consistent with North American drought. With ENSO showing a pronounced signal in the gridded drought recontructions of the last millennium, both in terms of its link to the leading spatial mode, and the leading time scales of drought variability (revealed by multitaper spectral analysis and wavelet analysis), it is postulated that, as for the modern day, the medieval megadroughts were forced by protracted La Niña–like tropical Pacific SSTs. Further evidence for this comes from the global hydroclimatic “footprint” of the medieval era revealed by existing paleoclimatic archives from the tropical Pacific and ENSO-sensitive tropical and extratropical land regions. In general, this global pattern matches that observed for modern-day persistent North American drought, whereby a La Niña–like tropical Pacific is accompanied by hemispheric, and in the midlatitudes, zonal, symmetry of hydroclimatic anomalies.
  • Economic Value of Climate Variability Impacts on Coconut Production in Sri LankaM. T. N. Fernando, L. Zubair, T. S. G. Peiris, C. S. Ranasinghe, and J. Ratnasiri | AIACC Working Papers, 2007 [+]
    Abstract: This paper assesses the economic value of climate variability, employing a percentile analysis on an array of 31-years national annual coconut production data from 1971 to 2001. Of the production array, 10% and 90% percentiles have been considered respectively as lower and upper production extremes. The 60% of production departures of each year of extremes with respect to the mean production of 10% to 90% percentile were attributed to climate variability because studies show that the 60% of the variation of coconut production is explained by climate. These production deviations were then valued multiplying by free-on-board (FOB) prices of fresh coconuts. Results show that the foregone income from coconuts due to low rainfall varied between US$ 32 million to US$ 73 million while the incremental coconut income in crop glut extremes due to high rainfall varied between US$ 42 million and US$ 87 million. Results show that the climate variability causes income losses to the economy estimated at US$ 32 million to US$ 73 million in years of extreme crop shortage. And in years of extreme crop surplus, the economy realises income gains of US$ 42 million to US$ 87 million. These indicate the potential for significant economic benefits from investments in adaptations that would reduce variability in nut production which is caused by variations in climate. Further work is however needed to estimate the effectiveness and economic benefits that might be achieved from investments in adaptation.
  • Salinization of groundwater in the Nefzawa oases region, Tunisia: results of a regional-scale ...Mounira Zammouri, Tobias Siegfried, Tobias El-Fahem, Samiha Kriâa, and Wolfgang Kinzelbach | Hydrogeology Journal, 2007 [+]
    Abstract: A rise of the water salinity of the Complexe Terminal aquifer has been observed as a consequence of the increasing agricultural abstraction during the last decades. The nature of the salinization of the groundwater in the oases is far from understood. Brine from the Chott El Djerid, saline underlying aquifers, as well as agricultural drainage water may contribute to varying degree. This paper looks into all sources of contamination using hydrochemical data available from the beginning of the 1980's. Complementary water samples were taken from different drains and observation wells tapping the CT and the phreatic aquifers. The samples were analyzed with regard to chemistry, temperature, isotopes and other environmental tracers. Based on this, detailed conclusions with regard to the local salinization mechanisms are drawn. Furthermore, a finite difference model was developed to simulate the groundwater flow and contaminant transport in the oases. Calibration for the 1950 - 2000 period was carried out in order to adjust geological and chemical system parameters. The simulation of the planned extraction projects predicts a worsening of the present situation. Maintenance of present abstraction is not sufficient to reduce or stop the salinity increase.
  • North American drought: Reconstructions, causes, and consequencesEdward R. Cook, Richard Seager, Mark A. Cane, David W. Stahle | Earth-Science Reviews, 2007 [+]
    Abstracts: Severe drought is the greatest recurring natural disaster to strike North America. A remarkable network of centuries-long annual tree-ring chronologies has now allowed for the reconstruction of past drought over North America covering the past 1000 or more years in most regions. These reconstructions reveal the occurrence of past “megadroughts” of unprecedented severity and duration, ones that have never been experienced by modern societies in North America. There is strong archaeological evidence for the destabilizing influence of these past droughts on advanced agricultural societies, examples that should resonate today given the increasing vulnerability of modern water-based systems to relatively short-term droughts. Understanding how these megadroughts develop and persist is a timely scientific problem. Very recently, climate models have succeeded in simulating all of the major droughts over North America from the Civil War to the severe 1998–2004 drought in the western U.S. These numerical experiments indicate the dominating importance of tropical Pacific Ocean sea surface temperatures (SSTs) in determining how much precipitation falls over large parts of North America. Of central importance to drought formation is the development of cool “La Niña-like” SSTs in the eastern tropical Pacific region. This development appears to be partially linked to changes in radiative forcing over that region, which affects the Bjerknes feedback mechanism of the ENSO cycle there. Paradoxically, warmer conditions over the tropical Pacific region lead to the development of cool La Niña-like SSTs there, which is drought inducing over North America. Whether or not this process will lead to a greater prevalence of drought in the future as the world warms due to accumulating greenhouse gases is unclear at this time.
  • Mobilization of Arsenic during One-Year Incubations of Grey Aquifer Sands from Araihazar, BangladeshK. A. Radloff, Z. Cheng, M. W. Rahman, K. M. Ahmed, B. J. Mailloux, A. R. Juhl, P. Schlosser, and... | Environmental Science and Technology, 2007 [+]
    Abstract: Elevated As concentrations in shallow groundwater pose a major health threat in Bangladesh and similarly affected countries, yet there is little consensus on the mechanism of As release to groundwater or how it might be influenced by human activities. In this study, the rate of As release was measured directly with incubations lasting 11 months, using sediment and groundwater collected simultaneously in Bangladesh and maintained under anaerobic conditions throughout. Groundwater and grey sediment were collected as diluted slurries between 5 and 38 m depth, a range over which ambient groundwater As concentrations increased from 20 to 100 mcg L^-1. Arsenic was released to groundwater in slurries from 5 and 12 m depth at a relatively constant rate of 21 ± 4 (2 ?) and 23 ± 6 mcg As kg^-1 yr^-1, respectively. Amendment with a modest level of acetate increased the rate of As release only at 12 m (82 ± 18 mcg kg^-1 yr^-1). Although the groundwater As concentration was initially highest at 38 m depth, no release of As was observed. These results indicate that the spatial distribution of dissolved As in Bangladesh and local rates of release to groundwater are not necessarily linked. Iron release during the incubations did not occur concurrently with As release, providing further confirmation that the two processes are not directly coupled. Small periodic additions of oxygen suppressed the release of As from sediments at all three depths, which supports the notion that anoxia is a prerequisite for accumulation of As in Bangladesh groundwater.
  • Laboratory Investigations of Enhanced Sulfate Reduction as Groundwater Arsenic Remediation StrategyKeimowitz, A. R., B. J. Mailloux, P. Cole, M. Stute, H. J. Simpson, and S. N. Chillrud | Environmental Science and Technology, 2007 [+]
    Abstract: Landfills have the potential to mobilize arsenic via induction of reducing conditions in groundwater and subsequent desorption from or dissolution of arsenicbearing iron phases. Laboratory incubation experiments were conducted with materials from a landfill where such processes are occurring. These experiments explored the potential for induced sulfate reduction to immobilize dissolved arsenic in situ. The native microbial community at this site reduced sulfate in the presence of added acetate. Acetate respiration and sulfate reduction were observed concurrent with dissolved iron concentrations initially increasing from 0.6 íM (0.03 mg L-1 ) to a maximum of 111 íM (6.1 mg L-1 ) and subsequently decreasing to 0.74 íM (0.04 mg L-1 ). Dissolved arsenic concentrations initially covaried with iron but subsequently increased again as sulfide accumulated, consistent with the formation of soluble thioarsenite complexes. Dissolved arsenic concentrations subsequently decreased again from a maximum of 2 íM (148 íg L-1 ) to 0.3 íM (22 íg L-1 ), consistent with formation of sulfide mineral phases or increased arsenic sorption at higher pH values. Disequilibrium processes may also explain this second arsenic peak. The maximum iron and arsenic concentrations observed in the lab represent conditions most equivalent to the in situ conditions. These findings indicate that enhanced sulfate reduction merits further study as a potential in situ groundwater arsenic remediation strategy at landfills and other sites with elevated arsenic in reducing groundwater.
  • Citizen Involvement and Performance Management in Special-Purpose GovernmentsTanya Heikkila and Kimberley Roussin Isett | Public Administration Review, 2007 [+]
    Abstract: Performance management and citizen participation are being used by local governments to improve government accountability and responsiveness. In some cases, local governments are integrating these two trends. One area of local government in which this trend has not been assessed is special districts. h is paper uses data from a study of nine special districts in the state of Texas to fill this void. To assess citizen participation in performance management among the districts, we interviewed district managers, analyzed minutes from governing board meetings, and conducted citizen focus groups in three regions of the state. Our findings suggest that although districts may not yet be in tune with the latest performance management trends, they are making efforts to engage citizens in other ways. We recommend ways that districts can build on these experiences and more effectively incorporate citizens in the development, analysis, and reporting of performance measures.
  • El Niño as a mediator of the solar influence on climateJulien Emile-Geay, Mark Cane, Richard Seager, Alexay Kaplan, and Peter Almasi | Paleoceanography, 2007 [+]
    Abstract: Using a climate model of intermediate complexity, we simulate the response of the El Nin˜ o–Southern Oscillation (ENSO) system to solar and orbital forcing over the Holocene. Solar forcing is reconstructed from radiocarbon production rate data, using various scaling factors to account for the conflicting estimates of solar irradiance variability. As estimates of the difference since the Maunder Minimum range from 0.05% to 0.5% of the solar ‘‘constant,’’ we consider these two extreme scenarios, along with the intermediate case of 0.2%. We show that for large or moderate forcings, the low-pass-filtered east-west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing, with a short phase lag (about a decade). Wavelet analysis shows a statistically significant enhancement of the century-to-millennial-scale ENSO variability for even a moderate irradiance forcing. In contrast, the 0.05% case displays no such enhancement. Orbitally driven insolation forcing is found to produce a long-term increase of ENSO variability from the early Holocene onward, in accordance with previous findings. When both forcings are combined, the superposition is approximately linear in the strong scaling case. Overall, the sea surface temperature response is of the magnitude required, and is persistent enough, to induce important climatic perturbations worldwide. The results suggest that ENSO may plausibly have acted as a mediator between the Sun and the Earth’s climate. A comparison to key Holocene climate records, from the Northern Hemisphere subtropics and midlatitudes, shows support for this hypothesis.
  • El Niño prediction and predictabilityDake Chen and Mark A. Cane | Journal of Computational Physics, 2007 [+]
    Abstract: El Nin˜o-Southern Oscillation (ENSO) is by far the most energetic, and at present also the most predictable, short-term fluctuation in the Earth’s climate system, though the limits of its predictability are still a subject of considerable debate. As a result of over two-decades of intensive observational, theoretical and modeling efforts, ENSO’s basic dynamics is now well understood and its prediction has become a routine practice at application centers all over the world. The predictability of ENSO largely stems from the ocean–atmosphere interaction in the tropical Pacific and the low-dimensional nature of this coupled system. Present ENSO forecast models, in spite of their vast di?erences in complexity, exhibit comparable predictive skills, which seem to have hit a plateau at moderate level. However, mounting evidence suggests that there is still room for improvement. In particular, better model initialization and data assimilation, better simulation of surface heat and freshwater fluxes, and better representation of the relevant processes outside of the tropical Pacific, could all lead to improved ENSO forecasts.
  • Blueprints for Medieval hydroclimateRichard Seager, Nicholas Graham, Celine Herweijer, Arnold L. Gordon, Yochanan Kushnir, Ed Cook | Quaternary Science Reviews, 2007 [+]
    Abstract: According to tree ring and other records, a series of severe droughts that lasted for decades afflicted western North America during the Medieval period resulting in a more arid climate than in subsequent centuries. A review of proxy evidence from around the world indicates that North American megadroughts were part of a global pattern of Medieval hydroclimate that was distinct from that of today. In particular, the Medieval hydroclimate was wet in northern South America, dry in mid-latitude South America, dry in eastern Africa but with strong Nile River floods and a strong Indian monsoon. This pattern is similar to that accompanying persistent North American droughts in the instrumental era. This pattern is compared to that associated with familiar climate phenomena. The best fit comes from a persistently La Nin˜a-like tropical Pacific and the warm phase of the so-called Atlantic Multidecadal Oscillation. A positive North Atlantic Oscillation (NAO) also helps to explain the Medieval hydroclimate pattern. Limited sea surface temperature reconstructions support the contention that the tropical Pacific was cold and the subtropical North Atlantic was warm, ideal conditions for North American drought. Tentative modeling results indicate that a multi-century La Nin˜a-like state could have arisen as a coupled atmosphere–ocean response to high irradiance and weak volcanism during the Medieval period and that this could in turn have induced a persistently positive NAO state. A La Nin˜a-like state could also induce a strengthening of the North Atlantic meridional overturning circulation, and hence warming of the North Atlantic Ocean, by (i) the ocean response to the positive NAO and by shifting the southern mid-latitude westerlies poleward which (ii) will increase the salt flux from the Indian Ocean into the South Atlantic and (iii) drive stronger Southern Ocean upwelling.
  • Hemispheric-scale climate response to Northern Eurasia land surface characteristics and snow ...Gavin Gong, Judah Cohen, Dara Entekhabi, and Yan Ge | Global and Planetary Change, 2007 [+]
    Abstract: This paper presents a synopsis of recently published studies by the co-authors, which show that several land surface characteristics unique to Northern Eurasia are responsible for facilitating a causal relationship between autumn snow anomalies in this region and subsequent hemispheric winter climate patterns. The large size and extratropical location of the contiguous Eurasian land mass results in broad, continental-scale interannual snow cover extent and depth variations throughout autumn and winter, and corresponding diabatic heating anomalies. These surface anomalies occur in the presence of a large region of stationary wave activity, produced in part by the orographic barriers that separate northern/central Eurasia from southern/eastern Eurasia. This colocation of snow-forced anomalies and ambient wave energy is unique to Northern Eurasia, and initiates a teleconnection pathway involving stationary wave–mean flow interaction throughout the troposphere and stratosphere, ultimately resulting in a modulation of the winter Arctic Oscillation (AO). Complementary new results are also presented which show that partial snow cover extent or snow depth only anomalies in Northern Eurasia are insufficient to initiate the teleconnection pathway and produce a winter AO signal. This synopsis provides a useful interpretation of the earlier studies in the specific context of Northern Eurasia regional climate and environmental change.
  • Forward modeling of regional scale tree-ring patterns in the southeastern US and the recent ...KJ Anchukaitis, MN Evans, A Kaplan, EA Vaganov, MK Hughes, HD Grissino-Mayer, and MA Cane | Geophysical Research Letters, 2006 [+]
    Abstract: We use a mechanistic model of tree-ring formation to simulate regional patterns of climate-tree growth relationships in the southeastern United States. Modeled chronologies are consistent with actual tree-ring data, demonstrating that our simulations have skill in reproducing broad-scale patterns of the proxy’s response to climate variability. The model predicts that a decrease in summer precipitation, associated with a weakening Bermuda High, has become an additional control on tree ring growth during recent decades. A nonlinear response of tree growth to climate variability has implications for the calibration of tree-ring records for paleoclimate reconstructions and the prediction of ecosystem responses to climate change.
  • A simple model of the Arctic Ocean response to annular atmospheric modesBob Newton, L. Bruno Tremblay, Mark A. Cane, and Peter Schlosser | Journal of Geophysical Research, 2006 [+]
    Abstract: This paper briefly surveys areas of paleoclimate modeling notable for recent progress. New ideas, including hypotheses giving a pivotal role to sea ice, have revitalized the low-order models used to simulate the time evolution of glacial cycles through the Pleistocene, a prohibitive length of time for comprehensive general circulation models (GCMs). In a recent breakthrough, however, GCMs have succeeded in simulating the onset of glaciations. This occurs at times (most recently, 115 kyr B.P.) when high northern latitudes are cold enough to maintain a snow cover and tropical latitudes are warm, enhancing the moisture source. More generally, the improvement in models has allowed simulations of key periods such as the Last Glacial Maximum and the mid-Holocene that compare more favorably and in more detail with paleoproxy data. These models now simulate ENSO cycles, and some of them have been shown to reproduce the reduction of ENSO activity observed in the early to middle Holocene. Modeling studies have demonstrated that the reduction is a response to the altered orbital configuration at that time. An urgent challenge for paleoclimate modeling is to explain and to simulate the abrupt changes observed during glacial epochs (i.e., Dansgaard–Oescher cycles, Heinrich events, and the Younger Dryas). Efforts have begun to simulate the last millennium. Over this time the forcing due to orbital variations is less important than the radiance changes due to volcanic eruptions and variations in solar output. Simulations of these natural variations test the models relied on for future climate change projections. They provide better estimates of the internal and naturally forced variability at centennial time scales, elucidating how unusual the recent global temperature trends are.
  • Visualization of particle behavior within a porous medium: Mechanisms for particle filtration and...Joon Sik Yoon, John T. Germaine, and Patricia J. Culligan | Water Resources Research, 2006 [+]
    Abstract: A technique for visualizing particle transport in the interior of a porous medium is presented. The technique, which includes the construction of a translucent medium and the use of laser-induced fluorescence for particle tracking, was used to examine the behavior of a dilute suspension of negatively charged, micron-sized particles in the interior of uniform glass bead packs during one-dimensional, downward flow. Particle behavior as a function of pore fluid velocity and bead surface roughness was observed at both the macroscopic and microscopic levels. Experimental results show that particle filtration occurred only at solid-solid contact points (contact filtration) in smooth bead packs, while particle filtration occurred at the top of bead surfaces (surface filtration) as well as at solid-solid contact points in rough bead packs. Particle contact filtration was the result of physical straining at solid-solid contact points, while surface filtration was the result of particles interlocking on surface asperities. In both smooth and rough bead packs the filtration capacity of the medium decreased with the pore fluid velocity. In smooth bead packs the filtration capacity was approximately invariant with transport distance, while in the rough bead packs the filtration capacity showed a decrease with transport distance. This decrease was attributed to the early surface filtration of larger particles as a result of gravitational sedimentation. The accumulation of reversibly attached particles was observed even when particle pore fluid concentrations were stable.
  • Predictability Loss in an Intermediate ENSO Model due to Initial Error and Atmospheric NoiseAlicia R. Karspeck, Alexey Kaplan, and Mark A. Cane | Journal of Climate, 2006 [+]
    Abstract: The seasonal and interannual predictability of ENSO variability in a version of the Zebiak–Cane coupled model is examined in a perturbation experiment. Instead of assuming that the model is “perfect,” it is assumed that a set of optimal initial conditions exists for the model. These states, obtained through a nonlinear minimization of the misfit between model trajectories and the observations, initiate model forecasts that correlate well with the observations. Realistic estimates of the observational error magnitudes and covariance structures of sea surface temperatures, zonal wind stress, and thermocline depth are used to generate ensembles of perturbations around these optimal initial states, and the error growth is examined. The error growth in response to subseasonal stochastic wind forcing is presented for comparison. In general, from 1975 to 2002, the large-scale uncertainty in initial conditions leads to larger error growth than continuous stochastic forcing of the zonal wind stress fields. Forecast ensemble spread is shown to depend most on the calendar month at the end of the forecast rather than the initialization month, with the seasons of greatest spread corresponding to the seasons of greatest anomaly variance. It is also demonstrated that during years with negative (and rapidly decaying) Niño-3 SST anomalies (such as the time period following an El Niño event), there is a suppression of error growth. In years with large warm ENSO events, the ensemble spread is no larger than in moderately warm years. As a result, periods with high ENSO variance have greater potential prediction utility. In the realistic range of observational error, the ensemble spread has more sensitivity to the initial error in the thermocline depth than to the sea surface temperature or wind stress errors. The thermocline depth uncertainty is the principal reason why initial condition uncertainties are more important than wind noise for ensemble spread.
  • Artificial neural networks and multicriterion analysis for sustainable irrigation planningK. Srinivasa Raju, D. Nagesh Kumar, and Lucien Duckstein | Computers and Operations Research, 2006 [+]
    Abstract: The objective of the present paper is to select the best compromise irrigation planning strategy for the case study of Jayakwadi irrigation project, Maharashtra, India. Four-phase methodology is employed. In phase 1, separate linear programming (LP) models are formulated for the three objectives, namely, net economic benefits, agricultural production and labour employment. In phase 2, nondominated (compromise) irrigation planning strategies are generated using the constraint method of multiobjective optimisation. In phase 3, Kohonen neural networks (KNN) based classification algorithm is employed to sort nondominated irrigation planning strategies into smaller groups. In phase 4, multicriterion analysis (MCA) technique, namely, Compromise Programming is applied to rank strategies obtained from phase 3. It is concluded that the above integrated methodology is effective for modeling multiobjective irrigation planning problems and the present approach can be extended to situations where number of irrigation planning strategies are even large in number.
  • The Source of Europe's Mild Climate: The notion that the Gulf Stream is responsible for keeping ...Richard Seager | American Scientist, 2006 [+]
    Abstract: If you grow up in England, as I did, a few items of unquestioned wisdom are passed down to you from the preceding generation. Along with stories of a plucky island race with a glorious past and the benefits of drinking unbelievable quantities of milky tea, you will be told that England is blessed with its pleasant climate courtesy of the Gulf Stream, that huge current of warm water that flows northeast across the Atlantic from its source in the Gulf of Mexico. That the Gulf Stream is responsible for Europe’s mild winters is widely known and accepted, but, as I will show, it is nothing more than the earth-science equivalent of an urban legend.
  • Locally weighted polynomial regression: Parameter choice and application to forecasts of the ...Lall U., Y.-I. Moon, H.-H. Kwon, K. Bosworth | Water Resources Research, 2006 [+]
    Abstract: Relationships between hydrologic variables are often nonlinear. Usually, the functional form of such a relationship is not known a priori. A multivariate, nonparametric regression methodology is provided here for approximating the underlying regression function using locally weighted polynomials. Locally weighted polynomials consider the approximation of the target function through a Taylor series expansion of the function in the neighborhood of the point of estimate. Cross-validatory procedures for the selection of the size of the neighborhood over which this approximation should take place and for the order of the local polynomial to use are provided and shown for some simple situations. The utility of this nonparametric regression approach is demonstrated through an application to nonparametric short-term forecasts of the biweekly Great Salt Lake volume. Blind forecasts up to 1 year in the future using the 1847–2004 time series of the Great Salt Lake are presented.
  • Measuring International Policy PerformanceTobias Siegfried and Thomas Bernauer | Swiss Federal Institute of Technology Zürich, 2006
  • Water and Economic Development: The Role of Interannual Variability and a Framework for ResilienceBrown, C. and U. Lall | Natural Resources Forum, 2006 [+]
    Abstract: The article advances the hypothesis that the seasonal and inter-annual variability of rainfall is a significant and measurable factor in the economic development of nations. An analysis of global datasets reveals a statistically significant relationship between greater rainfall variability and lower per capita GDP. Having established this correlation, we construct a water resources development index that highlights areas that have the greatest need for storage infrastructure to mitigate the impacts of rainfall variability on water availability for food and basic livelihood. The countries with the most critical infrastructure needs according to this metric are among the poorest in the world, and the majority of them are located in Africa. The importance of securing water availability in these nations increases every day in light of current population growth, economic development, and climate change projections.
  • Comparing Collaborative Mechanisms in Large-Scale Economic GovernanceAndrea K. Gerlak and Tanya Heikkila | Natural Resources Journal, 2006 [+]
    Abstract: Collaborative approaches to environmental and natural resource management are on the rise in the United States. This article examines collaborative governance in four high-profile and large-scale ecosystems: the Northwest Power and Conservation Council's Fish and Wildlife Program in the Columbia River Basin, the Chesapeake Bay Program, the CALFED Bay-Delta Program in California's San Francisco Bay/Sacramento San Joaquin River Delta, and the Florida Everglades Restoration Program. We compare the governance structures of these four institutional arrangements by examining how collaboration occurs or is organized at three different levels of decision making: constitutional, collective choice (or policymaking), and operational (or implementation). This includes an examination of governance and advisory bodies as well as coordinating and monitoring structures.
  • Comparing Collaborative Mechanisms in Large-Scale Ecosystem GovernanceGerlak, A.K. and T. Heikkila | Natural Resources Journal, 2006 [+]
    Abstract: Collaborative approaches to environmental and natural resource management are on the rise in the United States. This article examines collaborative governance in four high-profile and large-scale ecosystems: the Northwest Power and Conservation Council's Fish and Wildlife Program in the Columbia River Basin, the Chesapeake Bay Program, the CALFED Bay-Delta Program in California's San Francisco Bay/SacramentoSan Joaquin River Delta, and the Florida Everglades Restoration Program. We compare the governance structures of these four institutional arrangements by examining how collaboration occurs or is organized at three different levels of decision making: constitutional, collective choice (or policymaking), and operational (or implementation). This includes an examination of governance and advisory bodies as well as coordinating and monitoring structures.
  • Natural Disaster Risks in Sri Lanka: Mapping Hazards and Risk HotspotsLareef Zubair and Vidhura Ralapanawe, Upamala Tennakoon, Zeenas Yahiya, and Ruvini Perera | Natural Disaster Hotspots Case Studies, 2006 [+]
    Abstract: The goals for this case study of natural disasters in Sri Lanka were (1) to examine the methodologies needed for subnational assessments of hazard, vulnerability, and hotspots; (2) to assess the interplay among hazards and vulnerability; and (3) to assess the consequence of combinations of multiple hazards and vulnerability factors. In the terminology used here, a “natural disaster” occurs when the impact of a hazard is borne by “elements at risk” that may be vulnerable to the hazard. The elements considered in this study are simplified into categories of people, infrastructure, and economic activities.
  • Optimal Reservoir Operation Using Multi-Objective Evolutionary AlgorithmM. Janga Reddy and D. Nagesh Kumar | Water Resources Management, 2006 [+]
    Abstract: This paper presents a Multi-objective Evolutionary Algorithm (MOEA) to derive a set of optimal operation policies for a multipurpose reservoir system. One of the main goals in multiobjective optimization is to find a set of well distributed optimal solutions along the Pareto front. Classical optimization methods often fail in attaining a good Pareto front. To overcome the drawbacks faced by the classical methods for Multi-objective Optimization Problems (MOOP), this study employs a population based search evolutionary algorithm namely Multi-objective Genetic Algorithm (MOGA) to generate a Pareto optimal set. The MOGA approach is applied to a realistic reservoir system, namely Bhadra Reservoir system, in India. The reservoir serves multiple purposes irrigation, hydropower generation and downstream water quality requirements. The results obtained using the proposed evolutionary algorithm is able to offer many alternative policies for the reservoir operator, giving fiexibility to choose the best out of them. This study demonstrates the usefulness of MOGA for a real life multi-objective optimization problem.
  • Progress in Paleoclimate ModelingM. A. Cane, P. Braconnot, A. Clement, H. Gildor, S. Joussaume, M. Kageyama, ... | Journal of Climate, 2006 [+]
    Abstract: This paper briefly surveys areas of paleoclimate modeling notable for recent progress. New ideas, including hypotheses giving a pivotal role to sea ice, have revitalized the low-order models used to simulate the time evolution of glacial cycles through the Pleistocene, a prohibitive length of time for comprehensive general circulation models (GCMs). In a recent breakthrough, however, GCMs have succeeded in simulating the onset of glaciations. This occurs at times (most recently, 115 kyr B.P.) when high northern latitudes are cold enough to maintain a snow cover and tropical latitudes are warm, enhancing the moisture source. More generally, the improvement in models has allowed simulations of key periods such as the Last Glacial Maximum and the mid-Holocene that compare more favorably and in more detail with paleoproxy data. These models now simulate ENSO cycles, and some of them have been shown to reproduce the reduction of ENSO activity observed in the early to middle Holocene. Modeling studies have demonstrated that the reduction is a response to the altered orbital configuration at that time. An urgent challenge for paleoclimate modeling is to explain and to simulate the abrupt changes observed during glacial epochs (i.e., Dansgaard–Oescher cycles, Heinrich events, and the Younger Dryas). Efforts have begun to simulate the last millennium. Over this time the forcing due to orbital variations is less important than the radiance changes due to volcanic eruptions and variations in solar output. Simulations of these natural variations test the models relied on for future climate change projections. They provide better estimates of the internal and naturally forced variability at centennial time scales, elucidating how unusual the recent global temperature trends are.
  • Unraveling the Mystery of Indian Monsoon Failure During El NiñoK. Krishna Kumar, Balaji Rajagopalan, Martin Hoerling, Gary Bates, and Mark Cane | Science Magazine, 2006 [+]
    Abstract: The 132-year historical rainfall record reveals that severe droughts in India have always been accompanied by El Nin˜o events. Yet El Nin˜o events have not always produced severe droughts. We show that El Nin˜o events with the warmest sea surface temperature (SST) anomalies in the central equatorial Pacific are more effective in focusing drought-producing subsidence over India than events with the warmest SSTs in the eastern equatorial Pacific. The physical basis for such different impacts is established using atmospheric general circulation model experiments forced with idealized tropical Pacific warmings. These findings have important implications for Indian monsoon forecasting.
  • Ant Colony Optimization for Multi-Purpose Reservoir OperationD. Nagesh Kumar and M. Janga Reddy | Water Resources Management, 2006 [+]
    Abstract: In this paper a metaheuristic technique called Ant Colony Optimization (ACO) is proposed to derive operating policies for a multi-purpose reservoir system. Most of the real world problems often involve non-linear optimization in their solution with high dimensionality and large number of equality and inequality constraints. Often the conventional techniques fail to yield global optimal solutions. The recently proposed evolutionary algorithms are also facing problems, while solving large-scale problems. In this study, it is intended to test the usefulness of ACO in solving such type of problems. To formulate the ACO model for reservoir operation, the problem is approached by considering a ?nite time series of inflows, classifying the reservoir volume into several class intervals, and determining the reservoir release for each period with respect to a predefined optimality criterion. The ACO technique is applied to a case study of Hirakud reservoir, which is a multi-purpose reservoir system located in India. The multiple objectives comprise of minimizing flood risks, minimizing irrigation deficits and maximizing hydropower production in that order of priority. The developed model is applied for monthly operation, and consists of two models viz., for short-time horizon operation and for longtime horizon operation. To evaluate the performance of ACO, the developed models are also solved using real coded Genetic Algorithm (GA). The results of the two models indicate that ACO model performs better, in terms of higher annual power production, while satisfying irrigation demands and flood control restrictions, compared to those obtained by GA. Finally it is found that ACO model outperforms GA model, especially in the case of long-time horizon reservoir operation.
  • The Strengthening Relationship between ENSO and Northeast Monsoon Rainfall over Sri Lanka and ...Lareef Zubair and C. F. Ropelewski | Journal of Climate, 2006 [+]
    Abstract: Recently, it was reported that the relationship of the Indian southwest monsoon rainfall with El Niño– Southern Oscillation (ENSO) has weakened since around 1980. Here, it is reported that in contrast, the relationship between ENSO and the northeast monsoon (NEM) in south peninsular India and Sri Lanka from October to December has not weakened. The mean circulation associated with ENSO over this region during October to December does not show the weakening evident in the summer and indeed is modestly intensified so as to augment convection. The intensification of the ENSO–NEM rainfall relationship is modest and within the historical record but stands in contrast to the weakening relationship in summer. The intensification of the circulation is consistent with the warming of surface temperatures over the tropical Indian Ocean in recent decades. There is modestly intensified convection over the Indian Ocean, strengthening of the circulation associated with ENSO (Walker circulation), and enhanced rainfall during El Niño episodes in a manner consistent with an augmented ENSO–NEM relationship.
  • Effect of Forecast-Based Pricing on Irrigated Agriculture: A SimulationCasey Brown and Peter Rogers | Journal of Water Resources Planning and Management, 2006 [+]
    Abstract: : Seasonal climate prediction offers potentially useful information for water managers. However, implementing forecast information is challenging due to the probabilistic nature of forecasts and limited demonstrations of usefulness. In this study, an adaptive groundwater pricing model utilizing operational seasonal climate forecasts was evaluated for groundwater management. The price for groundwater in the upcoming season was selected according to an algorithm that incorporates the current groundwater elevation and a prediction of seasonal rainfall. A simulation based on 37 years of rainfall data and operational monsoon forecasts for Tamil Nadu, India, was conducted to assess the effect of forecast-based pricing on societal benefits, groundwater elevation, and farmer income. Results indicate the adaptive pricing model is far more effective at maintaining groundwater elevations and maximizing societal benefits than a static groundwater price. Current groundwater elevation was a more effective input to the pricing algorithm than the forecast of seasonal rainfall when evaluated separately. A comparison of forecast use by water managers to select prices and use by farmers to choose crop patterns found similar societal benefits for each approach. Controlling demand for groundwater through pricing will cause hardship for current groundwater users who currently access groundwater without tariffs. Water managers should consider using tariff revenue to provide drought relief and transitional assistance.
  • Hydroclimatic association of the monthly summer monsoon rainfall over India with large-scale ...Rajib Maity and D. Nagesh Kumar | Atmospheric Science Letters, 2006 [+]
    Abstract: The hydroclimatic association between the monthly Indian summer monsoon rainfall and a proposed monthly composite index (MCI) of large-scale atmospheric circulations from the Pacific Ocean and Indian Ocean regions is established. The spatial variability of this association is also checked. The predictability of the monthly Indian summer monsoon rainfall using the MCI is also investigated and is seen to be encouraging.
  • Solar Forcing of the tropical Pacific climate and impacts over North America for the last milleniumAmy C. Clement, Julien Emile-Geay, Richard Seager, Mark Cane, and Michael N. Evans | PAGES News , 2006 [+]
    Abstract: It is now well known that the state of the tropical Pacific climate has a large influence on the global climate, as evidenced by the inter-annual variations associated with the El Nino/Southern Oscillation (ENSO) and its global teleconnections. If the mean state of the tropical Pacific were to undergo shifts on longer timescales, it is likely that such changes would also have global impacts. This possibility has prompted debate about whether the tropical Pacific has undergone changes over the 20th century that are akin to the warm phase (El Nino) or cold phase (La Nina) of ENSO, and also whether such shifts will be part of the climate response to increased greenhouse gases (GHGs) in the future. At present, state-of-the-art coupled ocean atmosphere general circulation models (GCMs) simulate different responses in the tropical Pacific climate to increased GHGs, with some models predicting a decreased east/west sea surface temperature (SST) gradient (akin to El Nino), others predicting no Change (Collins et al., 2005). Given this uncertainty, it is reasonable to turn to the past to learn about how the tropical Pacific responded to climate forcing, and whether the influence of the tropical Pacific can be seen in past regional climate proxies around the globe.
  • Impacts of Considering Climate Variability on Investment Decisions in EthiopiaPaul J. Block, Kenneth Strzepek, Mark Rosegrant, and Xinshen Diao | International Food Policy Institute, 2006 [+]
    Abstract: Extreme interannual variability of precipitation within Ethiopia is not uncommon, inducing droughts or floods and often creating serious repercussions on agricultural and nonagricultural commodities. An agro-economic model, including mean climate variables, was developed to assess irrigation and road construction investment strategies in comparison to a baseline scenario over a 12-year time horizon. The motivation for this work is to evaluate whether the inclusion of climate variability in the model has a significant effect on prospective investment strategies and the resulting country-wide economy. The mean climate model is transformed into a variable climate model by dynamically adding yearly climate-yield factors, which influence agricultural production levels and linkages to non-agricultural goods. Nine sets of variable climate data are processed by the new model to produce an ensemble of potential economic prediction indicators. Analysis of gross domestic product and poverty rate reveal a significant overestimation of the country’s future welfare by the mean climate model method, in comparison to probability density functions created from the variable climate ensemble. The ensemble is further utilized to demonstrate risk assessment capabilities. The addition of climate variability to the agro-economic model provides a framework, including realistic ranges of economic values, from which Ethiopian planners may make strategic decisions.
  • Sorptivity and liquid infiltration into dry soilPatricia J. Culligan, Vladimir Ivanov, and John T. Germaine | Advances in Water Resources , 2005 [+]
    Abstract: The sorptivity S quantifies the effect of capillarity on liquid movement in a porous material. For liquid infiltration into an initially dry material, S is a parameter that is contingent on both liquid and material properties as well as the maximum liquid content behind the infiltrating front, hm. Scaling analyses are used to derive a dimensionless, intrinsic sorptivity S* that is constant for different liquids, Miller-similar materials and different values of hm. The analyses confirm that S is dependent on b^1/2, where b = cos/ is a measure of the wettability of the liquid. They also indicate a power law relationship between S and Se(av) , the average liquid saturation behind the infiltrating front. Seventeen water and eleven Soltrol 220 horizontal infiltration experiments are reported in uniform, dry sand. Test results show that water is partially wetting in the sand. They also confirm that S varies as S^d where d = 3.2 for the experimental conditions. The usefulness of a general, dimensionless Boltzmann variable is demonstrated to normalize infiltration profiles for the different liquids. An approximate method for sorptivity calculation is shown to provide an accurate estimate of S*.
  • Decadal to century scale trends in North American snow extent in coupled atmosphere-ocean ... modelsAllan Frei and Gavin Gong | Geophysical Research Letters 2005, 2005 [+]
    Abstract: 20th and 21st century decadal scale trends and variability in winter North American snow cover extent (NA-SCE) are investigated using coupled atmosphere-ocean general circulation model experiments participating in the upcoming Intergovernmental Panel on Climate Change Fourth Assessment Report. Significant between-model variability is found, with most models underestimating mean NA-SCE. 20th century simulations are poorly correlated with observations, and, while individual ensemble members capture the magnitude of decadal scale variability, the variability of the signal is dampened in the ensemble mean, indicating that decadal-scale NA-SCE variability is associated predominantly with internal model variability rather than external forcing. Two 21st century emission scenarios with realistic (moderate or significant) greenhouse gas emission rates produce decreasing NA-SCE trends, while one unrealistic scenario with fixed concentrations produces little or no NA-SCE trend. These results suggest that snow cover may be a sensitive indicator of climate change, and that North American snow extent will probably decrease in response to greenhouse gas emissions, although the magnitude of the response may be nonlinear.
  • Optimal Utilization of a Non-Renewable Transboundary Groundwater Resource - Methodology, Case ...Tobias Ulrich Siegfried | Swiss Federal Institute of Technology Zürich, 2005 [+]
    Abstract: The North-West Sahara Aquifer System (NWSAS) is one of the largest groundwater systems of the world. It consists of two main aquifers, the Terminal Complex (TC) and the underlying Intercalary Continental (IC), and covers in total an area of more than 10 6 km2 . Present day recharge is approximately 30 m3 /s and only of local importance in the Saharan Atlas. The natural system is draining into the topographic lows of the endorheic basin, the Chotts. It is used as a resource by three countries, Algeria, Tunisia and Libya. The bulk of the water pumped from the system is utilized for the irrigation of approximately 14’000 km2 of agricultural land. The present situation can be characterized as fossil groundwater mining, the total abstraction being 80 m3 /s. While the stored amount of water would be able to sustain this abstraction for another 10’000 years, the water comes at a price. On one hand there is the cost of pumping and the investment for wells and pipelines. On the other hand the cones of depression created by the pumping lead to a deterioration of the water quality due to attraction of saline waters from di?erent sources such as the brine of the Chotts, the saline water of the underlying Turonian and the seawater of the Mediterranean. In order to avert excessive prices for water and deterioration of the resource on the whole, a common management scheme for the three countries has to be found. In an effort towards such a scheme, a mathematical model of the NWSAS was developed. It is a groundwater flow model on the basis of a finite difference method. The model demonstrates that with the required total pumping rate by 2050 large areas of the presently strongly pumped regions will face a piezometric decline with economically infeasible drawdowns of more than 200 m below ground level. A redistribution of the pumped quantity so as to minimize water provision costs seems interesting to explore. For that purpose, the groundwater model was coupled with optimization algorithms to find allocation patterns that conform to demand, drawdown and quality constraints in time while minimizing overall provision costs. The wells in an optimal scheme spread out over the area to equilibrate distribution cost with pumping cost, which depends on drawdown. They further spread to the IC from the TC and the pumping scheduling is characterized by oscillation between well?elds. The results demonstrate among other things that cooperating in devising internationally coordinated pumping schemes is advantageous for the three countries. Besides the global management task for the whole basin a number of subproblems on a more local scale arise. For that purpose, the Nefzawa oases region is studied. Over the last fifty years, the pumped quantity in the Nefzawa has been increased sixfold while the irrigated area tripled. As a consequence, the salinity of pumped water has increased locally to unacceptable values. An econometric estimation of the farm– level technical inefficiencies in agricultural production revealed that the farmers in the Nefzawa produce well below their potential agricultural output. Governmentally induced educational measures could allow to increase production without further increasing the amount of irrigation water applied. To study salination, a detailed flow and transport model embedded in the regional NWSAS model has been developed. It was shown, that agricultural drainage waters that are highly enriched in TDS pollute the TC aquifer by leaching in cases where the confining unit of the TC shows structural weakness. Such drainage typically is channeled from the oases to nearby local terrain depressions. It seems crucial to improve the management of this drainage network so as to prevent further salination of the TC aquifer.
  • Fuzzy Multicriterion Decision Making in Irrigation PlanningK. Srinivasa Raju and D. Nagesh Kumar | Irrigation and Drainage, 2005 [+]
    Abstract: Multicriterion decision making (MCDM) has emerged as an effective methodology due to its ability to combine quantitative and qualitative criteria for selection of the best alternative. Concurrently, fuzzy logic is gaining importance due to its glexibility in handling imprecise subjective data. In the present study two fuzzy logic-based MCDM methods, namely similarity analysis (SA) and decision analysis (DA), are adopted and developed as a FUzzy Decision System (FUDS) and applied to a case study of the Sri Ram Sagar Project (SRSP), Andhra Pradesh, India, for selecting the best-performing irrigation subsystem. It is found that both SA and DA suggested the same irrigation subsystem as the best. It is concluded that application of fuzzy logic methodology for real-world decision-making problems is found to be effective.
  • Why Are There Tropical Warm Pools?Clement, A. C., R. Seager, and R. Murtugudde | Journal of Climate, 2005 [+]
    Abstract: Tropical warm pools appear as the primary mode in the distribution of tropical sea surface temperature (SST). Most previous studies have focused on the role of atmospheric processes in homogenizing temperatures in the warm pool and establishing the observed statistical SST distribution. In this paper, a hierarchy of models is used to illustrate both oceanic and atmospheric mechanisms that contribute to the establishment of tropical warm pools. It is found that individual atmospheric processes have competing effects on the SST distribution: atmospheric heat transport tends to homogenize SST, while the spatial structure of atmospheric humidity and surface wind speeds tends to remove homogeneity. The latter effects dominate, and under atmosphere-only processes there is no warm pool. Ocean dynamics counter this effect by homogenizing SST, and it is argued that ocean dynamics is fundamental to the existence of the warm pool. Under easterly wind stress, the thermocline is deep in the west and shallow in the east. Because of this, poleward Ekman transport of water at the surface, compensated by equatorward geostrophic flow below and linked by equatorial upwelling, creates a cold tongue in the east but homogenizes SST in the west, creating a warm pool. High clouds may also homogenize the SST by reducing the surface solar radiation over the warmest water, but the strength of this feedback is quite uncertain. Implications for the role of these processes in climate change are discussed.
  • Pathways into the Pacific Equatorial Undercurrent: A Trajectory AnalysisPaul J. Goodman, Wilco Hazeleger, Pedro de Vries, and Mark Cane | Journal of Physical Oceanography, 2005 [+]
    Abstract: A time-dependent trajectory algorithm is used to determine the sources of the Pacific Equatorial Undercurrent (EUC) in a global climate model with 1/4 degree (eddypermitting) resolution and forced with realistic winds. The primary sources and pathways are identified and the transformation of properties in temperature/salinity space are explored. An estimate for the quantity of recirculation, a notoriously difficult property to estimate from observational data, is given. Over two-thirds of the water in the Pacific EUC at 140°W originates south of the equator. 70% of the EUC is ventilated outside of the tropics (poleward of 13°S or 10°N): three quarters of these extratropical trajectories travel through the western boundary currents between their subduction and incorporation into the EUC and one fifth of the extratropical trajectories enter and leave the tropical band at least once before entering the EUC.
  • The Formation of Large-scale Collaborative Resource Management Institutions: Clarifying Roles of ...Tanya Heikkila and Andrea K. Gerlak | Policy Studies Journal , 2005 [+]
    Abstract: This article explores the emergence of collaborative institutional arrangements for managing natural resources in large-scale and complex resource settings, among numerous political jurisdictions and stakeholders. It examines four regional institutions in the United States: the Northwest Power and Conservation Council’s Fish and Wildlife Program, the Chesapeake Bay Program, the CALFED BayDelta Program, and the Comprehensive Everglades Restoration Plan. While a wealth of literature has looked at the emergence of smaller-scale resource management institutions, and some literature has begun to look at the characteristics and successes of these regional institutions, theory is lacking to explain the formation of these regional institutions. We first introduce three relevant streams of literature—on common pool resources management, on policy entrepreneurs and social capital, and on science and information in policy change—to frame our analysis. The comparisons of the cases point to the importance of integrating key insights from the literature for understanding the formation of collaborative resource governance. We emphasize how science, leadership, and prior organizational experience interact in facilitating institutional change, particularly in the process of raising awareness about resource management problems. In tracing the formation of these institutions, we also identify how external institutional triggers can help spur collaborative governance.
  • Modernisation of Sri Lanka Traditional Irrigation Systems and SustainabilityLareef Zubair | Science Technology Society, 2005 [+]
    Abstract: Arnold Toynbee described the ancient irrigation system of Sri Lanka as an amazing system of irrigated agriculture, which developed over a millennium. It was partially transformed during its encounter with British colonialism with new values, technological systems, administrative structures and a legal code. After the independence in 1948, this transformation continued with foreign aid and technical expertise from the West. The shortcomings of modern irrigation systems with respect to planning, policy and sustainability are now recognised (WCDD 2000). Here, it is argued that the indigenous irrigation systems in Sri Lanka offer a useful counterpoint of one that has been sustained and had many favourable attributes. There are lessons to be learnt from contrasting different modes of irrigation practice in the light of sustainability.
  • Modeling of Tropical Forcing of Persistent Droughts and Pluvials over Western North America: ...Richard Seager, Yochanan Kushnir, Celine Herweijer, Naomi Naik, and Jennifer Vellez | Journal of Climate, 2005 [+]
    Abstract: The causes of persistent droughts and wet periods, or pluvials, over western North America are examined in model simulations of the period from 1856 to 2000. The simulations used either (i) global sea surface temperature data as a lower boundary condition or (ii) observed data in just the tropical Pacific and computed the surface ocean temperature elsewhere with a simple ocean model. With both arrangements, the model was able to simulate many aspects of the low-frequency (periods greater than 6 yr) variations of precipitation over the Great Plains and in the American Southwest including much of the nineteenthcentury variability, the droughts of the 1930s (the “Dust Bowl”) and 1950s, and the very wet period in the 1990s. Results indicate that the persistent droughts and pluvials were ultimately forced by persistent variations of tropical Pacific surface ocean temperatures. It is argued that ocean temperature variations outside of the tropical Pacific, but forced from the tropical Pacific, act to strengthen the droughts and pluvials. The persistent precipitation variations are part of a pattern of global variations that have a strong hemispherically and zonally symmetric component, which is akin to interannual variability, and that can be explained in terms of interactions between tropical ocean temperature variations, the subtropical jets, transient eddies, and the eddy-driven mean meridional circulation. Rossby wave propagation poleward and eastward from the tropical Pacific heating anomalies disrupts the zonal symmetry, intensifying droughts and pluvials over North America. Both mechanisms of tropical driving of extratropical precipitation variations work in summer as well as winter and can explain the year-round nature of the precipitation variations. In addition, land–atmosphere interactions over North America appear important by (i) translating winter precipitation variations into summer evaporation and, hence, precipitation anomalies and (ii) shifting the northward flow of moisture around the North Atlantic subtropical anticyclone eastward from the Plains and Southwest to the eastern seaboard and western Atlantic Ocean.
  • Mechanisms of ENSO-forcing of hemispherically symmetric precipitation variabilityR. Seager, N. Harnik, W. A. Robinson, Y. Kushnir, M. Ting, H.-P. Huang, and J. Velez | Quarterly Journal of the Royal Meteorological Society, 2005 [+]
    Abstract: The patterns of precipitation anomalies forced by the El Ni˜no–Southern Oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and, in the midlatitudes, have a prominent zonally symmetric component. Observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically-forced changes in the subtropical jets. During El Ni˜no events the jets strengthen in each hemisphere and shift equatorward. Changes in the subtropical jet influence the transient-eddy momentum fluxes and the eddy-driven mean meridional circulation. During El Ni˜no events, eddy-driven ascent in the midlatitudes of each hemisphere is accompanied by low-level convergence and brings increased precipitation. These changes in the transient-eddy and stationary-eddy moisture fluxes almost exactly cancel each other and, in sum, do not contribute to the zonal-mean precipitation anomalies. Propagation of anomalous stationary waves disrupts the zonal symmetry. Flow around the deeper Aleutian Low and the eastward extension of the Pacific jet stream supply the moisture for increased precipitation over the eastern North Pacific and the western seaboard of the United States, while transient-eddy moisture convergence supplies the moisture for increased precipitation over the southern United States. In each case, increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes.
  • The 1976/77 transition in precipitation over the Americas and the influence of tropical sea ...Huei-Ping Huang, Richard Seager and Yochanan Kushnir | Climate Dynamics, 2005 [+]
    Abstract: Most major features of the interdecadal shift in boreal winter-spring precipitation over the American continents associated with the 1976–1977 transition are reproduced in atmospheric general circulation model (GCM) simulations forced with observed sea surface temperature (SST). The GCM runs forced with global and tropical Pacific SSTs produce similar multidecadal changes in precipitation, indicating the dominant influence of tropical Pacific SST. Companion experiments indicate that the shift in mean conditions in the tropical Pacific is responsible for these changes. The observed and simulated ‘‘post- minus pre-1976’’ difference in Jan– May precipitation is wet over Mexico and the southwest U.S., dry over the Amazon, wet over sub-Amazonian South America, and dry over the southern tip of South America. This pattern is not dramatically different from a typical El Nin˜o-induced response in precipitation. Although the interdecadal (post- minus pre-1976) and interannual (El Nin˜oLa Nin˜a) SST anomalies differ in detail, they produce a common tropics-wide tropospheric warmth that may explain the similarity in the precipitation anomaly patterns for these two time scales. An analysis of local moisture budget shows that, except for Mexico and the southwest U.S. where the interdecadal shift in precipitation is balanced by evaporation, elsewhere over the Americas it is balanced by a shift in low-level moisture convergence. Moreover, the moisture convergence is due mainly to the change in low-level wind divergence that is linked to low-level ascent and descent.
  • Optimizing experimental design to estimate ammonia and nitrite oxidation biokinetic parameters ...Kartik Chandran, and Barth F. Smets | Water Research, 2005 [+]
    Abstract; Knowledge of relative NH4+–N to NO2–N oxidation and NO2–N to NO3–N oxidation dynamics is essential before application of either single-step or two-step nitri?cation models to fit batch nitrification respirograms. We have previously shown that two step nitrification models based on respirometry permit the estimation of kinetic parameters for both nitrification steps from a single respirogram associated with NH4+–N to NO3–N oxidation. However, two-step model parameter estimates are meaningful only under circumstances when the respirograms contain sufficient kinetic information pertaining to both steps. In this study, we present an operationally amenable extant batch nitri?cation respirometric assay to engender maximal information content in the resulting respirograms with respect to both constituent nitrification steps. The developed design consists of an initial NH4+–N pulse to a nitrifying biomass sample followed by an additional NO2–N pulse at an optimal time point, which can be rigorously determined by maximizing the value of the determinant of the Fisher information matrix, Det(F) or, alternatively, by visually identifying the point of NH4+–N depletion during the respirometric assay. The proposed design is applicable for accurate determination of the Monod kinetic parameter estimates for both nitri?cation steps from batch respirograms even when the pseudo-first order rate coefficients for the two nitri?cation steps are nearly equal; a condition under which standard NH4+–N to NO3–N respirograms typically lack information with respect to NO2–N oxidation.
  • Tropical Pacific-Driven Decadal Energy Transport VariabilityHezeleger, W. and Severijns, C., R. Seager, and F. Molteni | Journal of Climate , 2005 [+]
    Abstract: The atmospheric energy transport variability associated with decadal sea surface temperature variability in the tropical Pacific is studied using an atmospheric primitive equation model coupled to a slab mixed layer. The decadal variability is prescribed as an anomalous surface heat flux that represents the reduced ocean heat transport in the tropical Pacific when it is anomalously warm. The atmospheric energy transport increases and compensates for the reduced ocean heat transport. Increased transport by the mean meridional overturning (i.e., the strengthening of the Hadley cells) causes increased poleward energy transport. The subtropical jets increase in strength and shift equatorward, and in the midlatitudes the transients are affected. NCEP–NCAR reanalysis data show that the warming of the tropical Pacific in the 1980s compared to the early 1970s seems to have caused very similar changes in atmospheric energy transport indicating that these atmospheric transport variations were driven from the tropical Pacific. To study the implication of these changes for the coupled climate system an ocean model is driven with winds obtained from the atmosphere model. The poleward ocean heat transport increased when simulated wind anomalies associated with decadal tropical Pacific variability were used, showing a negative feedback between decadal variations in the mean meridional circulation in the atmosphere and in the Pacific Ocean. The Hadley cells and subtropical cells act to stabilize each other on the decadal time scale.
  • Support Vector Machines for Nonlinear State Space Reconstruction: Application to ...Asefa T., M. Kemblowski , U. Lall and G. Urroz | Water Resources Research , 2005 [+]
    Abstract: The reconstruction of low-order nonlinear dynamics from the time series of a state variable has been an active area of research in the last decade. The 154 year long, biweekly time series of the Great Salt Lake volume has been analyzed by many researchers from this perspective. In this study, we present the application of a powerful state space reconstruction methodology using the method of support vector machines (SVM) to this data set. SVM are machine learning systems that use a hypothesis space of linear functions in a kernel-induced higher-dimensional feature space. SVM are optimized by minimizing a bound on a generalized error (risk) measure rather than just the mean square error over a training set. Under Mercer’s conditions on the kernels the corresponding optimization problems are convex; hence global optimal solutions can be readily computed. The SVM-based reconstruction is used to develop time series forecasts for multiple lead times ranging from 2 weeks to several months. Unlike previously reported methodologies, SVM are able to extract the dynamics using only a few past observed data points out of the training examples. The reliability of the algorithm in learning and forecasting the dynamics is tested using split sample sensitivity analysis, with a particular interest in forecasting extreme states. Efforts are also made to assess variations in predictability as a function of initial conditions and as a function of the degree of extrapolation from the state space used for learning the model.
  • Why ocean heat transport warms the global mean climateHerweijer, C., R. Seager, M. Winton, and A. Clement | Tellus, 2005 [+]
    Abstract: Observational and modelling evidence suggest that poleward ocean heat transport (OHT) can vary in response to both natural climate variability and greenhouse warming. Recent modelling studies have shown that increased OHT warms both the tropical and global mean climates. Using two different coupled climate models with mixed-layer oceans, with and without OHT, along with a coupled model with a fixed-current ocean component in which the currents are uniformly reduced and increased by 50%, an attempt is made to explain why this may happen. OHT warms the global mean climate by 1 to 1.6 K in the atmospheric general circulation (AGCM) ML model and 3.5 K in the AGCM fixed current model. In each model the warming is attributed to an increase in atmospheric greenhouse trapping, primarily clear-sky greenhouse trapping, and a reduction in albedo. This occurs as OHT moistens the atmosphere, particularly at subtropical latitudes. This is not purely a thermodynamic response to the reduction in planetary albedo at these latitudes. It is a change in atmospheric circulation that both redistributes the water vapour and allows for a global atmospheric moistening—a positive ‘dynamical’ water vapour feedback. With increasing OHT the atmospheric water vapour content increases as atmospheric convection spreads out of the deep tropics. The global mean planetary albedo is decreased with increased OHT. This change is explained by a decrease in subtropical and mid-latitude low cloudiness, along with a reduction in high-latitude surface albedo due to decreased sea ice. The climate models with the mixed layer oceans underestimate both the subtropical low cloud cover and the high-latitude sea ice/surface albedo, and consequently have a smaller warming response to OHT.
  • Volcanic and Solar Forcing of the Tropical Pacific over the Past 1000 YearsMichael E. Mann, Mark A. Cane, Stephen E. Zebiak, and Amy Clement | Journal of Climate, 2005 [+]
    Abstract: The response of El Niño to natural radiative forcing changes over the past 1000 yr is investigated based on numerical experiments employing the Zebiak–Cane model of the tropical Pacific coupled ocean– atmosphere system. Previously published empirical results demonstrating a statistically significant tendency toward El Niño conditions in response to past volcanic radiative forcing are reproduced in the model experiments. A combination of responses to past changes in volcanic and solar radiative forcing closely reproduces changes in the mean state and interannual variability in El Niño in past centuries recorded from fossil corals. The dynamics of El Niño thus appear to have played an important role in the response of the global climate to past changes in radiative forcing.
  • Greedy algae reduce arsenateFerdi L. Hellweger, Kevin J. Farley, Upmanu Lall, Dominic M. Di Toro | American Society of Limnology and Oceanography, 2004 [+]
    Abstract: Algae reduce and methylate arsenate, producing arsenite (As(III)) when the growth rates are high and dimethylarsinic acid (DMA) when the growth rates are low. In lakes, this leads to high As(III) concentrations in the early stages of spring and fall blooms and high DMA concentrations in the summer. We hypothesize that under phosphorus (P)-limited conditions, which usually exist in the summer, algae take up phosphate (PO,) and, because of similar chemical characteristics, As(V) as well. Inside the cell, As(V) is reduced to As(III), methylated to monomethylar- sonic acid (MMA) and DMA, and then excreted. However, under non-P-limited conditions, which exist in the early stages of blooms, algae up-regulate their PO, transport system to take up excess P, a phenomenon known as luxury uptake. Since As(V) is taken up by the PO4 transport system, As(V) uptake also increases at this time. Within the cell, the reduction of As(V) to As(III) is fast, but methylation is slower, causing As(III) to build up in the cell and be excreted, which, in turn, causes an increase in extracellular As(III). This mechanism permits the synergistic (luxury uptake) and antagonistic (competition) effects of P04 on As(V) uptake and can therefore explain the seem- ingly contradictory results found in the literature. A mathematical model is constructed on the basis of existing established algal-nutrient interaction models and is used to simulate As transformation in two laboratory batch experiments. In addition to algal and P responses, the model can reasonably well reproduce the observed As(III) peak during the log growth phase and the more gradual appearance of DMA during the stationary phase.
  • Institutional Boundaries and Common-Pool Resource Management: A Comparative Analysis of Water ...Tanya Heikkila | Journal of Policy Analysis and Management, 2004 [+]
    Abstract: Policymakers and academics often identify institutional boundaries as one of the factors that shape the capacity of jurisdictions to manage natural resources such as water, forests, and scenic lands. This article examines two key bodies of literature—common-pool resource management theory and local public economy theory—to explain how the boundaries of political jurisdictions affect natural resource management. Two empirical methods were used to test hypotheses from the literature, using a study of water management programs in California. The results demonstrate that institutional boundaries that coincide with natural resources are likely to be associated with the implementation of more effective resource management programs. At the same time, where jurisdictions can control through coordination, they can also facilitate more effective resource management where jurisdictions do not match resource boundaries.
  • Sensitivity of atmospheric response to modeled snow anomaly characteristicsGavin Gong, Dara Entekhabi, Judah Cohen, and David Robinson | Journal of Geophysical Research, 2004 [+]
    Abstract: The presence of snow over broad land surface regions has been shown to not only suppress local surface temperatures, but also influence various remote climate phenomena. However, the specific mechanisms and snow anomaly characteristics which produce this response are still not well understood. In this study, large-ensemble general circulation model (GCM) experiments are performed to investigate the sensitivity of the atmospheric response to snow cover vs. snow depth anomalies, and the relevant surface thermodynamic processes involved. Realistic, observation-based, autumn-winter snow forcings over Siberia are developed and applied as model boundary conditions, to evaluate the climate response to (1) comprehensive snow forcings including snow cover and snow depth components, (2) snow cover only forcings, and (3) snow forcings in the absence of a surface albedo response. Results indicate that snow cover extent anomalies are not the only significant contributor to the local temperature response; snow depth anomalies are shown to have a comparable effect. Furthermore, the albedo effect is not the predominant thermodynamic mechanism; processes related to the insulative properties of the snowpack (e.g., thermal conductivity and latent heat flux) are also involved. Lastly, we find that realistic snow cover and snow depth anomalies acting in conjunction are required to produce a local temperature response which is strong enough to distinctly modulate the winter Arctic Oscillation (AO) mode as shown in previous studies. Such a detailed understanding of the atmospheric sensitivity to snow anomaly characteristics is beneficial for effectively utilizing any potential climate predictability contained in snow anomaly signals.
  • Orographic Constraints on a Modeled Siberian Snow-Tropospheric-Stratospheric Teleconnection PathwayGavin Gong, Dara Entekhabi, and Judah Cohen | Journal of Climate, 2004 [+]
    Abstract: Previous modeling studies have identified a teleconnection pathway linking observation-based early season Siberian snow perturbations to a modulation of the winter Arctic Oscillation (AO) mode. In this study, the key role of orography in producing this modeled teleconnection is explicitly investigated using numerical experiments analogous to the previous studies. The climatic response to the same snow perturbation is investigated under modied orographic barriers in southern and eastern Siberia. Reducing these barriers results in a weakening of the prevailing orographically forced region of stationary wave activity centered over Siberia, as well as the snow-forced upward wave flux anomaly that initiates the teleconnection. This diminished anomaly propagates upward, but does not extend into the stratosphere to weaken the polar vortex. Consequently, poleward refraction of upper-tropospheric waves and downward propagation of coupled wave–mean flow anomalies, which ultimately produce the negative winter AO response, fail to develop. Thus, the mountains represent an orographic constraint on the snow–AO teleconnection pathway. By reducing the orographic barrier, the snow-forced influx of wave energy remains in the troposphere and, instead, produces a hemispheric-scale equatorward wave refraction.
  • Predictability of El Niño over the past 148 yearsDake Chen, Mark A. Cane, Alexey Kaplan, Stephen E. Zebiak, and Daji Huang | Nature, 2004 [+]
    Abstract: Forecasts of El Nin˜o climate events are routinely provided and distributed, but the limits of El Nin˜o predictability are still the subject of debate. Some recent studies suggest that the predictability is largely limited by the effects of high-frequency atmospheric ‘noise’ (1–7), whereas others emphasize limitations arising from the growth of initial errors in model simulations (8–10). Here we present retrospective forecasts of the interannual climate fluctuations in the tropical Pacific Ocean for the period 1857 to 2003, using a coupled ocean–atmosphere model. The model successfully predicts all prominent El Nin˜o events within this period at lead times of up to two years. Our analysis suggests that the evolution of El Nin˜o is controlled to a larger degree by self-sustaining internal dynamics than by stochastic forcing. Model-based prediction of El Nin˜o therefore depends more on the initial conditions than on unpredictable atmospheric noise. We conclude that throughout the past century, El Nin˜o has been more predictable than previously envisaged.
  • Predictability of Tropical Pacific Decadal Variability in an Intermediate ModelAlicia R. Karspeck, Richard Seager, and Mark A. Cane | Journal of Climate, 2004 [+]
    Abstract: The Zebiak–Cane (ZC) model for simulation of the El Nin˜o–Southern Oscillation is shown to be capable of producing sequences of variability that exhibit shifts in the time-mean state of the eastern equatorial Paci?c that resemble observations of tropical Paci?c decadal variability. The model’s performance in predicting these shifts is compared to two naive forecasting strategies. It is found that the ZC model consistently outperforms the two naive forecasts that serve as a null hypothesis in assessing the significance of results. Forecasts initialized during anomalously warm and anomalously cold decades are shown to have the highest predictability. These modeling results suggest that, to a moderate extent, the state of the tropical Pacific in one decade can predetermine its time-mean state in the following decade. However, even in this idealized context decadal forecasting skill is modest. Results are discussed in the context of their implications for the ongoing debate over the origin of decadal variations in the Pacific.
  • Land-use choices: balancing humans needs and ecosystem functionRuth S. DeFries, Jonathan A. Foley, and Gregory P. Asner | The Ecological Society of America, 2004 [+]
    Abstract: Conversion of land to grow crops, raise animals, obtain timber, and build cities is one of the foundations of human civilization. While land use provides these essential ecosystem goods, it alters a range of other ecosystem functions, such as the provisioning of freshwater, regulation of climate and biogeochemical cycles, and maintenance of soil fertility. It also alters habitat for biological diversity. Balancing the inherent trade-offs between satisfying immediate human needs and maintaining other ecosystem functions requires quantitative knowledge about ecosystem responses to land use. These responses vary according to the type of land-use change and the ecological setting, and have local, short-term as well as global, long-term effects. Land-use decisions ultimately weigh the need to satisfy human demands and the unintended ecosystem responses based on societal values, but ecological knowledge can provide a basis for assessing the trade-offs.
  • How Can Tropical Pacific Ocean Heat Transport Vary?Wilco Hazeleger, Richard Seager, Mark A. Cane, and Naomi H. Naik | Journal of Physical Oceanography, 2004 [+]
    Abstract: Pacific Ocean oceanic heat transport is studied in an ocean model coupled to an atmospheric mixed-layer model. The shallow meridional overturning circulation cells in the Tropics and subtropics transport heat away from the equator. The heat transport by the horizontal gyre circulation in the Tropics is smaller and directed toward the equator. The response of the Pacific oceanic heat transport to El Nin˜o–like winds, extratropical winds, and variations in the Indonesian Throughflow is studied. Large, opposing changes are found in the heat transport by the meridional overturning and the horizontal gyres in response to El Nin˜o–like winds. Consequently, the change in total heat transport is relatively small. The overturning transport decreases and the gyres spin down when the winds decrease in the Tropics. This compensation breaks down when the Indonesian Through?ow is allowed to vary in the model. A reduced Indonesian Throughflow, as observed during El Nin˜ o–like conditions, causes a large reduction of poleward heat transport in the South Pacific and affects the ocean heat transport in the southern tropical Paci?c. Extratropical atmospheric anomalies can affect tropical ocean heat transport as the tropical thermocline is ventilated from the extratropics. The authors find that changes in the heat loss in the midlatitudes affect tropical ocean heat transport by driving an enhanced buoyancy-driven overturning that reaches into the Tropics. The results are related to observed changes in the overturning circulation in the Pacific in the 1990s, sea surface temperarture changes, and changes in atmospheric circulation. The results imply that the ratio of heat transport in the ocean to that in the atmosphere can change.
  • Predicting Pacific Decadal VariabilityR. Seager, A. R. Karspeck, M. A. Cane, Y. Kushnir, A. Giannini, A. Kaplan, B. Kerman, and J. Velez | American Geophysical Union, 2004 [+]
    Abstract: The case is advanced that decadal variability of climate in the Pacific sector is driven by tropical atmosphere-ocean interactions and communicated to the extratropics. It is shown that tropical decadal variations in the last century could arise as a conse­ quence of the regional subset of physics contained within an intermediate model of the El Nino-Southern Oscillation. These decadal changes in ENSO and tropical mean climate are more predictable than chance years in advance but even in these idealized experiments forecast skill is probably too small to be useful. Nonethe­ less, forecasts of the next two decades indicate that, according to this model, the 1998 El Nino marked the end of the post 1976 tropical Pacific warm period. Observations and atmosphere general circulation models are interpreted to sug­ gest that decadal variations of the atmosphere circulation over the North Pacific between the 1960s and the 1980s are explained by a mix of tropical forcing and internal atmospheric variability. This places a limit on their predictability. The ocean response to extratropical atmosphere variability consists of a local response that is instantaneous and a delayed response of the subtropical and subpolar gyres that is predictable a few years in advance. It is shown that the wintertime internal variability of the Aleutian Low can weakly impact the ENSO system but its impact on decadal predictability is barely discernible.
  • Small-scale variability and model error in tropical Pacific sea levelA. Kaplan, M. A. Cane, D. Chen, D. L. Witter, and R. E. Cheney | Journal of Geophysical Research , 2004 [+]
    Abstract: Monthly interannual anomalies of tropical Pacific sea level height from TOPEX/ Poseidon altimetry are compared with simulation and assimilation products from a variety of models, ranging from a simple linear long wave approximation to ocean general circulation models. Major spatial similarities in the error patterns are identified. These include zonally elongated maxima in the northwest and southwest tropical Pacific Ocean, a band of high values near 10N, slightly inclined toward the equator from the Central American coast, and low values on the equator and in the southeastern tropical Pacific. These features are also present in the pattern of small-scale variability (SSV) of sea level height. Spatial and temporal components of this SSV are analyzed for predominant variability types. Monte Carlo experiments identify the areas where high SSV is wind driven, caused by a similar pattern of variability in the wind stress. Model products systematically underestimate signal variance in such areas. Variability in other areas is due to the instability of ocean currents. The major component of uncertainty in the gridded satellite altimeter analyses is due to sampling error, for which estimates are developed and verified.
  • May 2003 Disaster in Sri Lanka and Cyclone 01-B in the Bay of BengalLareef Zubair | Natural Hazards, 2004 [+]
    Abstract: Heavy rainfall deluged South-Western Sri Lanka between the 11th and 19th of May 2003 and led to its worst disaster in 50 years. Floods and landslides claimed 260 lives. The World Meteorological Organization cited it as evidence for the increase of anomalous climatic extremes in recent years. Here, a meteorological analysis is presented of this disaster as part of a sustained effort to undertake meteorological applications for disaster management. There were intense lowlevel westerlies over Sri Lanka related to cyclone 01-B that made its way across the Bay of Bengal at least 700 km away. The southeastwardly traverse of the cyclone was stalled for a few days by anomalous north-westerly geostrophic winds over South Asia. Here, it is argued that orographic rainfall induced by this stalled cyclone and seasonal inter-tropical convergence zone cloud bands over Sri Lanka led to the deluge. The trajectory of the cyclone was remote from Sri Lanka and this led to no cyclone hazard warnings being issued. No cyclones have made landfall in Sri Lanka in May in the last 100 years. This study shows that one must exercise vigilance not only in the path of the cyclone but also remotely due to the modulation of the cyclone by other atmospheric phenomenon and topographic features. This flood may have been predicted with contemporary local area weather prediction models and this example points to the need for the development of local area weather prediction models as part of disaster warning systems. This study also demonstrates the use of meteorological diagnostics for post-event analysis of hydrometeorology of disaster events.
  • Flood quantiles in a changing climate: Seasonal forecasts and causal relationsA. Sankarasubramanian and Upmanu Lall | Water Resources Research, 2003 [+]
    Abstract: Recognizing that the frequency distribution of annual maximum floods at a given location may change over time in response to interannual and longer climate fluctuations, we compare two approaches for the estimation of flood quantiles conditional on selected ‘‘climate indices’’ that carry the signal of structured low-frequency climate variation, and influence the atmospheric mechanisms that modify local precipitation and flood potential. A parametric quantile regression approach and a semiparametric local likelihood approach are compared using synthetic data sets and for data from a streamflow gauging station in the western United States. Their relative utility in different settings for seasonal flood risk forecasting as well as for the assessment of long-term variation in flood potential is discussed.
  • Relative impacts of Siberian and North American snow anomalies on the winter Arctic OscillationGavin Gong, Dara Entekhabi, and Judah Cohen | Geophysical Research Letters, 2003 [+]
    Abstract: Numerical model mean climatic response to realistic land surface snow forcings is evaluated for two different forcing regions, Siberia and North America. The atmospheric teleconnection pathway and negative winter AO mode response produced by the Siberia forcing, described by the authors in previous studies, is not produced by the comparable-extent North America forcing. It is shown that the combination of a large snow-forced local diabatic heating anomaly over a region of substantial stationary wave activity is required to produce strong upward wave activity flux anomalies which initiate the teleconnection pathway. These features are unique to Siberia, making it a critical region for reproducing the snow - winter AO statistical relationship evident in the observational record.
  • What led to the May 2003 Floods?Lareef Zubair, Upamala Tennakone, Zeenas Yahiya, Janaki Chandimala and M.R.A. Siraj | Engineer, 2003 [+]
    Abstract: Heavy Rainfall deluged the South-western corner of Sri Lanka between the 11th and 19th of May 2003. Floods and landslides claimed 260 lives. Schools, homes, and other infrastructure were destroyed. It was the worst disaster in 50 years. The heaviest rainfall for May 2003 of 899 mm was recorded at Gonapenigala Iranganie Estate and the third heaviest rainfall of 755 mm was recorded at Panilkande Estate. The monthly rainfall in Ratnapura was 718 mm and this is a station with reliable data. This shows that the rainfall was not as high as past extreme events at a monthly scale. however half of the monthly rainfall fell on the 17th of May and indeed, the rainfall was highly concentrated to the South-west of Ratnapura.
  • Reduced Space Approach to the Optimal Analysis of Historical Marine Observations: Accomplishments...A. Kaplan, M. A. Cane, and Y. Kushnir | World Meteorological Organization, 2003 [+]
    Abstract: Observed historical climate fields are characterized by comparatively precise data and good coverage in the last few decades, and by poor observational coverage prior to then. The technique of the reduced space optimal analysis of such fields (i.e. estimating them in projections onto a low-dimensional space spanned by the leading patterns of the signal variability) is presented in the context of more traditional approaches to data analysis. Advantages of the method are illustrated on examples of reconstructions of near-global monthly fields of sea surface temperature and sea level pressure from the 1850s to the present, along with verified error bars. The limitations of the technique as regards quality and robustness of estimating a priori parameters, representation of long-term and small-scale types of variability, assumption of stationarity of means and covariances, and incompleteness of coverage are discussed, and possible ways to overcome these problems are suggested.
  • El Niño-Southern Oscillation Influences on the Mahaweli Streamflow in Sri LankaLareef Zubair | International Journal of Climatology, 2003 [+]
    Abstract: Despite advances over the last two decades in the capacity to predict the evolution of the El Nino–southern oscillation ˜ (ENSO) phenomenon and advances in understanding of the relationship between ENSO and climate, there has been little use of climate predictions for water resources management in the tropics. As part of an effort to develop such a prediction scheme, the ENSO influences on streamflow and rainfall in the upper catchment of the Mahaweli river in Sri Lanka were investigated with correlation analysis, composite analysis and contingency tables. El Nino conditions were ˜ often associated with decreased annual flows and La Nina with increased flows. The relationship of streamflow and rainfall ˜ with the ENSO index of NINO3 contrasted between January to September and October to December. During El Nino˜ episodes the streamflow declines from January to September, but from October to December there is no clear relationship. On the other hand, rainfall shows a clear increase from October to December and declines during January, February, March, July and August. The simultaneous correlations of NINO3 with the aggregate January to September streamflow (r = 0.50), with January to September rainfall (r = 0.44) and with October to December rainfall (r = 0.48) are all significant at the 99% level. The correlation between one-season-in-advance NINO3 with both January to September streamflow and October to December rainfall remained significant at the 99% level. This study demonstrates the potential of using ENSO-based predictors for a seasonal hydro-climatic prediction scheme in the Mahaweli basin. It shows the signi?cant contrasts in ENSO influence on rainfall and streamflow due to various hydrological processes. It has demonstrated that the potential for prediction is improved by investigating ENSO influences for the appropriate season for the given river catchment.
  • Modeled Northern Hemisphere Winter Climate Response to Realistic Siberian Snow AnomaliesGavin Gong, Dara Entekhabi, and Judah Cohen | Journal of Climate, 2003 [+]
    Abstract: Wintertime Northern Hemisphere climate variability is investigated using large-ensemble (20) numerical GCM simulations. Control simulations with climatological surface (land and ocean) conditions indicate that the Arctic Oscillation (AO) is an internal mode of the Northern Hemisphere atmosphere, and that it can be triggered through a myriad of perturbations. In this study the role of autumn land surface snow conditions is investigated. Satellite observations of historical autumn–winter snow cover are applied over Siberia as model boundary conditions for two snow-forced experiments, one using the highest observed autumn snow cover extent over Siberia (1976) and another using the lowest extent (1988). The ensemble-mean difference between the two snow-forced experiments is computed to evaluate the climatic response to Siberian snow conditions. Experiment results suggest that Siberian snow conditions exert a modulating influence on the predominant wintertime Northern Hemisphere (AO) mode. Furthermore, an atmospheric teleconnection pathway is identi?ed, involving well-known wave– mean flow interaction processes throughout the troposphere and stratosphere. Anomalously high Siberian snow increases local upward stationary wave flux activity, weakens the stratospheric polar vortex, and causes upper troposphere stationary waves to refract poleward. These related stationary wave and mean flow anomalies propagate down through the troposphere via a positive feedback, which results in a downward-propagating negative AO anomaly during the winter season from the stratosphere to the surface. This pathway provides a physical explanation for how regional land surface snow anomalies can influence winter climate on a hemispheric scale. The results of this study may potentially lead to improved predictions of the winter AO mode, based on Siberian snow conditions during the preceding autumn.
  • Sustainable Groundwater Management Problems and Scientific ToolsKinzelbach W., Bauer P., Siegfried T. And Brunner P | Episodes , 2003 [+]
    Abstract: Groundwater is a strategic resource due to its usually high quality and perennial availability. However, groundwater management all over the world often lacks sustainability as evidenced by falling water tables, drying wetlands, increasing sea-water intrusion and general deterioration of water quality, As groundwater cannot be renewed artificially on a large scale, sustainable management of this resource is vital. A number of scientific tools are available to assist in his task. Three items are discussed here. They include methods for the determination of groundwater recharge, groundwater modeling including the estimation of its uncertainty, and the interfacing to the socio-economic field. Generally the quality of water management work can be largely enhanced with new tools available, including remote sensing, digital terrain models, differential GPS, environmental tracers, automatic data collection, modeling and the coupling of models from different disciplines.
  • Validation of a watershed model without calibrationRichard M. Vogel and A. Sankarasubramanian | Water Resources Research, 2003 [+]
    Abstract: Traditional approaches for the validation of watershed models focus on the ‘‘goodness of fit’’ between model predictions and observations. It is possible for a watershed model to exhibit a ‘‘good’’ fit, yet not accurately represent hydrologic processes; hence ‘‘goodness of fit’’ can be misleading. Instead, we introduce an approach which evaluates the ability of a model to represent the observed covariance structure of the input (climate) and output (streamflow) without ever calibrating the model. An advantage of this approach is that it is not confounded by model error introduced during the calibration process. We illustrate that once a watershed model is calibrated, the unavoidable model error can cloud our ability to validate (or invalidate) the model. We emphasize that model hypothesis testing (validation) should be performed prior to, and independent of, parameter estimation (calibration), contrary to traditional practice in which watershed models are usually validated after calibrating the model. Our approach is tested using two different watershed models at a number of different watersheds in the United States.
  • Mechanisms of Hemispherically Symmetric Climate VariabilityRichard Seager, Nili Harnik, Yochanan Kushnir, Walter Robinson, and Jennifer Miller | Journal of Climate, 2003 [+]
    Abstract: Inspired by paleoclimate evidence that much past climate change has been symmetric about the equator, the causes of hemispherically symmetric variability in the recent observational record are examined using the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset and numerical models. It was found that the dominant cause of hemispherically symmetric variability is the El Nin˜o–Southern Oscillation. During an El Nin˜ o event the Tropics warm at all longitudes and the subtropical jets in both hemispheres strengthen on their equatorward flanks. Poleward of the tropical warming there are latitude belts of marked cooling, extending from the surface to the tropopause in both hemispheres, at all longitudes and in all seasons. The midlatitude cooling is caused by changes in the eddy-driven mean meridional circulation. Changes in the transient eddy momentum fluxes during an El Nin˜o event force upper-tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the Coriolis torque. The eddy-driven ascent causes anomalous adiabatic cooling, which is primarily balanced by anomalous diabatic heating. Using a quasigeostrophic spherical model, forced by an imposed surface eddy disturbance of chosen wavenumber and frequency, it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude–height plane of transient eddies. Changes in zonal winds, and associated changes in the meridional gradient of potential vorticity, create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward. Tropical forcing of variability in the eddy-driven mean meridional circulation is another way, in addition to Rossby wave teleconnections, whereby the Tropics can in?uence extratropical climate. Unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle.
  • Sensitivity of Kelani streamflow in Sri Lanka to ENSOLareef Zubair | Hydrological Processes, 2003 [+]
    Abstract: As part of an effort to demonstrate the use of climate predictions for water resources management, the El Nino/Southern ˜ Oscillation (ENSO) influences on stream flow in the Kelani River in Sri Lanka were investigated using correlation analysis, composite analysis and contingency tables. El Nino (warm phase of ENSO) was associated with decreased ˜ annual stream flow and La Nina (cold phase of ENSO) with increased annual flows. The annual stream flow had ˜ a negative correlation with the simultaneous ENSO index of NINO3Ð4 that was significant at the 95% level. This negative correlation is enhanced to a 99% level if the aggregate January to September or the April to September stream flow alone were considered. Although, there is little correlation between ENSO indices and stream flow during the October to December period, there is a high correlation between rainfall and NINO3Ð4 (r D 0Ð51, significant at the 99% level). Therefore ENSO based rainfall predictions can be used along with a hydrological model to predict the October to December stream flow. This study demonstrates the viability of using ENSO based predictors for January to September or April to September stream flow predictions in the Kelani River. The October to December stream ?ow may be predicted by exploiting the strong relationship between ENSO and rainfall during that period.
  • Effect of persistence on trend detection via regressionNicholas C. Matalas and A. Sankarasubramanian | Water Resources Research, 2003 [+]
    Abstract: Trends in hydrologic sequences may be assessed in various ways. The coefficient of regression of flow on time may be used, particularly if the sequences are very long. Under the assumption of stationarity the variance of the regression coefficient is expressed as a function of sequence length and the autocorrelation coefficients of relevant order. Thus the variance inflation factor for assessing the statistical significance of estimated regression coefficients may be readily determined for any given stationary process. The variance inflation factor is determined for four stationary processes: independent, Markov, autoregressive-moving average of order (1, 1), and fractional Gaussian noise. The effectiveness of prewhitening observed sequences with a Markov process is nearly the same whether the first order autocorrelation coefficient is known per se or through estimation.
  • Hydroclimatology of the continental United StatesA. Sankarasubramanian and Richard M. Vogel | Geophysical Research Letters, 2003 [+]
    Abstract: The overall water balance and the sensitivity of watershed runoff to changes in climate are investigated using national databases of climate and streamflow for 1,337 watersheds in the U.S. We document that 1% changes in precipitation result in 1.5– 2.5% changes in watershed runoff, depending upon the degree of buffering by storage processes and other factors. Unlike previous research, our approach to estimating climate sensitivity of streamflow is nonparametric and does not depend on a hydrologic model. The upper bound for precipitation elasticity of streamflow is shown to be the inverse of the runoff ratio. For over a century, investigators [Pike, 1964; Budyko, 1974; Ol’dekop, 1911; and Schreiber, 1904] have suggested that variations in watershed aridity alone are sufficient to predict spatial variations in long-term watershed runoff. We document that variations in soil moisture holding capacity are just as important as variations in watershed aridity in explaining the mean and variance of annual watershed runoff.
  • Modulation of Sri Lankan Maha rainfall by the Indian Ocean DipoleLareef Zubair, Suryachandra A. Rao, and Toshio Yamagata | Geophysical Research Letters, 2003 [+]
    Abstract: Investigating the September to December rainy season in Sri Lanka associated with the Maha rice growing season provides insights into the Asian monsoon during the boreal fall. Here, the modulation of the Maha rainfall by the tropical air_sea coupled phenomenon referred to as the Indian Ocean Dipole (IOD) is documented. The Maha rainfall has a strong and robust association with the IOD from 1869 to 2000. The anomalously warm sea surface in the western Indian Ocean associated with the positive IOD phase induces large scale convergence in the lower troposphere extending to Sri Lanka leading to the preponderant enhancement of Maha rainfall.
  • A Large-Ensemble Model Study of the Wintertime AO-NAO and the Role of Interannual Snow PerturbationsGavin Gong, Dara Entekhabi, and Judah Cohen | Journal of Climate, 2002 [+]
    Abstract: Numerous studies have hypothesized that surface boundary conditions or other external mechanisms drive the hemispheric mode of atmospheric variability known as the Arctic Oscillation (AO), or its regional counterpart, the North Atlantic Oscillation (NAO). However, no single external factor has emerged as the dominant forcing mechanism, which has led, in part, to the characterization of the AO–NAO as a fundamental internal mode of the atmospheric system. Nevertheless, surface forcings may play a considerable role in modulating, if not driving, the AO–NAO mode. In this study, a pair of large-ensemble atmospheric GCM experiments (with SST climatology), one with prescribed climatological snow mass and another with freely varying snow mass, is conducted to investigate the degree to which the AO–NAO is modulated by interannual variability of surface snow conditions. Statistical analysis of the results indicates that snow anomalies are not required to produce the AO– NAO mode of variability. Nevertheless, interannual variations in snow mass are found to exert a modulating in?uence on the AO–NAO mode. Snow variations excite the AO pattern over the North Atlantic sector, produce correlated hemispheric AO features throughout the troposphere and stratosphere, and generate autumn sea level pressure anomalies over Siberia that evolve into the winter AO–NAO. These numerical modeling results are consistent with previous observational analyses that statistically link the AO–NAO mode with the Siberian high and associated snow cover variations.
  • Using a Dynamic Hydrology Model To Predict Mosquito Abundances in Flood and Swamp WaterJeffrey Shaman, Marc Stieglitz, Colin Stark, Sylvie Le Blancq, and Mark Cane | Emerging Infectious Diseases, 2002 [+]
    Abstract: We modeled surface wetness at high resolution, using a dynamic hydrology model, to predict flood and swamp water mosquito abundances. Historical meteorologic data, as well as topographic, soil, and vegetation data, were used to model surface wetness and identify potential fresh and swamp water breeding habitats in two northern New Jersey watersheds. Surface wetness was positively associated with the subsequent abundance of the dominant floodwater mosquito species, Aedes vexans, and the swamp water species, Anopheles walkeri. The subsequent abundance of Culex pipiens, a species that breeds in polluted, eutrophic waters, was negatively correlated with local modeled surface wetness. These associations permit real-time monitoring and forecasting of these floodwater and nonfloodwater species at high spatial and temporal resolution. These predictions will enable public health agencies to institute control measures before the mosquitoes emerge as adults, when their role as transmitters of disease comes into play.
  • Comment on the paper: Basin hydrologic response relations to distributed physiographic ...A. Sankarasubramanian and Richard M. Vogel | Journal of Hydrology, 2002 [+]
    Abstract: A basic problem relating to the long-term water balance involves splitting precipitation P, into runoff R, and actual evapotranspiration E. Berger and Entekhabi (2001) showed that the evapotranspiration efficiency E/Ep (Ep denotes potential evapotranspiration) and the runoff ratio R/P, are related to physiographic basin features and regional climate information. Berger and Entekhabi (2001) estimated actual watershed evapotranspiration E, and runoff R, at 10 basins across the US, using an equilibrium distributed hydrologic model. They argue that their results are preliminary because they are only based on modeled values of E and R. They suggest that the next step is to assemble observed evapotranspiration and runoff data for a number of basins to test their modeled results. We describe the results of such experiments here. We develop basin hydrologic response relations using observed (instead of modeled) fluxes of runoff from 1305 basins in the continental US. Analogous to their study which employed six basin descriptors, this study uses the following four basin characteristics: wetness ratio P/Ep, relative infiltration capacity ir/Ks, average slope S, and drainage density Dd. A linear regression model is developed which relates the runoff ratio to those basin descriptors, and our model is compared with an analogous model developed by Berger and Entekhabi.
  • Tropical Pacific 1976-77 Climate Shift in a Linear, Wind-Driven ModelAlicia R. Karspeck and Mark A. Cane | Journal of Physical Oceanography , 2002 [+]
    Abstract: A number of studies have attempted to explain the cause of decadal variability in the tropical Paci?c and explore its possible link to decadal variability in the midlatitude Pacific. To investigate some of the current theories of Pacific decadal variability, a linear, wind-driven model, designed to simulate only baroclinic wave dynamics, was forced with wind stress anomalies in the Pacific Ocean basin from 1945 through 1992. An analysis technique designed to isolate the decadal/interdecadal scale variability from interannual ENSO variability was performed on the model’s thermocline depth anomaly (TDA). It was found that the temporal and spatial patterns of the observed tropical decadal sea surface temperatures are consistent with our modeled TDA. Furthermore, restricting the wind forcing to within 58 of the equator does not substantially alter the decadal/interdecadal variability of the equatorial region. The authors conclude that the observed decadal variability in the low-latitude Pacific is primarily a linear dynamical response to tropical wind forcing and does not directly require an oceanic link to the midlatitudes. The question of how tropical wind anomalies are generated is not addressed. In addition, it is shown that in model scenarios where the wind forcing is restricted to the western equatorial Pacific, the 1976–77 climate shift is still clearly visible as a dominant feature of tropical decadal variability. The temporal decadal signal of the model-generated TDA is more pronounced during the eastern equatorial upwelling season (July–September) than in the boreal winter. This is consistent with the observed seasonal bias in tracer and SST data from the eastern equatorial Pacific.
  • A simple coupled model of tropical Atlantic decadal climate variabilityYochanan Kushnir, Richard Seager, and Jennifer Miller | Geophysical Research Letters, 2002 [+]
    Abstract: A linear, zonally averaged model of the interaction between the tropical Atlantic (TA) atmosphere and ocean is presented. A balance between evaporation and meridional heat advection in the mixed layer determines the sea surface temperature tendency. The atmosphere is a fixeddepth, sub-cloud layer in which the specific humidity anomaly is determined by a steady-state balance between evaporation, meridional advection, and a parameterized humidity exchange with the free atmosphere. When the model is integrated, forced with observed surface wind anomalies from 1965 to the present, its simulation of the observed sea surface temperature (SST) is realistic and comparable to a simulation with a full ocean GCM. A statistical representation of surface winds and their relationship to the SST gradient across the equator is used to formulate and test a coupled model of their regional variability. Forced on both sides of the equator, in the tradewind regions, with ‘‘white-noise’’ windspeed perturbations, the SST-wind relationship in the near-equatorial region feeds back positively on existing SST anomalies and gives rise to decadal variability.
  • Development of Meteorology in Sri LankaLareef Zubair | Journal of the Institution of Engineers, 2002 [+]
    Abstract: The fields of meteorology, oceanography and climatology have begun to receive renewed interest globally on account of environmental awareness and concern regarding climate change, the El Nino phenomena and hydrological and weather anomalies. Weather and Climate bears on critical fields such as energy, irrigation, public health, infrastructure planning, construction, fisheries, wildlife, vegetation and agriculture. Thus improvements in the fields of meteorology and climatology should be understood, supported and harnessed by professionals in the many sectors concerned with the environment of Sri Lanka. Here, the history of meteorology in Sri Lanka is reviewed, along with a summary of communication among meteorologists, state of the literature and its availability in Sri Lanka, education in meteorology and data availability. Finally, seven steps are proposed for the immediate development of meteorological and climate field in Sri Lanka.
  • Enhanced sensitivity of persistent events to weak forcing in dynamical and stochastic systems: ...Samar Khatiwala, Bruce E. Shaw, and Mark A. Cane | Geophysical Research Letters, 2001 [+]
    Abstract: Low-dimensional models can give insight into the climate system, in particular its response to externally imposed forcing such as the anthropogenic emission of greenhouse gases. Here, we use the Lorenz system, a chaotic dynamical system characterized by two \regimes", to examine the e ect of a weak imposed forcing. We show that the probability density functions (PDF's) of time-spent in the two regimes are exponential, and that the most dramatic response to forcing is a change in the frequency of occurrence of extremely persistent events, rather than the weaker change in the mean persistence time. This enhanced sensitivity of the \tails of the PDF's to forcing is quantitatively explained by changes in the stability of the regimes. We demonstrate similar behavior in a stochastically forced double well system. Our results suggest that the most significant e ect of anthropogenic forcing may be to change the frequency of occurrence of persistent climate events, such as droughts, rather than the mean.
  • Climate elasticity of streamflow in the United StatesA. Sankarasubramanian, Richard M. Vogel, and James F. Limbrunner | Water Resources Research, 2001 [+]
    Abstract: Precipitation elasticity of streamflow, «P , provides a measure of the sensitivity of stream?ow to changes in rainfall. Watershed model– based estimates of «P are shown to be highly sensitive to model structure and calibration error. A Monte Carlo experiment compares a nonparametric estimator of «P with various watershed model– based approaches. The nonparametric estimator is found to have low bias and is as robust as or more robust than alternate model-based approaches. The nonparametric estimator is used to construct a map of «P for the United States. Comparisons with 10 detailed climate change studies reveal that the contour map of «P introduced here provides a validation metric for past and future climate change investigations in the United States. Further investigations reveal that «P tends to be low for basins with significant snow accumulation and for basins whose moisture and energy inputs are seasonally in phase with one another. The Budyko hypothesis can only explain variations in «P for very humid basins.
  • Seasonality in the Impact of ENSO and the North American High on Caribbean RainfallA. Giannini, Y. Kushnir, and M. A. Cane | Physics and Chemistry of the Earth, 2001 [+]
    Abstract: Caribbean rainfall is affected by climate variability of Pacific and Atlantic origin, e.g. the El Nino-Southern Oscillation (ENSO) phenomenon, and variability in the North Atlantic High sea level pressure (SLP) center, respectively. During the lifetime of an ENS0 cycle, the basin experiences dry and wet extremes. In the case of a warm event, the dry extreme precedes the mature ENS0 phase, and can be explained in terms of a direct response to the atmospheric anomaly generated by the warm sea surface temperatures (SST) in the eastern equatorial Pacific. The wet extreme follows the mature phase, and is consistent with the lagged warming effect of ENS0 on tropical North Atlantic SSTs. The wintertime state of the North Atlantic High is hypothesized to affect Caribbean rainfall through its effect on tropical SST. A strong North Atlantic High SLP center during the early months of the calendar year strengthens the trade winds, hence cooling SSTs in the tropical latitudes of the North Atlantic. The effect lingers on most noticeably until the start of the Caribbean rainy season, in May-June, when cool SSTs are associated with deficient rainfall in the basin.
  • Institutions and Conjunctive Water Management among Three Western StatesBlomquist, W., T. Heikkila and E. Schlager | Natural Resources Journal, 2001 [+]
    Abstract: Conjunctive water management involves the coordinated use of ground and surface water supplies. It aims to enhance overall water supplies and guard against drought. In this article, we consider how water governance institutions affect the implementation of conjunctive management. To explain this connection, we present data from a study of conjunctive management in Arizona, California, and Colorado. We discuss how the institutional arrangements across these three states impact the transaction costs and other factors associated with conjunctive management and suggest how different institutional arrangements facilitate or impede conjunctive management.
  • Interdecadal changes in the ENSO teleconnection to the Caribbean region and the North Atlantic ...Alessandra Giannini, Mark A. Cane, and Yochanan Kushnir | Journal of Climate, 2001 [+]
    Abstract: The El Nino-Southern Oscillation (ENSO) phenomenon and variability in subtropical North Atlantic High sea level pressure (SLP) are known to a ect rainfall in the Caribbean region. An El Ni~no event i s as so ciated with drier than average conditions during the b ore al summer of year (0), and wetter than average conditions during the spr ing of year (+1). Dry conditions during the summer of year (0) of an El Ni~no are associate d with the locally divergent surface circulation engendered by the e astward shift of deep convection in the Paci c Ocean. Wet conditions during the spring of ye ar (+1) of an El Ni ~no are associate d with the lagged warming of the tropical North Atlantic Ocean. Variability in the strength of the North Atlantic High is governe d mainly by the North Atlantic Oscillation (NAO) with a p o s itive NAO phase implying a stronger than normal High and viceversa. The NAO i s negatively correlated with Caribbean rainfall, indirectly, via anomalous sea surface temperatures (SST) associate d with anomalies in the surface wind sp ee d at tropical latitude s, and directly, via anomalous sub s idence. The combined e ect of the two phenomena i s found to be strongest when the two signals interfere constructively: --during the summer following winters characterized by the p o s itive phase of the NAO, the dryness associate d with a developing warm ENSO event adds to the dryness associated with a p o s itive SLP anomaly in the subtropical North Atlantic (7 out of 11 El Ni ~nos between 1949 and 1999 fall in this category); -- during the spr ing following winters characterized by the negative phase of the NAO, the wetne s s that follows a warm ENSO event i s augmente d by the wetne s s as so ciated with the warmer than average tropical North Atlantic SSTs (5 out of 11 El Ni ~nos between 1949 and 1999 fall in this category). The coincidence in the recurrence of a positive phas e of the NAO during the winters coinciding with p e ak warm ENSO conditions has increased in the last 20 years compared to the previous few decade s. This partially explains the noticeable consistent dry signal over the Caribbean during the summer of year (0) of a warm ENSO event, and the disappearance of the wet signal during the spr ing of year (+1) in the recent record.
  • Challenges for environmental impact assessment in Sri LankaLareef Zubair | Environmental Impact Assessment Review, 2001 [+]
    Abstract: Salient features in the environmental impact assessment (EIA) process in Sri Lanka have proven to be the provision for public participation, the requirement of alternative proposals, and the use of a prescribed list to identify projects that must undergo review. While EIA has been successfully introduced and over 500 projects have been reviewed, some significant shortcomings remain. Integrated government policies on the types of projects that are encouraged in various zones are needed. Environmental data and effluent standards are insufficient. A code of conduct for project-approving authorities and the EIA consultants is needed. The infrastructure to monitor and enforce environmental regulations is inadequate. Addressing these shortcomings will be challenging given the opposition to the EIA process and the limitations in resources. But it is all the more important so that EIA can become entrenched in project appraisal.
  • Review - North Atlantic Climate Variability: Phenomena, Impacts and MechanismsJ. Marshall, Y. Kushnir, D. Battisti, P. Chang, A. Czaja, R. Dickson, J. Hurrell, M. McCartney, ... | International Journal of Climatology, 2001 [+]
    Abstract: Variability of the North Atlantic Oscillation and the Tropical Atlantic dominate the climate of the North Atlantic sector, the underlying ocean and surrounding continents on interannual to decadal time scales. Here we review these phenomena, their climatic impacts and our present state of understanding of their underlying cause.
  • Looking for the Role of the Ocean in Tropical Atlantic Decadal Climate Variability?Richard Seager, Yochanan Kushnir, Ping Chang, Naomi Naik, Jennifer Miller, and Wilco Hazeleger | Journal of Climate, 2001 [+]
    Abstract: Ocean models are used to investigate how variations in surface heat fluxes and ocean heat transports contribute to variations of tropical Atlantic SSTs on decadal timescales. The observed patterns of variability, deduced from reanalyses of the National Centers for Environmental Prediction (NCEP), are found to involve the ocean’s response to variations in the strength of the northeast and southeast trades. Stronger trade winds are associated with anomalously cool surface temperatures. The trade winds and surface temperatures in each hemisphere appear to behave independently but each is associated with anomalous cross-equatorial ?ow. A numerical model is used in an attempt to simulate this variability. The model is an ocean general circulation model coupled to a simple model of the atmospheric mixed layer and is forced by NCEP winds from 1958 to 1998. The model reasonably reproduces the observed variability. Analysis of the ocean model’s mixed layer energy budget shows that, on decadal timescales, the surface temperature variability is forced by the changes in surface fluxes and is damped by changes in the ocean heat transport. The changes in ocean heat transport are dominated by the horizontal advection of anomalous temperatures by the mean meridional currents. If advection of the mean SST field by anomalous currents is neglected, then the history of observed surface temperatures can still be adequately represented. If advection of the anomalous SSTs by the mean circulation is also neglected, then the model significantly overestimates the surface temperature anomalies but reproduces their temporal evolution. In the more complete models, between 158N and 158S, the changes in ocean heat transport are largely in phase with the changes in surface heat fluxes and SST. Evidence for ocean heat transport either leading or lagging development of surface temperature anomalies is weak in the deep Tropics but appears more persuasive in the northern subtropics. Consistent with these findings, SST anomalies are largely stationary in the deep Tropics but appear to propagate poleward in the northern subtropics. Nonetheless these results suggest that the role of the ocean in tropical Atlantic decadal climate variability is largely passive and damping. Differences with other models that show a more critical role for the ocean, and relevance to reality, are discussed.
  • The North Atlantic OscillationJames W. Hurrell, Yochanan Kushnir, Martin Visbeck | Science Magazine, 2001 [+]
    Abstract: Surface temperatures over the Northern Hemisphere (NH) are likely to be warmer now than at any other time over the past millennium. The rate of warming has been especially high in the past 40 years or so. A substantial fraction of this most recent warming is accounted for by a remarkable upward trend in the North Atlantic Oscillation (NAO). The NAO dictates climate variability from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic, especially during winter. Agricultural yields, water management, and fish inventories, among many other things, are directly affected by the NAO. Yet despite this pronounced influence, scientists remain puzzled about which climate processes govern NAO variability (especially its recent trend), how the phenomenon has varied in the past or will vary in the future, and whether it is at all predictable.
  • Use of data assimilation via linear low-order models for the initialization of El Nino-Southern ...Rafael Cañizares, Alexey Kaplan, Mark A. Cane, Dake Chen, and Stephen E. Zebiak | Journal of Geophysical Research, 2001 [+]
    Abstract: The utility of a Kalman filter (KF) for initialization of an intermediate nonlinear coupled model for El Niño – Southern Oscillation prediction is studied via an approximation of the nonlinear coupled model by a system of seasonally dependent linear models. The low-dimensional nature of such an approximation allows one to determine a sequence of “perfect” initial states that start a trajectory segment best fitting the observed data. Defining these perfect initial conditions as “true” states of the model, we compute a priori parameters of the KF and test its ability to produce an estimate of the “truth” superior to the less theoretically sound estimates. We find that in this application such a KF does not produce an estimate outperforming a pure observational projection as an initial condition for the coupled model forecast. The violation of standard KF assumptions on temporal whiteness of observational errors and system noise is identified as the reason for this failure.
  • The ENSO Teleconnection to the Tropical Atlantic Ocean: Contributions of the Remote and Local ...Alessandra Giannini, John C. H. Chiang, Mark A. Cane, Yochanan Kushnir, and Richard Seager | Journal of Climate, 2001 [+]
    Abstract: Recent developments in Tropical Atlantic Variability (TAV) identify the El Nin˜o–Southern Oscillation (ENSO) as one of the leading factors in the interannual climate variability of the basin. An ENSO event results in Tropicwide anomalies in the atmospheric circulation that have a direct effect on precipitation variability, as well as an indirect effect, that is, one mediated by sea surface temperature (SST) anomalies generated in the remote ocean basins. In order to separate the relative contributions of the atmospheric and oceanic components of the ENSO teleconnection to the tropical Atlantic Ocean, results from two ensembles of atmospheric general circulation model (AGCM) experiments, differing in oceanic boundary conditions, are compared. AGCM integrations performed with the Community Climate Model version 3 (CCM3), forced by global, observed SST during 1950–94 reproduce the observed ENSO-related rainfall anomalies over the tropical Americas and adjacent Atlantic. A parallel ensemble of integrations, forced with observed SST in the tropical Atlantic only, and climatology elsewhere, is used to separate the effect of the direct atmospheric teleconnection from the atmosphere’s response to the ENSO-forced SST anomalies in the Atlantic basin. It is found that ENSO-related atmospheric and oceanic anomalies force rainfall anomalies of the same sign in northeast Brazil, of opposite sign in the Caribbean basin. The direct atmospheric in?uence of a warm ENSO event reduces model rainfall as a whole over the tropical Atlantic basin. This observation is consistent with the hypothesis that an ENSO-related Tropic-wide warming of the free troposphere forces the vertical stabilization of the tropical atmosphere. ENSO-related atmospheric anomalies are also known to force a delayed (relative to the mature phase of ENSO) warming of tropical North Atlantic SST through the weakening of the northeasterly trade winds and consequent reduction of surface ?uxes. It is found that this delayed oceanic component forces a northward displacement of the Atlantic intertropical convergence zone, resulting in increased precipitation over the Caribbean and reduced precipitation over northeast Brazil during the boreal spring following the mature phase of ENSO.
  • Patterns of Coherent Decadal and Interdecadal Climate Signals in the Pacific Basin during the ...Yves M. Tourre, Balaji Rajagopalan, Yochanan Kushnir, Mathew Barlow, and Warren B. White | Geophysical Research Letters, 2001 [+]
    Abstract: Two distinct low-frequency fluctuations are suggested from a joint frequency domain analysis of the Pacific Ocean (30°S-60°N) sea surface temperature (SST) and sea level pressure (SLP). The lowest frequency signal reveals a spatially coherent interdecadal evolution. In-phase SST and SLP anomalies are found along the subarctic frontal zone (SAFZ). It is symmetric about the equator, with tropical SST anomalies peaking near 15° latitudes in the eastern Pacific. The other low-frequency signal reveals a spatially coherent decadal evolution. It is primarily a low-latitude phenomenon. Tropical SST anomalies peak in the central equatorial ocean with evidence of atmospheric teleconnections. These interdecadal and decadal signals join the ENSO and quasi-biennial signals in determining dominant patterns of Pacific Ocean natural climate variability. Relative phasing and location of the SST and SLP anomalies for the decadal, ENSO, and the quasi-biennial signals, are similar to one another but significantly different from that of the interdecadal signal.
  • Regional Rainfall Forecasting using Large Scale Climate Teleconnections and Artificial IntelligenceD. Nagesh Kumar, M. Janga Reddy and Rajib Maity | Journal of Intelligent Systems [+]
    Abstract: This paper presents an Artificial Intelligence approach for regional rainfall forecasting for Orissa state, India on monthly and seasonal time scales. The possible relation between regional rainfall over Orissa and the large scale climate indices like El-Niño Southern Oscillation (ENSO), EQUitorial INdian Ocean Oscillation (EQUINOO) and a local climate index of Ocean-Land Temperature Contrast (OLTC) are studied first and then used to forecast monsoon rainfall. To handle the highly non-linear and complex behavior of the climatic variables for forecasting the rainfall, this study employs Artificial Neural Networks (ANNs) methodology. To optimize the ANN architecture, Genetic Optimizer (GO) is used. After identifying the lagged relation between climate indices and monthly rainfall, the rainfall values are forecast for the summer monsoon months of June, July, August, and September (JJAS) individually, as well as for total monsoon rainfall. The models are trained individually for monthly and for seasonal rainfall forecasting. Then the trained models are tested to evaluate the performance of the model. The results show reasonably good accuracy for monthly and seasonal rainfall forecasting. This study emphasizes the value of using large-scale climate teleconnections for regional rainfall forecasting and the significance of Artificial Intelligence approaches like GO and ANNs in predicting the uncertain rainfall.
  • Wind-Driven Shifts in the Latitude of the Kuroshio-Oyashio Extension and Generation of SST ...Richard Seager, Yochanan Kushnir, Naomi H. Naik, Mark A. Cane, and Jennifer Miller | Journal of Climate [+]
    Abstract: The causes of decadal variations of North Pacific sea surface temperatures (SSTs) are examined using a hindcast performed with an ocean general circulation model thermodynamically coupled to an atmospheric mixed layer model (OGCM–AML model) and forced by the time history of observed surface winds. The ‘‘shift’’ in North Pacific Ocean climate that occurred around 1976/77 is focused on since this is the best observed example available. After the 1976/77 shift the Aleutian low deepened and moved to the southeast of its previous position. This placed anomalous cyclonic flow over the North Pacific. The SST response, as simulated by the ocean model, consisted of two components: a fast and local part and a delayed and remote part. In the central Pacific stronger westerlies cool the ocean by increased equatorward Ekman drift. Here the dynamical cooling is sufficiently large that the surface ?uxes damp the SST anomaly. This Ekman response is fast and local and cools the SSTs beginning in 1977 and persisting through 1988. In the early 1980s cool SSTs emerge in the latitude of the Kuroshio–Oyashio Extension east of Japan and persist until 1989. It is shown that this region of cooling is associated with a southward displacement of the latitude of the confluence between the subpolar and subtropical gyres. This is consistent with the southward shift in the zero wind stress curl line. The timescale for the gyre adjustment is no more than 4 yr. These results compare favorably with observations that also first show the central Pacific cooling and, later, cooling east of Japan. Observations show the cooling in the Kursohio–Oyashio Extension region to be damped by surface fluxes, implying an oceanic origin. The timescale of adjustment is also supported by analyses of observations. The delayed response of the ocean to the varying winds therefore creates SST anomalies as the latitude of the gyre confluence varies. The delayed SST response is of the same sign as the locally forced SST signal suggesting that, to the extent there is a feedback, it is positive. Implications for the origins of decadal climate variability of the North Pacific are discussed.
  • Will Climate Change Exacerbate or Mitigate Water Stress in Central Asia?Tobias Siegfried et al | Working Paper [+]
    Abstract: Millions of people in the geopolitically important region of Central Asia depend on water from snow and glacier melt driven international rivers, most of all the Syr Darya and Amu Darya. The riparian countries of these rivers have experienced recurring water allocation conflicts ever since the Soviet Union collapsed. Will climate change exacerbate water stress and thus conflicts? We have developed a coupled climate – land ice – rainfall – runoff model for the Syr Darya to quantify impacts and show that climatic changes are likely to have a major consequences on runoff seasonality due to earlier snow melt. This will increase water stress because less water will be available for irrigation in the summer months. Threats from geohazards, above all glacier lake outbursts, are likely to increase as well. The area at highest risk is the densely populated, agriculturally productive, and politically unstable Fergana Valley. Major international initiatives to improve water management institutions and infrastructure are required.
  • The Role of Monthly Updated Climate Forecasts in Improving Intraseasonal Water AllocationA. Sankarasubramanian, Upmanu Lall, Naresh Devineni, Susan Espinueva | Journal of Applied Meteorology and Climatology [+]
    Abstract: Seasonal streamflow forecasts contingent on climate information are essential for short-term planning (e.g., water allocation) and for setting up contingency measures during extreme years. However, the water allocated based on the climate forecasts issued at the beginning of the season needs to be revised using the updated climate forecasts throughout the season. In this study, reservoir inflow forecasts downscaled from monthly updated precipitation forecasts from ECHAM4.5 forced with "persisted" SSTs were used to improve both seasonal and intraseasonal water allocation during the October-February season for the Angat reservoir, a multipurpose system, in the Philippines. Monthly updated reservoir inflow forecasts are ingested into a reservoir simulation model to allocate water for multiple uses by ensuring a high probability of meeting the end-of-season target storage that is required to meet the summer (March-May) demand. The forecastbased allocation is combined with the observed inflows during the season to estimate storages, spill, and generated hydropower from the system. The performance of the reservoir is compared under three scenarios: forecasts issued at the beginning of the season, monthly updated forecasts during the season, and use of climatological values. Retrospective reservoir analysis shows that the operation of a reservoir by using monthly updated inflow forecasts reduces the spill considerably by increasing the allocation for hydropower during above-normal-inflow years. During below-normal-inflow years, monthly updated streamflow forecasts could be effectively used for ensuring enough water for the summer season by meeting the end-of-season target storage. These analyses suggest the importance of performing experimental reservoir analyses to understand the potential challenges and opportunities in improving seasonal and intraseasonal water allocation by using real-time climate forecasts.
  • Will U.S. Agriculture Really Benefit from Global Warming? Accounting for Irrigation in the ...Wolfram Schlenker, W. Michael Hanemann, and Anthony C. Fisher | The American Economic Review [+]
    Abstract: There has been a lively debate about the potential impact of global climate change on U.S. agriculture. Most of the early agro-economic studies predicted large damages (see, for example, Richard M. Adams, 1989; Harry M. Kaiser et al., 1993; Adams et al., 1995). In an innovative paper Robert Mendelsohn, William D. Nordhaus and Daigee Shaw (1994), hereafter MNS, propose a new approach: using the variation in temperature and precipitation across U.S. counties to estimate a reduced-form hedonic equation with the value of farmland as the dependent variable. A change in temperature and/or precipitation is then associated with a change in farmland value, which can be interpreted as the impact of climate change. Adams et al. (1998) characterize the hedonic approach as a spatial analogue approach. They acknowledge that "the strength of the spatial analogue approach is that structural changes and farm responses are implicit in the analysis, freeing the analyst from the burden of estimating the effects of climate change on particular region-specific crops and farmer responses." One of the potential disadvantages, however, of the hedonic approach is that it is a partial equilibrium analysis, i.e., agricultural prices are assumed to remain constant. While year-to-year fluctuations in annual weather conditions certainly have the potential to have an impact on current commodity prices, especially for crops produced only in a relatively localized area (such as citrus fruits grown mainly in California and Florida), changes in long-run weather patterns (i.e., changes in climate) might have a smaller effect on commodity prices because of the greater potential for economic adaptation, particularly shifts in growing regions.2 The hedonic approach as implemented by MNS predicts that existing agricultural land on average might be more productive and hence result in benefits for U.S. farmers. The hedonic approach has received considerable attention in our judgment, in part because the conclusions are at variance with those of some other studies that suggest warming will lead to damages, and in part because of the new methodology. Although the approach is appealing, it is also vulnerable to problems related to misspecification.
  • The evolution of El Niño, past and futureMark A. Cane | Earth and Planetary Science Letters [+]
    Abstract: We review forecasts of the future of El Niño and the Southern Oscillation (ENSO), a coupled instability of the ocean-atmosphere system in the tropical Pacific with global impacts. ENSO in the modern world is briefly described, and the physics of the ENSO cycle is discussed. Particular attention is given to the Bjerknes feedback, the instability mechanism which figures prominently in ENSO past and future. Our knowledge of ENSO in the paleoclimate record has expanded rapidly within the last 5 years. The ENSO cycle is present in all relevant records, going back 130 kyr. It was systematically weaker during the early and middle Holocene, and model studies show that this results from reduced amplification of anomalies in the late summer and early fall, a consequence of the altered mean climate in response to boreal summer perihelion. Data from corals shows substantial decadal and longer variations in the strength of the ENSO cycle within the past 1000 years; it is suggested that this may be due to solar and volcanic variations in solar insolation, amplified by the Bjerknes feedback. There is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future, but it is very far from conclusive. The comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of ENSO’s future. Some predict more ENSO activity, some less, with the highly uncertain consensus forecast indicating little change.
  • Spatiotemporal Structure of Tropical Moisture Exports and their Precursors associated with High Precipitation induced Floods over the Continental United States
  • Transport in the Hudson Estuary: A Modeling Study of Estuarine Circulation and Tidal TrappingF. L. Hellweger, A. F. Blumberg, P. Schlosser, D. T. Ho, T. Caplow, U. Lall, and H. Li | Estuarine Research Foundation [+]
    Abstract: The effects of estuarine circulation and tidal trapping on transport in the Hudson estuary were investigated by a large-scale, high-resolution numerical model simulation of a tracer release. The modeled and measured longitudinal profiles of surface tracer concentrations (plumes) differ from the ideal Gaussian shape in two ways: on a large scale the plume is asymmetric with the downstream end stretching out farther, and small-scale (1-2 km) peaks are present at the upstream and downstream ends of the plume. A number of diagnostic model simulations (e.g., remove freshwater flow) were performed to understand the processes responsible for these features. These simulations show that the large-scale asymmetry is related to salinity. The salt causes an estuarine circulation that decreases vertical mixing (vertical density gradient), increases longitudinal dispersion (increased vertical and lateral gradients in longitudinal ve- locities), and increases net downstream velocities in the surface layer. Since salinity intrusion is confined to the down- stream end of the tracer plume, only that part of the plume is effected by those processes, which leads to the large- scale asymmetry. The small-scale peaks are due to tidal trapping. Small embayments along the estuary trap water and tracer as the plume passes by in the main channel. When the plume in the main channel has passed, the tracer is released back to the main channel, caiising a secondary peak in the longitudinal profile.
  • The role of soil moisture initialization in subseasonal and seasonal streamflow prediction ...Sarith P.P. Mahanama, Randal D. Koster, Rolf H. Reichle, Lareef Zubair | Advances in Water Resources [+]
    Abstract: The two main contributors to streamflow predictability at subseasonal to seasonal timescales in tropical regions are: (i) the predictability of meteorologic (particularly precipitation) anomalies, and (ii) the land surface soil moisture state at the start of the forecast period. Meteorological predictions at subseasonal timescale are usually fraught with error and may not be dependable. The accurate initialization of soil moisture, as obtained through real-time land data analysis, may provide skill in subseasonal to seasonal streamflow prediction, even when the prediction skill for rainfall is small. A series of experiments using the Catchment Land Surface Model (CLSM) is performed to characterize the contribution of accurate soil moisture initialization to the skill of streamfkow prediction in Sri Lanka at timescales up to 2 months. We find that at the monthly timescale, accurate soil moisture initialization provides between 10% and 60% of the total runoff prediction skill that could be obtained under a perfect prediction of meteorological forcing. Some contributions to streamflow forecast skill are also found for the second month of forecast.
  • Use of seasonal climate information to predict coconut production in Sri LankaT. S. G. Peiris, J. W. Hansen and Lareef Zubair | International Journal of Climatology [+]
    Abstract: Accurate forecasting of annual national coconut production (ANCP) is important for national agricultural planning and negotiating forward contracts. Climate and the long-term trends (attributed to ‘technology’) are major factors that determine ANCP. The effect of climate on ANCP of the following year was studied for the seven agro-ecological regions (AER’s) in the principal coconut growing areas for the period 19502002. Climate was studied based on seasons aggregated by the monsoon calendar and by quarters that are consistent with the agricultural calendar. The use of quarterly seasons explained more of the variability of ANCP than the use of monsoon based seasons. January–March rainfall in all AER’s and July–September rainfall in the wetter regions are positively correlated with the ANCP (p < 0.005). The technology effect was estimated using a log–linear trend model. The regression model integrates both climate and technology effects developed to predict ANCP with high ?delity (R 2 = 0.94). The climate effect was estimated by regressing production data that had been de-trended to remove the technology effects with quarterly rainfall in the year prior to harvest. The most signi?cant predictors were found to be the quarterly rainfall from the AER’s in the coconut growing regions that are designated as wet and intermediate. Representative rainfall from each quarter was used in a regression model with corrections for the technology effect. The correlation between observed and predicted values of the ANCP was 0.83 (p < 0.001). The prediction of ANCP for 2003 and 2004 gave errors of only 6.5 and 7.0%. The estimated value of ANCP for 2005 is 2715 million nuts, which is 12% higher than the mean. The lead time of the prediction extends to 15 months but it may be extended with the use of seasonal climate forecasts to 24 months.
  • Statistical Prediction of ENSO from Subsurface Sea Temperature Using a Nonlinear Dimensionality ...Carlos H. R. Lima and Upmanu Lall; Tony Jebara; Anthony G. Barnston | Journal of Climate [+]
    Abstract: Numerous statistical and dynamical models have been developed in recent years to forecast ENSO events. However, for most of these models predictability for lead times over 10 months is limited. It has been hypothesized that the tropical Pacific thermocline structure may have critical information to permit longer lead ENSO forecasts. Models that use subsurface sea temperature information have already been known to produce better long lead forecasts. Here, a two-stage statistical ENSO forecasting model is developed and demonstrated using the spatially distributed depth of the 208C isotherm (D20 ) as a proxy for the thermocline. In the first stage, a nonlinear dimension reduction method [maximum variance unfolding (MVU)] is used to decompose the D20 data into canonical modes. The leading spatial patterns as well as lagged values of Nin˜o-3 are then used as predictors in a set of linear regression models to predict the Nin˜o-3 index at lead times of up to 24 months. Cross-validated forecasts using this methodology are shown to have higher skill than those that use a dimension reduction of the same thermocline data using principal component analysis (PCA). The first three modes of the D20 data as revealed by MVU account for 89% of the variance of the data, as compared to only 48% of the variance if PCA is used. The spatial patterns of the MVU modes partition the data field in a different way than the PC modes, even though some similarities exist as to the main regions that are active. These patterns and their temporal structure are discussed here, with a view to understanding the possible source of the longer-range predictability of ENSO using the MVU modes. The skill of the PCA- and the MVU-based forecasts of Nin˜ o-3 varies depending on the starting month of the forecast for short lead times (5– 10 months). However, for the lead times longer than 1 yr, the MVU-based forecast skill is not seasonally variable, while the PCA-based models do not provide significant skill at these lead times irrespective of the starting month of the forecast. Similar conclusions are obtained for forecast models for the Nin˜o-3.4 and Nin˜o- 1.2 indices. The differences between the MVU- and PCA-based models are most marked for the Nin˜o-1.2 long lead forecasts.
  • Sustainable fisheriesGeoffrey Heal and Wolfram Schlenker | Nature [+]
    Abstract: Fishermen’s aims of increasing their catch seem at odds with preserving fish stocks by limiting catch. A study of more than 11,000 fisheries shows that ‘individual tradable quotas’ can reconcile these goals
  • Surface Water Mixing in the Solomon Sea as Documented by a High-Resolution Coral 14C RecordT. P. Guilderson, D. P. Schrag, and M. A. Cane | Journal of Climate
  • Stochastic simulation model for nonstationary time series using an autoregressive wavelet ...Kwon H.-H., U. Lall, A. F. Khalil | Water Resources Research [+]
    Abstract: A time series simulation scheme based on wavelet decomposition coupled to an autoregressive model is presented for hydroclimatic series that exhibit band-limited lowfrequency variability. Many nonlinear dynamical systems generate time series that appear to have amplitude- and frequency-modulated oscillations that may correspond to the recurrence of different solution regimes. The use of wavelet decomposition followed by an autoregressive model of each leading component is explored as a model for such time series. The first example considered is the Lorenz-84 low-order model of extratropical circulation, which has been used to illustrate how chaos and intransitivity (multiple stable solutions) can lead to low-frequency variability. The central England temperature (CET) time series, the NINO3.4 series that is a surrogate for El Nino–Southern Oscillation, and seasonal rainfall from Everglades National Park, Florida, are then modeled with this approach. The proposed simulation model yields better results than a traditional linear autoregressive (AR) time series model in terms of reproducing the time-frequency properties of the observed rainfall, while preserving the statistics usually reproduced by the AR models.
  • Statistical-Dynamical Approach for Streamflow Modeling at Malakal, Sudan, on the White Nile RiverPaul J. Block and Balaji Rajagopalan | Journal of Hydrologic Engineering [+]
    Abstract: The upper White Nile Basin above Malakal, Sudan, is considered to be one of the most complicated and diverse hydrologic settings on Earth. Accurately depicting and predicting the streamflow at Malakal is essential for water managers considering Nile Basin-wide initiatives and potential large-scale projects. Dynamical, statistical, and combination models are assessed for their ability to predict monthly streamflow at Malakal. The dynamical model represents a lumped parameter, average-monthly water balance, whereas the statistical model incorporates a nonparametric approach based on local polynomial regression, utilizing principal components of precipitation and temperature. The combination of dynamical and statistical models through linear regression produces model weights of 0.44 and 0.59, respectively, implying a relatively balanced influence. Evaluation of the combination model demonstrates significant overall skill correlation coefficients equal to 0.83, outperforming either individual model for the validation periods selected. Peak streamflow analyses of timing and quantity also exhibit superior performance by the combination model. An ensemble approach, practical for planning and management from a probabilistic standpoint, is additionally demonstrated.
  • The Effects of Sea-Ice and Land-Snow Concentrations on Planetary Albedo from the Earth Radiation ...Irina V. Gorodetskaya, Mark A. Cane, L.-Bruno Tremblay, and Alexey Kaplan | Atmosphere-Ocean [+]
    Abstract: The high-latitude ice/snow-albedo feedback is a principal element in many paleoclimate theories and global warming scenarios. The strength of this feedback is determined by the ice/snow effects on the top-of-atmosphere (TOA) albedo, which is also strongly affected by clouds. Using currently available satellite observations, we estimate the radiative effectiveness (RE) of ice and snow with regards to the TOA albedo, which we define as the change in the TOA albedo corresponding to changes of 0% to 100% in the ice or snow cover. The REs of the northern hemisphere (NH) sea ice, land snow, and southern hemisphere (SH) sea ice are found to be 0.22, 0.23 and 0.16, respectively. This means that, for an incident solar flux of about 400 W m–2 reaching the TOA in the polar latitudes in summer, local reduction in ice/snow concentrations from 100% to 0% will result in a decrease in reflected short wave radiation of approximately 80 W m–2 . These changes in the TOA albedo are significant, yet smaller than the associated changes in the surface albedo. Comparison of the TOA albedo values with available surface albedo observations helps to identify the role of clouds in the RE of ice/snow. The analysis is based on the whole time-space domain where the sea ice and land snow appear, and reveals a remarkable similarity in the ice and snow RE in the areas with high sea-ice and land-snow cover variability, despite the varying nature of the surface cover, seasonality, and locations. These estimates provide a useful constraint to test current climate models.
  • Vulnerability and adaptation to climate variability and water stress in Uttarakhand State, IndiaUlka Kelkar, Kapil Kumar Narula, Ved Prakash Sharma, Usha Chandna | Global Environmental Change [+]
    Abstract: This paper presents a participatory approach to investigate vulnerability and adaptive capacity to climate variability and water stress in the Lakhwar watershed in Uttarakhand State, India. Highly water stressed microwatersheds were identified by modelling surface runoff, soil moisture development, lateral runoff, and groundwater recharge. The modelling results were shared with communities in two villages, and timeline exercises were carried out to allow them to trace past developments that have impacted their lives and livelihoods, and stimulate discussion about future changes and possible adaptation interventions.
  • The impact of precession changes on the Arctic climate during the last interglacial-glacial ...Myriam Khodri, Mark A. Cane, George Kukla, Joyce Gavin, and Pascale Braconnot | Earth and Planetary Science Letters [+]
    Abstract: Three sensitivity experiments using an Ocean Atmosphere General Circulation Model (OAGCM) are conducted to simulate the climate impact of precession. The relative contributions of components of the hydrological cycle including the albedo of Arctic sea ice, advection of atmospheric water vapor and sea surface temperature to the summer Arctic melt process are evaluated. Timing of the perihelion is varied in each experiment with meteorological spring (SP), winter (WP) and autumn (AP) perihelion corresponding to conditions at 110, 115 and 120 ky BP, respectively. Obliquity is unchanged at the 115 ky level which is lower than today. The experiments are assessed relative to the present day control, which has been shown to simulate current conditions based on observations. In the SP experiment, top of the atmosphere (TOA) insolation is weaker than today between the summer solstice and autumnal equinox. In the AP case representing the interglacial, it is less intense between vernal equinox and summer solstice but stronger during the remainder of the year. Although the incident solar radiation is reduced in summer in the SP experiment, increased melting of snow is found primarily as a result of feedbacks from the delayed seasonal cycle of hydrologic components. This is in contrast to both the WP and AP cases in which the perennial snow cover is simulated. At the time of the last glacial inception, 115 ky BP, the WP experiment shows lower insolation to the high northern latitudes in late spring and summer mainly as a result of lower obliquity than today. Dynamical ocean–atmosphere interactions in response to precession maintain the reduced sea ice melting in late spring, strengthen the annual equator-to-pole sea surface temperature (SST) gradient and increase atmospheric moisture convergence in glaciation-sensitive regions. In both the WP and AP experiments seasonal sea ice melting is weakened resulting in pronounced outgoing radiative flux at the locations of expanded sea ice. This leads to further cooling and increased snowfall due to the reduced atmospheric water holding capacity and increased atmospheric moisture convergence from the subtropical Atlantic. In agreement with Milankovitch theory, our results show favorable conditions for glacial inception at 115 ky BP but with obliquity unchanged, they also show perennial snow cover at 120 ky BP resulting from the reduced strength of spring insolation.
  • Review of Hydroclimatic Teleconnection Between Hydrologic Variables and Large Scale Atmoshpheric CirculationRajib Maity, D. Nagesh Kumar and Ravi S. Nanjundiah | Indian Society for Hydraulics Journal of Hydraulic Engineering [+]
    Abstract: Hydroclimatic teleconnection between hydrologic variables and large-scale atmospheric circulation phenomena is being studied worldwide and gaining more and more interest in recent years due to its potential use in hydrologic time series analysis and forecasting. In this paper a review of such related work is presented. First, characteristics of major large-scale atmospheric circulation phenomena from tropical Pacific Ocean and Indian Ocean region are explained. El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) mode from tropical Pacific Ocean and Indian Ocean respectively are selected and their global influences on hydrologic variables through hydroclimatic teleconnection are elaborated. Potential predictive power of such large-scale indices for hydrologic variables is explained based on the established research work across the world. Research opportunities, in this direction, are then explained in Indian perspective. A preliminary analysis is also presented in this regard. Predictive potential of such large-scale indices is of immense use to water resources community.
  • The Turn of the Century North American Drought: Global Context, Dynamics, and Past AnalogsRichard Seager | Journal of Climate [+]
    Abstract: The causes and global context of the North American drought between 1998 and 2004 are examined using atmospheric reanalyses and ensembles of atmosphere model simulations variously forced by global SSTs or tropical Pacific SSTs alone. The drought divides into two distinct time intervals. Between 1998 and 2002 it coincided with a persistent La Niña–like state in the tropical Pacific, a cool tropical troposphere, poleward shifted jet streams, and, in the zonal mean, eddy-driven descent in midlatitudes. During the winters reduced precipitation over North America in the climate models was sustained by anomalous subsidence and reductions of moisture convergence by the stationary flow and transient eddies. During the summers reductions of evaporation and mean flow moisture convergence drove the precipitation reduction, while transient eddies acted diffusively to oppose this. During these years the North American drought fitted into a global pattern of circulation and hydroclimate anomalies with noticeable zonal and hemispheric symmetry. During the later period of the drought, from 2002 to 2004, weak El Niño conditions prevailed and, while the global climate adjusted accordingly, western North America remained, uniquely among midlatitude regions, in drought. The ensemble mean of the climate model simulations did not simulate the continuation of the drought in these years, suggesting that the termination of the drought was largely unpredictable in terms of global ocean conditions. The global context of the most recent, turn of the century, drought is compared to the five prior persistent North American droughts in the instrumental record from the mid-nineteenth century on. A classic La Niña pattern of ocean temperature in the Pacific is common to all. A cold Indian Ocean, also typical of La Niña, is common to all five prior droughts, but not the most recent one. Except in southern South America the global pattern of precipitation anomalies of the turn of the century drought is similar to that during the five prior droughts. These comparisons suggest that the earlier period of this most recent drought is the latest in a series of multiyear droughts forced by persistent changes in tropical Pacific Ocean temperatures. Warm tropical North Atlantic Ocean temperatures may play a secondary role.
  • Role of Predictors in downscaling surface temperature to river basin in India for IPCC SRES ...Aavudai Anandhi, V. V. Srinivas, D. Nagesh Kumar, and Ravi S. Nanjundiah | International Journal of Climatology [+]
    Abstract: In this paper, downscaling models are developed using a support vector machine (SVM) for obtaining projections of monthly mean maximum and minimum temperatures (Tmax and Tmin) to river-basin scale. The effectiveness of the model is demonstrated through application to downscale the predictands for the catchment of the Malaprabha reservoir in India, which is considered to be a climatically sensitive region. The probable predictor variables are extracted from (1) the National Centers for Environmental Prediction (NCEP) reanalysis dataset for the period 1978–2000, and (2) the simulations from the third-generation Canadian Coupled Global Climate Model (CGCM3) for emission scenarios A1B, A2, B1 and COMMIT for the period 1978–2100. The predictor variables are classi?ed into three groups, namely A, B and C. Large-scale atmospheric variables such as air temperature, zonal and meridional wind velocities at 925 mb which are often used for downscaling temperature are considered as predictors in Group A. Surface ?ux variables such as latent heat (LH), sensible heat, shortwave radiation and longwave radiation fluxes, which control temperature of the Earth’s surface are tried as plausible predictors in Group B. Group C comprises of all the predictor variables in both the Groups A and B. The scatter plots and cross-correlations are used for verifying the reliability of the simulation of the predictor variables by the CGCM3 and to study the predictor-predictand relationships. The impact of trend in predictor variables on downscaled temperature was studied. The predictor, air temperature at 925 mb showed an increasing trend, while the rest of the predictors showed no trend. The performance of the SVM models that are developed, one for each combination of predictor group, predictand, calibration period and location-based stratification (land, land and ocean) of climate variables, was evaluated. In general, the models which use predictor variables pertaining to land surface improved the performance of SVM models for downscaling Tmax and Tmin.
  • Role of price and enforcement in water allocation: Insights from Game TheoryFrancisco Assis Souza Filho, Upmanu Lall, and Rubem La Laina Porto | Water Resources Research [+]
    Abstract: As many countries are moving toward water sector reforms, practical issues of how water management institutions can better effect allocation, regulation, and enforcement of water rights have emerged. The problem of nonavailability of water to tailenders on an irrigation system in developing countries, due to unlicensed upstream diversions is well documented. The reliability of access or equivalently the uncertainty associated with water availability at their diversion point becomes a parameter that is likely to influence the application by users for water licenses, as well as their willingness to pay for licensed use. The ability of a water agency to reduce this uncertainty through effective water rights enforcement is related to the fiscal ability of the agency to monitor and enforce licensed use. In this paper, this interplay across the users and the agency is explored, considering the hydraulic structure or sequence of water use and parameters that define the users and the agency’s economics. The potential for free rider behavior by the users, as well as their proposals for licensed use are derived conditional on this setting. The analyses presented are developed in the framework of the theory of ‘‘Law and Economics,’’ with user interactions modeled as a game theoretic enterprise. The state of Ceara, Brazil, is used loosely as an example setting, with parameter values for the experiments indexed to be approximately those relevant for current decisions. The potential for using the ideas in participatory decision making is discussed. This paper is an initial attempt to develop a conceptual framework for analyzing such situations but with a focus on the reservoir-canal system water rights enforcement.
  • War20: Three Reasons that Violence Could EruptTobias Siegfried | SEED Magazine [+]
    Abstract: On our planet freshwater resources are unevenly distributed, in space and time. Especially in the drylands, where demand chronically outstrips renewable supply, management is a challenge. And it will certainly remain one in the future, given increasing population pressure and large future climate uncertainty, as well as ongoing freshwater resources depletion and degradation due to misallocation. The truth is that conflicts over water resources abound even nowadays. So the relevant questions become: Under which circumstances can those conflicts, if at all, spill over into armed violence? Could water wars eventually emerge as a defining feature of the geography of conflict?
  • Towards Optimal Reconstruction of Ocean Surface Flux Fields: Exploring Wind Stress - Sea Level ...Alexey Kaplan, Donna Witter, Mark Cane, and Yochanan Kushnir | World Meteorological Organization [+]
    Abstract: We approach the problem of analysis of historical ocean-atmosphere flux fi elds as a general problem of the least squares based analysis of time-evolving fields. The typical sources of information for such analyses are imperfect models (prognostic models for time transitions or diagnostic constraints) and incomplete and erratic observations. This problem is central in two areas of climate research which traditionally are considered separately: assimilation of data into numerical models and objective analyses (reconstructions) of data sets of historical observations. (In fact the main di fference between the s e two types of problems is in a relative amount of information brought by the model vs observations: it is low in the latter problem and high in the former.) Least squares procedures of optimal estimation, when applied to gappy and erratic data, result in the solutions which predominantly project onto the mo st energetic patterns of a priori error covariance. This property of the solution allows to combine the classical least squares technique with the approach of a space reduction in order to develop a computationally e ffective procedure of objective analysis for observe d historical climate fields, which are characterized by comparatively precise data and go o d coverage in the last few decade s, and poor observational coverage prior (Kaplan et al., 1997, 2001). Recent applications of the procedure to the historical ship-based data for such flux-relate d variables as sea surface temperature (SST) and s e a level pressure (SLP) resulted in near-global monthly reconstruction from 1850s to present accompanied by veri ed error bars (Kaplan et al., 1998, 2000). We believe that a modi cation of the same approach can be used successfully for objective analyses of interannual variability of surface ux elds, at least for the areas where climatological normals are considered known. We attempt to evaluate a potential of multivariate analyses of surface momentum fluxes with explicit model constraints of local (e.g. geostrophic balance equations) or non-local nature (e.g. dynamical ocean models converting wind stress elds into sea level height observations). For illustration of prospects and diculties of such applications we compare 4 versions of the tropical Paci c surface zonal wind stre s s: a successive correction analysis by Da Silva et al. (1994) (DS), our own trial reduced space optimal interpolation (OI) of global surface winds, surface (10 m) winds from the NCEP-NCAR reanalysis (Kalnay et al., 1996) (RA), and Flor ida State University (FSU) subjective analysis (Goldenb erg and O'Brien, 1981). Our trial OI analysis of surface winds was produced by application of the technique by Kaplan et al. (2000) to to the set of COADS observations (Woodru et al., 1987) correcte d by Da Silva et al. (1994) for systematic biases. The wind stre s s pro duct was obtained by multiplying the analyzed values of wind vector anomalies by climatological wind speed from Da Silva (1994) atlas. Results of comparison based on various criteria are presented in Sec. 2. Our conclusions are given in Sec. 3, and recommendations for the methodological approach to a historical analys i s of the interannual variability of surface fluxes are in Sec. 4.
  • Warren revisited: Atmospheric freshwater fluxes and ‘‘Why is no deep water formed in the North Pacific’’Julien Emile-Geay, Mark A. Cane, Richard Seager, Amy C. Clement, and Alexander van Geen | Journal of Geophysical Research [+]
    Abstract: Warren’s [1983] ‘‘Why is no deep water formed in the North Pacific’’ is revisited. His box model of the northern North Pacific is used with updated estimates of oceanic volume transports and boundary freshwater fluxes derived from the most recent data sets, using diverse methods. Estimates of the reliability of the result and its sensitivity to error in the data are given, which show that the uncertainty is dominated by the large observational error in the freshwater fluxes, especially the precipitation rate. Consistent with Warren’s conclusions, it is found that the subpolar Atlantic-Pacific salinity contrast is primarily explained by the small circulation exchange between the subpolar and subtropical gyres, and by the local excess of precipitation over evaporation in the northern North Pacific. However, unlike Warren, we attribute the latter excess to atmospheric water vapor transports, in particular the northern moisture flux associated with the Asian Monsoon. Thus the absence of such a large transport over the subpolar North Atlantic may partly explain why it is so salty, and why deep water can form there and not in the North Pacific.
  • The relationship between tibetan snow depth, ENSO, river discharge and the monsoons of BangladeshJeffrey Shaman, Mark Cane, and Alexey Kaplan | International Journal of Remote Sensing [+]
    Abstract: Using satellite estimates of snow depth, we examine the interannual variability of the monsoon rains of Bangladesh, an area greatly affected by land surface hydrological processes including Himalayan snowpack size, snowmelt river flooding, and Bay of Bengal storm surge. For the twentieth century, we found Bangladesh monsoon rainfall (BMR) to be uncorrelated with the All-Indian Monsoon Index. This result is consistent with previous findings for shorter time records. We next used a short 9-year record of satellite estimates of April snow depth for the Himalayan region and concurrent seasonal El Nin˜ o–Southern Oscillation (ENSO) conditions in the equatorial Pacific to develop an empirical model that explains a high percentage of BMR interannual variability. Inclusion of late spring river discharge levels further improves the empirical model representation of BMR for June–September. These results, though with a limited length satellite record, suggest that BMR interannual variability is constrained by concurrent ENSO conditions, spring Himalayan snowpack size and land surface flooding. The same results could not be obtained from analyses using satellite estimates of snow cover. These findings stress the need for development of a quality longer record of satellite estimated snow depth. The twentieth-century analysis also indicates that BMR should be considered independently of Indian monsoon rainfall.
  • Is the Gulf Stream responsible for Europes mild winters?R. Seager, D. S. Battisti, J. Yin, N. Gordon, N. Naik, A. C. Clement, and M. A. Cane | Quarterly Journal of the Royal Meteorological Society [+]
    Abstract: Is the transport of heat northward by the Gulf Stream and North Atlantic Drift, and its subsequent release into the midlatitude westerlies, the reason why Europe’s winters are so much milder than those of eastern North America and other places at the same latitude? Here, it is shown that the principal cause of this temperature difference is advection by the mean winds. South-westerlies bring warm maritime air into Europe and northwesterlies bring frigid continental air into north-eastern North America. Further, analysis of the ocean surface heat budget shows that the majority of the heat released during winter from the ocean to the atmosphere is accounted for by the seasonal release of heat previously absorbed and not by ocean heat- ux convergence. Therefore, the existence of the winter temperature contrast between western Europe and eastern North America does not require a dynamical ocean. Two experiments with an atmospheric general-circulation model coupled to an ocean mixed layer confirm this conclusion. The difference in winter temperatures across the North Atlantic, and the difference between western Europe and western North America, is essentially the same in these models whether or not the movement of heat by the ocean is accounted for. In an additional experiment with no mountains, the  flow across the ocean is more zonal, western Europe is cooled, the trough east of the Rockies is weakened and the cold of north-eastern North America is ameliorated. In all experiments the west coast of Europe is warmer than the west coast of North America at the same latitude whether or not ocean heat transport is accounted for. In summary the deviations from zonal symmetry of winter temperatures in the northern hemisphere are fundamentally caused by the atmospheric circulation interacting with the oceanic mixed layer.
  • Climate informed flood frequency analysis and prediction, Montana using hierarchical Bayesian modelsHyun-Han Kwon, Casey Brown and Upmanu Lall | Geophysical Research Letters [+]
    Abstract: It is widely acknowledged that climate variability modifies the frequency spectrum of extreme hydrologic events. Traditional hydrological frequency analysis methods do not account for year to year shifts in flood risk distributions that arise due to changes in exogenous factors that affect the causal structure of flood risk. We use Hierarchical Bayesian Analysis to evaluate several factors that influence the frequency of extreme floods for a basin in Montana. Sea surface temperatures, predicted GCM precipitation, climate indices and snow pack depth are considered as potential predictors of flood risk. The parameters of the flood risk prediction model are estimated using a Markov Chain Monte Carlo algorithm. The predictors are compared in terms of the resulting posterior distributions of the parameters that are used to estimate flood frequency distributions. The analysis shows an approach for exploiting the link between climate scale indicators and annual maximum flood, providing impetus for developing seasonal forecasting of flood risk applications and dynamic flood risk management strategies.
  • Climate informed long term seasonal forecasts of hydroenergy inflow for the Brazilian hydropower ...Carlos H.R. Lima, Upmanu Lall | Journal of Hydrology [+]
    Abstract: Ef?cient management of water and energy is an important goal of sustainable development for any nation. Stream?ow forecasts, have been used in complex optimization models to maximize water use ef?ciency and electrical energy production. In this paper we develop a statistical model for the long term forecasts of hydroenergy in?ow into the Brazilian hydropower system, which consists of more than 70 hydropower reservoirs. At present, the planning of reservoir operation and energy production in Brazil is made with no reliable long term (one season or longer lead times) stream?ow forecasts. Here we use the NINO3 index and the main modes of the tropical Paci?c thermocline structure as climate predictors in order to achieve skillfull forecasts at long leads. Cross-validated results show that about 50% of the total hydroenergy in?ow can be predicted with moderate accuracy up to 20 month lead time.
  • Climate informed monthly streamflow forecasts for the Brazilian hydropower network ...Carlos H.R. Lima, Upmanu Lall | Journal of Hydrology [+]
    Abstract: Streamflow simulation and forecasts have been widely used in water resources management, particularly for flood and drought analysis and for the determination of optimal operational rules for reservoir systems used for water supply and energy production. Here we include climate information in a periodicauto-regressive model in order to provide monthly stream?ow forecasts for 54 hydropower sites in Brazil. Large scale climate information is included in the model through the use of climate indices obtained from the sea surface temperature field of the tropical Pacific and sub-tropical Atlantic oceans and the low-level zonal wind field over southeast Brazil. Correlation analysis of climate predictors and stream- ?ow data show that the dependence of the latter on climate variability is seasonal and also a function of the lead time of the forecasts. A ridge regression framework is adopted in order to shrink parameter estimates and improve model outputs. The proposed model is compared with an ordinary linear regression based model with predictors selected by the BIC criterion and with the classical linear periodic-autoregressive model (PAR), where no climate information is used. Cross-validated results show that the inclusion of climate indexes is able to improve forecast skills up to 3 months lead time. Higher skills are observed for reservoirs with large catchment areas.
  • Climate risk management for water in semi–arid regionsAW Robertson, W Baethgen, P Block, U Lall, A Sankarasubramanian, FS Filho, and KMJ Verbist | Earth Perspectives
  • Climate Change over the Equatorial Indo-Pacific in Global WarmingChie Ihara, Yochanan Kushnir, Mark A. Cane, and Victor H. de la Peña | Journal of Climate
  • Classifying North Atlantic Tropical Cyclone Tracks by Mass MomentsJennifer Nakamura, Upmanu Lall, Yochanan Kushnir and Suzana J. Camargo | Journal of Climate [+]
    Abstract: A new method for classifying tropical cyclones or similar features is introduced. The cyclone track is considered as an open spatial curve, with the wind speed or power information along the curve considered to be a mass attribute. The first and second moments of the resulting object are computed and then used to classify the historical tracks using standard clustering algorithms. Mass moments allow the whole track shape, length, and location to be incorporated into the clustering methodology. Tropical cyclones in the North Atlantic basin are clustered with K-means by mass moments, producing an optimum of six clusters with differing genesis locations, track shapes, intensities, life spans, landfalls, seasonal patterns, and trends. Even variables that are not directly clustered show distinct separation between clusters. A trend analysis confirms recent conclusions of increasing tropical cyclones in the basin over the past two decades. However, the trends vary across clusters.
  • Building the Agenda for Institutional Research in Water Resource ManagementBlomquist, W., T. Heikkila and E. Schlager | Journal of the American Water Resources Association [+]
    Abstract: This paper pursues more specifically the recommendations of a recent National Research Council report recommending greater attention to research on institutions in the field of water resource management. The important challenge for the future in institutional research lies in going beyond the observation that institutions are important and in explaining instead how institutions actually affect management options and outcomes. It is possible to illuminate the relationships between institutional features and water management through comparative institutional research. This paper offers recommendations for studying water institutions in a comparative context, including methodological recommendations concerning approaches to comparative institutional research, and topics for comparative institutional research that appear especially fruitful at this time. The example of conjunctive management is used to illustrate the importance of institutional factors in water management, drawing to some extent on the authors' recent experience with a comparative study of conjunctive management institutions.
  • Challenges to Our Understanding of the General Circulation: Abrupt Climate ChangeRichard Seager and David S. Battisti | Princeton University Press [+]
    Abstract: About 14,700 years ago (14.7 kyr BP), towards the end of the last ice age, the climate warmed dramatically and abruptly around the North Atlantic—by as much as the difference between full glacial and interglacial conditions—in no more than a decade or two. This is all the more remarkable because it occurred in the presence of massive ice sheets and continuation of the albedo forcing that presumably had been helping maintain glacial conditions up to that point. But it was not to last. Sometime just after 13 kyr BP this Bølling-Allerød warm period ended as climate first cooled, and then abruptly cooled, into the so-called Younger Dryas. As near-glacial conditions returned, glaciers advanced in Europe, and the forests that had established themselves in the preceding warm epoch died. The Younger Dryas ended with a second abrupt warming that occurred over only a decade or so and that shifted temperatures back to those of the Holocene and of today. The idea that the climate system goes through such abrupt shifts did not take the climate research community by storm but dribbled into acceptance in the 1980s and the early 1990s. Only when duplicate ice cores said the same thing and the evidence was found in multiple indicators within the ice—oxygen isotopes, dust concentrations, snow accumulation, and so on—and could be correlated with terrestrial and marine records did acceptance that abrupt climate change was a reality sink in. This gradual acceptance is telling. When Hays et al. (1976) showed just how well climate records from deep-sea cores could be matched to orbital cycles, it was deeply satisfying: the gradual waxing and waning of the great ice sheets could be explained by equally gradual changes in the distribution of delivery of solar radiation to the Earth’s surface. Insolation over high northern latitudes was deemed to be particularly important, with reduction in summer leading to retention of winter snow and ice sheet growth. All that remained was to show exactly how the climate system accomplished the necessary links.
  • Changes in storm tracks and energy transports in a warmer climate simulated by the GFDL CM2.1 modelYutian Wu, Mingfang Ting, Richard Seager, Huei-Ping Huang, and Mark A. Cane | Climate Dynamics [+]
    Abstract: Storm tracks play a major role in regulating the precipitation and hydrological cycle in midlatitudes. The changes in the location and amplitude of the storm tracks in response to global warming will have significant impacts on the poleward transport of heat, momentum and moisture and on the hydrological cycle. Recent studies have indicated a poleward shift of the storm tracks and the midlatitude precipitation zone in the warming world that will lead to subtropical drying and higher latitude moistening. This study agrees with this key feature for not only the annual mean but also different seasons and for the zonal mean as well as horizontal structures based on the analysis of Geophysical Fluid Dynamics Laboratory (GFDL) CM2.1 model simulations. Further analyses show that the meridional sensible and latent heat fluxes associated with the storm tracks shift poleward and intensify in both boreal summer and winter in the late twenty-first century (years 2081–2100) relative to the latter half of the twentieth century (years 1961–2000). The maximum dry Eady growth rate is examined to determine the effect of global warming on the time mean state and associated available potential energy for transient growth. The trend in maximum Eady growth rate is generally consistent with the poleward shift and intensification of the storm tracks in the middle latitudes of both hemispheres in both seasons. However, in the lower troposphere in northern winter, increased meridional eddy transfer within the storm tracks is more associated with increased eddy velocity, stronger correlation between eddy velocity and eddy moist static energy, and longer eddy length scale. The changing characteristics of baroclinic instability are, therefore, needed to explain the storm track response as climate warms. Diagnosis of the latitude-by-latitude energy budget for the current and future climate demonstrates how the coupling between radiative and surface heat ?uxes and eddy heat and moisture transport in?uences the midlatitude storm track response to global warming. Through radiative forcing by increased atmospheric carbon dioxide and water vapor, more energy is gained within the tropics and subtropics, while in the middle and high latitudes energy is reduced through increased outgoing terrestrial radiation in the Northern Hemisphere and increased ocean heat uptake in the Southern Hemisphere. This enhanced energy imbalance in the future climate requires larger atmospheric energy transports in the midlatitudes which are partially accomplished by intensi?ed storm tracks. Finally a sequence of cause and effect for the storm track response in the warming world is proposed that combines energy budget constraints with baroclinic instability theory.
  • Changing Frequency and Intensity of Rainfall Extremes over India from 1951 to 2003Chandra Kiran B. Krishnamurthy, Upmanu Lall, Hyun-Han Kwon | Journal of Climate [+]
    Abstract: Using a 1951-2003 gridded daily rainfall dataset for India, the authors assess trends in the intensity and frequency of exceedance of thresholds derived from the 90th and the 99th percentile of daily rainfall. A nonparametric method is used to test for monotonic trends at each location. A field significance test is also applied at the national level to assess whether the individual trends identified could occur by chance in an analysis of the large number of time series analyzed. Statistically significant increasing trends in extremes of rainfall are identified over many parts of India, consistent with the indications from climate change models and the hypothesis that the hydrological cycle will intensify as the planet warms. Specifically, for the exceedance of the 99th percentile of daily rainfall, all locations where a significant increasing trend in frequency of exceedance is identified also exhibit a significant trend in rainfall intensity. However, extreme precipitation frequency over many parts of India also appears to exhibit a decreasing trend, especially for the exceedance of the 90th percentile of daily rainfall. Predominantly increasing trends in the intensity of extreme rainfall are observed for both exceedance thresholds.
  • Climate, Streamflow Prediction and Water Management in northeast Brazil: societal trends ...Broad, K., A. Pfaff, R. Taddei, A. Sankarasubramanian and U. Lall | Climate Change [+]
    Abstract: We assess the potential benefits from innovative forecasts of the stream flows that replenish reservoirs in the semi-arid state of Ceará, Brazil. Such forecasts have many potential applications. In Ceará, they matter for both water-allocation and participatory-governance issues that echo global debates. Our qualitative analysis, based upon extensive fieldwork with farmers, agencies, politicians and other key actors in the water sector, stresses that forecast value changes as a society shifts. In the case of Ceará, current constraints on the use of these forecasts are likely to be reduced by shifts in water demand, water allocation in the agricultural Jaguaribe Valley, participatory processes for water allocation between this valley and the capital city of Fortaleza, and risk perception. Such changes in the water sector can also have major distributional impacts.
  • Climatic precursors of autumn streamflow in the northeast United StatesGavin Gong, Lucien Wang and Upmanu Lall | Climatic precursors of autumn streamflow in the northeast United States [+]
    Abstract: In this study, statistical linkages between autumn streamflow in the northeast United States and preceding summer sea surface temperatures are developed to establish predictive potential for climate-informed seasonal streamflow forecasts in this region. Predictor regions with physically plausible teleconnections to local stream?ow are identified and evaluated in a multivariate and nonlinear framework using local regression techniques. Three such regions are identified, located in the Bering Sea, the tropical Pacific just west of Mexico, and the tropical Atlantic off the coast of Africa. Asymmetries in each region’s univariate local regression result are apparent, and bivariate local regressions are used to attribute these asymmetries to interactions with physical mechanisms associated with the other two regions, and possibly other unaccounted for climatic predictors. A bivariate model including the tropical Paci?c and tropical Atlantic regions yields the strongest local regression result, explaining 0.68 of the interannual streamflow variability. An analogous multivariate linear regression analysis is only able to explain 0.20 of the streamflow variability and thus the use of nonlinear methods’ results in a marked improvement in streamflow simulation capability. Cross-validation considerably weakens the streamflow forecasts using this model; however, forecast skill may improve with a longer period of record or the inclusion of additional predictors.
  • Coordination in the Management of Water Resources: Understanding the Role of Property Rights ...Heikkila, T | Water Policy [+]
    Abstract: This paper considers how water rights laws can shape the ways water providers coordinate when devising conjunctive water management programs. Conjunctive water management is a particularly useful tool for analyzing water management coordination because it involves certain physical and organizational complexities that may facilitate the need for coordination. It takes advantage of the natural storage capacity of underground aquifers for the storage of surface supplies during high flow seasons, allowing for recovery of those supplies when surface flows are limited. This paper compares conjunctive management programs across Arizona, California and Colorado. It identifies the distinct types of coordination associated with conjunctive water management programs across these states and shows that these forms of coordination depend upon the larger institutional setting governing rights to water resources.
  • Current Approaches to Seasonal-to-Interannual Climate PredictionsL. Goddard, S. J. Mason, S. E. Zebiak, C. F. Ropelewski, R. Basher, and M. A. Cane | International Journal of Climatology [+]
    Abstract: This review paper presents an assessment of the current state of knowledge and capability in seasonal climate prediction at the end of the 20th century. The discussion covers the full range of issues involved in climate forecasting, including (1) the theory and empirical evidence for predictability; (2) predictions of surface boundary conditions, such as sea surface temperatures (SSTs) that drive the predictable part of the climate; (3) predictions of the climate; and (4) a brief consideration of the application of climate forecasts. Within this context, the research of the coming decades that seeks to address shortcomings in each area is described.
  • Data Mining and Its Applications for Modeling Rainfall ExtremesD. Nagesh Kumar and C. T. Dhanya | Journal of Hydraulic Engineering [+]
    Abstract: Data mining is a new powerful technology which helps in extracting hidden predictive information (future trends and behaviors) from large databases and thus facilitation decision makers to make proactive, knowledge-driven decisions. In this paper, a brief overview of various data mining functionalities, and an extensive review of the works done on temporal data mining are discussed. Of the two frameworks of temporal data mining, one that of frequent episodes is discussed in detail by explicating the various algorithms developed so far. Also, a case study using one of the algorithms, Minimal Occurrences With Constraints and Time Lags (MOWCATL), for extracting the rules to explain the spatial and temporal variation for extreme events in India is discussed and the results are shown.
  • Data Mining for Evolving Fuzzy Association Rules for Predicting Monsoon Rainfall of IndiaC. T. Dhanya and D. Nagesh Kumar | Journal of Intelligent Systems [+]
    Abstract: We used a data mining algorithm to evolve fuzzy association rules between the atmospheric indices and the Summer Monsoon Rainfall of All-India and two homogenous regions (Peninsular and West central). El Nino and Southern Oscillation (ENSO) and Equatorial Indian Ocean Oscillation zonal wind index (EQWIN) indices are used as the causative variables. Rules extracted are showing a negative relation with ENSO index and a positive relation with the EQWIN index. A fuzzy rule based prediction technique is also implemented on the same indices to predict the summer monsoon rainfall of All-India, Peninsular, and West central regions. Rules are defined using a training dataset for the period 1958-1999 and validated for the period 2000- 2006. The fuzzy outputs of the defined rules are converted into crisp outputs using the weighted counting algorithm. The variability of the summer monsoon rainfall over the years is well captured by this technique, thus proving to be efficient even when the linear statistical relation between the indices is weak.
  • Considerations for conducting incubations to study the mechanisms of As release in reducing ...K. A. Radloff, A. R. Manning, B. Mailloux, Y. Zheng, M. M. Rahman, M. R. Huq, K. M. Ahmed and ... | Applied Geochemistry [+]
    Abstract: Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orangecolored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1x or (4) 10x the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment.
  • Conditional first-order second-moment method and its application to the quantification of ...Kunstmann H., Kinzelbach W., Siegfried T. | Water Resources Research [+]
    Abstract: Decision making in water resources management usually requires the quantification of uncertainties. Monte Carlo techniques are suited for this analysis but imply a huge computational effort. An alternative and computationally efficient approach is the first-order second-moment (FOSM) method which directly propagates parameter uncertainty into the result. We apply the FOSM method to both the groundwater flow and solute transport equations. It is shown how conditioning on the basis of measured heads and/or concentrations yields the “principle of interdependent uncertainty” that correlates the uncertainties of feasible hydraulic conductivities and recharge rates. The method is used to compute the uncertainty of steady state heads and of steady state solute concentrations. It is illustrated by an application to the Palla Road Aquifer in semiarid Botswana, for which the quantification of the uncertainty range of groundwater recharge is of prime interest. The uncertainty bounds obtained by the FOSM method correspond well with the results obtained by the Monte Carlo method. The FOSM method, however, is much more advantageous with respect to computational efficiency. It is shown that at the planned abstraction rate the probability of exceeding the natural replenishment of the Palla Road Aquifer by overpumping is 30%.
  • Climatic Teleconnections Associated with a Western Himalayan River: Melt Period Inflow into the Bhakra Dam in IndiaIndrani Pal, Upmanu Lall, Andrew Robertson, Mark A Cane, and Rajeev Bansal | Submitted to Journal of Hydrology [+]
    Abstract: Understanding the relationship between low frequency variations in large-scale atmospheric circulation driven by the oceans and high latitude hydro-climatic variability at regional scales is important to assess the projections of climate change in these regions, and for designing measures for climate change adaptation. Here we analyze the recent (1978-2004) variability in the melt period river flow into the Bhakra dam in India through correlation and composite analyses of associated large-scale climatic patterns in winter. Bhakra total inflow is a sum of the Satluj River flow and the volume of flow diverted from the Beas River through the Beas Satluj Link (BSL) channel. These flow components are highly correlated with each other. The spring (March-June), melt period inflow of Bhakra dam is very well correlated with the winter precipitation and temperature of the Satluj basin. Spring seasonal inflow anomalies are primarily connected to the winter atmospheric circulation patterns over the Western Himalayas and adjoining north and central Indian plains, which are in turn linked to the fluctuation of equatorial winter Sea Surface Temperature over the western Indian Ocean and the central Pacific Ocean. They also appear to be modulated by the changes in the winter pressure fields over Indonesian Throughflow, the connecting point of Indian and Pacific Oceans. Low spring inflows are associated with negative temperature anomalies over Siberian High and central to eastern Pacific and a negative pressure system over the South-east Asia, Indonesian Seas, eastern Indian Ocean and western Pacific, and a positive pressure system over Iceland and Arctic during winter corresponding to weaker westerlies. On the other hand, a high inflow in spring is linked with a deep low-pressure system and convergence of wind from two opposite directions over the North Atlantic Ocean, and stronger westerlies. Teleconnections of spring Bhakra inflow with the IOD, SOI and Nino climate indices in winter are also noted, such that positive winter IOD and ENSO events (positive pressure field over east Indian Ocean and west Pacific) are related to higher winter precipitation over the Western Himalayas leading to higher spring inflow of Bhakra. These teleconnections provide some promise for improving the long lead prediction capability for inflows into this important multi-purpose reservoir that is operated at seasonal time scales for irrigation, flood control and hydropower production. They also provide '! potential directions for the statistical downscaling of precipitation, temperature and/or streamflow directly from large-scale climate model simulations of ocean temperature and atmospheric pressure fields.
  • Closing of the Indonesian seaway as a precursor to east African aridification around 3-4 million ...Mark A. Cane and Peter Molnar | Nature [+]
    Abstract: Global climate change around 3±4 Myr ago is thought to have influenced the evolution of hominids, via the aridification of Africa, and may have been the precursor to Pleistocene glaciation about 2.75 Myr ago. Most explanations of these climatic events involve changes in circulation of the North Atlantic Ocean due to the closing of the Isthmus of Panama. Here we suggest, instead, that closure of the Indonesian seaway 3±4 Myr ago could be responsible for these climate changes, in particular the aridification of Africa. We use simple theory and results from an ocean circulation model to show that the northward displacement of New Guinea, about 5 Myr ago, may have switched the source of flow through Indonesia from warm South Pacific to relatively cold North Pacific waters. This would have decreased sea surface temperatures in the Indian Ocean, leading to reduced rainfall over eastern Africa. We further suggest that the changes in the equatorial Pacific may have reduced atmospheric heat transport from the tropics to higher latitudes, stimulating global cooling and the eventual growth of ice sheets.
  • Collaboration and Institutional Endurance in U.S. Water PolicyAndrea K. Gerlak and Tanya Heikkila | Political Science and Politics [+]
    Abstract: Collaborative institutions, which involve the collective decision-making by multiple political agencies, communities, and stakeholders, are becoming increasingly important for addressing policy dilemmas that are not bound within a single jurisdiction. This is especially true in the environmental arena (Wondolleck and Yaffee 2000; Karkkainen 2002; Koontz et al. 2004; Lubell 2004; McKinney and Harmon 2004; Brick et al. 2001; Sabel et al. 2000). In the water management field, for instance, Sabatier, Weible, and Ficker (2005) have argued that the growth of collaborative efforts among small watersheds is so widespread that it has become a new paradigm of management. A considerable body of policy research, particularly on watershed management, has begun to examine the factors that support the emergence of collaborative environmental governance (Lubell et al. 2002; Blomquist 1992; Ostrom 1990). Understanding what factors affect the performance of collaborative institutions has also become an emerging theme in this scholarship (Sabatier, Leach, Lubell, and Pelkey 2005; Leach, Pelkey, and Sabatier 2002; Conley and Moote 2003; Innes and Booher 1999). Empirically and methodologically however, what is often missing from research on collaborative institutions is a clearer picture of what factors support the endurance of collaborative institutions over time. Institutional endurance, at a basic level, can be defined as the capacity of an institutional arrangement to persist over time. Here we are concerned not with the endurance of institutions broadly conceived, but rather with the endurance of collaborative institutions and those mechanisms that keep collaborative actors at the table and working together. We suggest that many of the factors that bring actors together in the first place are also those that keep them together. Yet, as a wide body of literature on institutions and collaboration suggests, the role of learning and adaptation over time also plays a critical role in this process. To help illuminate how this theory can be supported, this paper introduces examples from four largescale collaborative watershed management programs in the U.S., including efforts along the Columbia River and Sacramento-San Joaquin Rivers, and in the Chesapeake Bay and Florida Everglades. In concluding, we discuss the role of endurance in assessing the performance of collaborative watershed management institutions.
  • Compliance and Performance in International Water Agreements: The Case of the Naryn/Syr Darya BasinThomas Bernauer and Tobias Siegfried | Global Governance [+]
    Abstract: Many case studies and some large-N research have shown that upstreamdownstream cooperation in international river basins occurs quite frequently. The same holds for global water governance efforts more generally. Yet such findings are blind in one eye because they focus primarily on political commitments or compliance with international agreements. A policy performance metric (PER) allows for a more substantive assessment of success or failure in international water governance. To test its usefulness, this article applies this metric to the Naryn/Syr Darya basin, a major international river system in Central Asia. Management of the Toktogul reservoir, the main reservoir in the Naryn/Syr Darya basin, was internationalized in 1991 when the Soviet Union collapsed. Compliance with an international agreement, concluded in 1998, has been quite high. This agreement establishes an international trade-off between water releases for upstream hydropower production in winter and water releases for downstream irrigation in summer. However, performance of this agreement over time has been very low and highly variable. The management system in place is therefore in urgent need of reform. Studies of international and global water governance should pay more attention to the degree to which political commitments actually further de facto problem solving.
  • Bayesian dynamic modeling for monthly Indian summer monsoon rainfall using ENSO and EQUINOORajib Maity and D. Nagesh Kumar | Journal of Geophysical Research [+]
    Abstract: There is an established evidence of climatic teleconnection between El Nin˜ o – Southern Oscillation (ENSO) and Indian summer monsoon rainfall (ISMR) during June through September. Against the long-recognized negative correlation between ISMR and ENSO, unusual experiences of some recent years motivate the search for some other causal climatic variable, influencing the rainfall over the Indian subcontinent. Influence of recently identified Equatorial Indian Ocean Oscillation (EQUINOO, atmospheric part of Indian Ocean Dipole mode) is being investigated in this regard. However, the dynamic nature of cause-effect relationship burdens a robust and consistent prediction. In this study, (1) a Bayesian dynamic linear model (BDLM) is proposed to capture the dynamic relationship between large-scale circulation indices and monthly variation of ISMR and (2) EQUINOO is used along with ENSO information to establish their concurrent effect on monthly variation of ISMR. This large-scale circulation information is used in the form of corresponding indices as exogenous input to BDLM, to predict the monthly ISMR. It is shown that the Indian monthly rainfall can be modeled in a better way using these two climatic variables concurrently (correlation coefficient between observed and predicted rainfall is 0.82), especially in those years when negative correlation between ENSO and ISMR is not well reflected (i.e., 1997, 2002, etc.). Apart from the efficacy of capturing the dynamic relationship by BDLM, this study further establishes that monthly variation of ISMR is influenced by the concurrent effects of ENSO and EQUINOO.
  • Atmospheric GCM Response to Extratropical SST Anomalies: Synthesis and EvaluationY. Kushnir, W. A. Robinson, I. Bladé, N. M. J. Hall, S. Peng, and R. Sutton | Journal of Climate [+]
    Abstract: We examine the advances in our understanding of extratropical atmosphere-ocean interaction over the past decade and a half, focusing on the atmospheric response to sea surface temperature anomalies. The main goal of the paper is to assess what was learned from general circulation model (GCM) experiments over the recent two decades or so. Observational evidence regarding the nature of the interaction and dynamical theory of atmospheric anomalies forced by surface thermal anomalies are reviewed. We then proceed to examine three types of GCM experiments used to address this problem: models with fixed climatological conditions and idealized, stationary SST anomalies; models with seasonally evolving climatology forced with realistic, time-varying SST anomalies; and models coupled to an interactive ocean. From representative recent studies, we argue that the extratropical atmosphere does respond to changes in underlying SST although the response is small compared to internal (unforced) variability. Two types of interactions govern the response: One is an eddy-mediated process, in which a baroclinic response to thermal forcing induces and combines with changes in the position or strength of the storm tracks. This process can lead to an equivalent barotropic response that feeds back positively on the ocean mixed layer temperature. The other is a linear, thermodynamic interaction in which an equivalent-barotropic low-frequency atmospheric anomaly forces a change in SST and then experiences reduced surface thermal damping due to the SST adjustment. Both processes contribute to an increase in variance and persistence of low-frequency atmospheric anomalies and, in fact, may act together in the natural system.
  • A stochastic nonparametric technique for space-time disaggregation of streamflowsPrairie J., B. Rajagopalan, U. Lall, T. Fulp | Water Resources Research [+]
    Abstract: Stochastic disaggregation models are used to simulate streamflows at multiple sites preserving their temporal and spatial dependencies. Traditional approaches to this problem involve transforming the streamflow data of each month and at every location to a Gaussian structure and subsequently fitting a linear model in the transformed space. The simulations are then back transformed to the original space. The main drawbacks of this approach are (1) transforming marginals to Gaussian need not lead to the correct multivariate distribution particularly if the dependence across variables is nonlinear, and (2) the number of parameters to be estimated for a traditional disaggregation model grows rapidly with an increase in space or time components. We present a K-nearest-neighbor approach to resample monthly flows conditioned on an annual value in a temporal disaggregation or multiple upstream locations conditioned on a downstream location for a spatial disaggregation. The method is parsimonious, as the only parameter to estimate is K (the number of nearest neighbors to be used in resampling). Simulating space-time flow scenarios conditioned upon large-scale climate information (e.g., El Niño–Southern Oscillation, etc.) can be easily achieved. We demonstrate the utility of this methodology by applying it for space-time disaggregation of streamflows in the Upper Colorado River basin. The method appropriately captures the distributional and spatial dependency properties at all the locations.
  • A Streamflow Forecasting Framework Using Multiple Climate and Hydrological ModelsPaul J. Block, Francisco Assis Souza Filho, Liqiang Sun, and Hyun-Han Kwon | Journal of the American Water Resources Association [+]
    Abstract: Water resources planning and management ef?cacy is subject to capturing inherent uncertainties stemming from climatic and hydrological inputs and models. Stream?ow forecasts, critical in reservoir operation and water allocation decision making, fundamentally contain uncertainties arising from assumed initial conditions, model structure, and modeled processes. Accounting for these propagating uncertainties remains a formidable challenge. Recent enhancements in climate forecasting skill and hydrological modeling serve as an impetus for further pursuing models and model combinations capable of delivering improved stream?ow forecasts. However, little consideration has been given to methodologies that include coupling both multiple climate and multiple hydrological models, increasing the pool of stream?ow forecast ensemble members and accounting for cumulative sources of uncertainty. The framework presented here proposes integration and of?ine coupling of global climate models (GCMs), multiple regional climate models, and numerous water balance models to improve stream?ow forecasting through generation of ensemble forecasts. For demonstration purposes, the framework is imposed on the Jaguaribe basin in northeastern Brazil for a hindcast of 1974-1996 monthly stream?ow. The ECHAM 4.5 and the NCEP?MRF9 GCMs and regional models, including dynamical and statistical models, are integrated with the ABCD and Soil Moisture Accounting Procedure water balance models. Precipitation hindcasts from the GCMs are downscaled via the regional models and fed into the water balance models, producing stream?ow hindcasts. Multi-model ensemble combination techniques include pooling, linear regression weighting, and a kernel density estimator to evaluate stream?ow hindcasts; the latter technique exhibits superior skill compared with any single coupled model ensemble hindcast.
  • A Synthesis of Information on Rapid Land-cover Change for the Period 1981-2000Lepers E., E. F. Lambin, A. C. Janetos, R. DeFries, F. Achard, N. Ramankutty, and R. J. Scholes | BioScience [+]
    Abstract: This article presents a synthesis of what is known about areas of rapid land-cover change around the world over the past two decades, based on data compiled from remote sensing and censuses, as well as expert opinion. Asia currently has the greatest concentration of areas of rapid land-cover changes, and dryland degradation in particular. The Amazon basin remains a major hotspot of tropical deforestation. Rapid cropland increase, often associated with large-scale deforestation, is prominent in Southeast Asia. Forest degradation in Siberia, mostly related to logging activities, is increasing rapidly. The southeastern United States and eastern China are experiencing rapid cropland decrease. Existing data do not support the claim that the African Sahel is a desertification hotspot. Many of the most populated and rapidly changing cities are found in the tropics.
  • Accelerated simulation of passive tracers in ocean circulation modelsSamar Khatiwala, Martin Visbeck, and Mark A. Cane | Ocean Modelling [+]
    Abstract: A novel strategy is proposed for the efficient simulation of geochemical tracers in ocean models. The method captures the tracer advection and diffusion in a general circulation model (GCM) without any alteration (or even knowledge) of the GCM code. In comparison with offine tracer models, the proposed method is considerably more efficient and automatically includes all parameterizations of unresolved processes present in the most sophisticated GCMs. A comparison with a global configuration of the MIT GCM shows that the scheme can capture the complex three-dimensional transport of a state-of-the-art GCM. A key advantage of the proposed technique is the ability to directly compute steady-state solutions, a facility particularly well-suited to tracers such as natural radiocarbon. This capability is applied to develop a novel algorithm for accelerating the dynamical adjustment of ocean models.
  • A simple mechanism for a complex aquiferStergios Athanassoglou, Glenn Sheriff, Tobias Siegfried, and Woonghee Tim Huh | Working Paper [+]
    Abstract: Standard economic models of groundwater management assume perfect transmissivity (i.e., the aquifer behaves as a bathtub), no external eff ects of groundwater stocks, and/or homogenous agents. In this article, we develop a model relaxing these assumptions. Although our model generalizes to an arbitrary number of cells, we are able to obtain key insights with a two-cell nite-horizon di fferential game. We need a simple linear mechanism that induces the socially optimal extraction path in Markov-perfect equilibrium. Moreover, implementation requires that the regulator need only monitor the state of the resource (groundwater elevation), not individual extraction rates. We illustrate the mechanism with a simulation based on data from the Indian state of Andhra Pradesh. The simulation suggests that notable welfare loss may occur if the regulator disregards physical and economic complexity.
  • A Simple Framework for Incorporating Seasonal Streamflow Forecasts Into Exist. Wat. Res. ManagementGavin Gong, Lucien Wang, Laura Condon, Alastair Shearman, and Upmanu Lall | Journal of the American Water Resources Association [+]
    Abstract: Climate-based stream?ow forecasting, coupled with an adaptive reservoir operation policy, can potentially improve decisions by water suppliers and watershed stakeholders. However, water suppliers are often wary of straying too far from their current management practices, and prefer forecasts that can be incorporated into existing system modeling tools. This paper presents a simple framework for utilizing stream?ow forecasts that works within an existing management structure. Climate predictors are used to develop seasonal in?ow forecasts. These are used to specify operating rules that connect to the probability of future (end of season) reservoir states, rather than to the current storage, as is done now. By considering both current storage and anticipated in?ow, the likelihood of meeting management goals can be improved. The upper Delaware River Basin in the northeastern United States is used to demonstrate the basic idea. Physically plausible climatebased forecasts of March-April reservoir in?ow are developed. Existing simulation tools and rule curves for the system are used to convert the in?ow forecasts to reservoir level forecasts. Operating policies are revised during the forecast period to release less water during forecasts of low reservoir level. Hindcast simulations demonstrate reductions of 1.6% in the number of drought emergency days, which is a key performance measure. Forecasts with different levels of skill are examined to explore their utility.
  • A hydrologically driven model of swamp water mosquito population dynamicsJeffrey Shaman, Marc Spiegelman, Mark Cane, and Marc Stieglitz | Ecological Modelling [+]
    Abstract: We develop a swamp water mosquito population model that is forced solely by environmental variability. Measured temperature and land surface wetness conditions are used to simulate Anopheles walkeri population dynamics in a northern New Jersey habitat. Land surface wetness conditions, which represent oviposition habitat availability, are derived from simulations using a dynamic hydrology model. Using only these two density-independent effects, population model simulations of biting Anoph. walkeri correlate signi?cantly with light trap collections. These results suggest that prediction of mosquito populations and the diseases they transmit could be better constrained by inclusion of environmental variability.
  • A Local Forecast of Land Surface Wetness Conditions Derived from Seasonal Climate PredictionsJeffrey Shaman, Marc Stieglitz, Stephen Zebiak, and Mark Cane | Journal of Hydrometeorology [+]
    Abstract: An ensemble local hydrologic forecast derived from the seasonal forecasts of the International Research Institute for Climate Prediction (IRI) is presented. Three-month seasonal forecasts were used to resample historical meteorological conditions and generate ensemble forcing datasets for a TOPMODEL-based hydrology model. Eleven retrospective forecasts were run at Florida and New York sites. Forecast skill was assessed for mean area modeled water table depth (WTD) and compared with WTD simulated with observed data. Hydrology model forecast skill was evident at the Florida site. Persistence of initial hydrologic conditions and local skill of the IRI seasonal forecast contributed to this local hydrologic forecast skill. At the New York site, there was no persistence of initial hydrologic conditions and local skill of the IRI seasonal forecast was poor; these factors precluded local hydrologic forecast skill at this site.
  • A multiobjective discrete stochastic optimization approach to shared aquifer management ...Siegfried, T., and W. Kinzelbach | Water Resources Research [+]
    Abstract: Negative effects from groundwater mining are observed globally. They threaten future supply locally. Especially in semiarid to arid regions, where aquifers are the sole freshwater resource, this is problematic and can lead to an excessive rise of provision costs. Proper resource management in such environments is crucial. In many instances, however, aquifers are common property resources. In such cases and depending on resource characteristics and the nature of competing uses, their management is inherently multiobjective, and benefits from cooperative management are likely to be substantial. This paper presents a methodology for the determination of optimal, cooperative allocation policies in multiobjective aquifer management problems. Our model couples a finite difference aquifer model with an economic model that accounts for water provision costs. Discounted temporal installation and pumping and conveyance costs determine the vector-valued objective function. Each of the objectives characterizes the individual present costs over a given time horizon that the corresponding decision makers wish to minimize. Constraint handling is implemented by the option of moving wells. A multiobjective evolutionary algorithm is coupled to the management model so as to approximate cooperative tradeoff policies on the Pareto surface. These solutions can be ranked against existing, noncooperative status quo strategies. Consequently, the simulation-optimization model is applied to the northwest Sahara aquifer system which is used noncooperatively as a resource by Algeria, Tunisia, and Libya. We find that significant capital gains can be achieved by the establishment of intelligent pump scheduling. Since each country could benefit, a strong incentive toward the implementation of such cooperative strategies exists.
  • A role for ocean biota in tropical intraseasonal atmospheric variabilityHezi Gildor, Adam H. Sobel, Mark A. Cane, and Raymond N. Sambrotto | Geophysical Research Letters [+]
    Abstract: We propose that temporal variations within the marine plankton system can induce intraseasonal variations in sea surface temperature (SST) through the effect on solar penetration due to chlorophyll and other optically active organic components. Sensitivity studies with a simple model suggest that these small oscillations in SST may stimulate radiative-convective oscillations in the atmosphere which amplify them and thus induce or modulate significant variability in the coupled system. Long term bio-optical measurements in the Western Pacific, where satellite time series are degraded by clouds, would provide a test of our theory and would improve our understanding of the heat balance in this climatically important region.
  • Agricultural Water Management and Climate Risk: Report to the Bill and Melinda Gates FoundationCasey Brown and James Hansen | The International Research Institute for Climate and Society [+]
    Abstract: Exposure to a high degree of climate risk is a characteristic feature of rainfed agriculture in the drylands of sub-Saharan Africa and parts of South Asia. A growing body of evidence links unmitigated hydroclimatic variability to poor economic growth in developing countries. At a more local level, climate exerts a profound influence on the lives of poor rural populations who depend on agriculture for livelihood and sustenance, who are unprotected against climate-related diseases, who lack secure access to water and food, and who are vulnerable to hydrometeorological hazard. Several mechanisms by which climate risk impacts rural households combine with other factors to trap rural populations in chronic poverty. Climate change is expected to intensify many of the challenges facing dryland agriculture in Africa and South Asia, but in ways that can only be partially anticipated. Improved control of water resources is a fundamental method for mitigating the impacts of climate variability. Methods range from small scale on-farm and community based measures with local control to large scale infrastructure with institutionalized and governmental control. There are tradeoffs inherent in any selection of water management approaches at any scale. One commonly overlooked tradeoff is the relationship between scale and reliability, where reliability of water supply decreases as the scale of water management intervention decreases. African countries and parts of India lack public or private infrastructure to provide storage to mitigate the variability of rainfall. The investments in agricultural water management that are viable for dryland agriculture in Africa in the foreseeable future provide only partial control and leave substantial residual risk. The infeasibility of achieving a high level of water control across the vast dryland farming regions of Africa in the near to medium term, and increasing stress on groundwater and surface water resources in much of India point to the need to exploit every opportunity to deal with the residual climate risk that water control systems alone cannot mitigate. We introduce the concept of residual risk to communicate the limitations of agricultural water management (or any singular approach) for managing climate risk and to facilitate the consideration of unmanaged climate risk. Managing that residual risk in dryland agriculture calls for several investments in parallel with improving agricultural water management. Opportunities include crop germplasm improvement, livelihood diversification, rural climate information systems, financial risk transfer and improved hazard early warning and response. We propose three specific areas of investment that we consider timely and promising. Each targets a different layer of risk: (a) climate-informed investment in water management to increase the resilience of agricultural development and stimulate investment; (b) rural climate information services to support adaptive management of water and production activities, as a way to manage residual risk with incomplete water control; and (c) integrated, multi-hazard (drought-flood-food insecurity) early warning systems to support more timely and better coordinated response to climatic shocks that exceed the coping capacity of rural communities.
  • Amazonia revealed: forest degradation and loss of ecosystem goods and services in the Amazon BasinJ. A. Foley, G. P. Asner, M. H. Costa, M. T. Coe, R. DeFries, H. K. Gibbs, E. A. Howard, S. Olson | The Ecological Society of America [+]
    Abstract: The Amazon Basin is one of the world's most important bioregions, harboring a rich array of plant and animal species and offering a wealth of goods and services to society. For years, ecological science has shown how large scale forest clearings cause declines in biodiversity and the availability of forest products. Yet some important changes in the rainforests, and in the ecosystem services they provide, have been underappreciated until recently. Emerging research indicates that land use in the Amazon goes far beyond clearing large areas of forest; selective logging and other canopy damage is much more pervasive than once believed. Deforestation causes collateral damage to the surrounding forests - through enhanced drying of the forest floor, increased frequency of fires, and lowered productivity. The loss of healthy forests can degrade key ecosystem services, such as carbon storage in biomass and soils, the regulation of water balance and river flow, the modulation of regional climate patterns, and the amelioration of infectious diseases. We review these newly revealed changes in the Amazon rainforests and the ecosystem services that they provide.
  • Analysis of Climatic States and Atmospheric Circulation Patterns That Influence Québec Spring ...Oli G. B. Sveinsson; Upmanu Lall; Jocelyn Gaudet; Yochanan Kushnir; Steve Zebiak; and Vincent Fortin | Journal of Hydrologic Engineering [+]
    Abstract: Results from diagnostic analyses to understand the seasonal evolution of the large-scale climatic state responsible for the development and melt of the winter snowpack, and spring–early summer precipitation in the Churchill Falls region on the QuébecLabrador Peninsula, Canada, are presented in the context of the development of an empirical model for seasonal to annual stream?ow forecasting, with a special emphasis on the May–July spring freshet. Teleconnection indices and gridded global measures of atmospheric circulation inferred from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis are used as climatic indicators. Composite and correlation analyses are applied to the climatic indicators conditioned on the spring stream?ow for identi?cation of potential predictors. Meridional and zonal atmospheric ?uxes over the Atlantic and the Paci?c Oceans emanating from regionally persistent sea surface temperature/sea level pressure modes are identi?ed as potential carriers of information. We speculate on the ocean-atmosphere and regional hydrologic mechanisms that may be involved in lending multiseasonal predictability to stream?ows in the region.
  • Analysis of Extreme Summer Rainfall Using Climate Teleconnections and Typhoon Characteristics in ...Hyun-Han Kwon, Abedalrazq F. Khalil, and Tobias Siegfried | Journal of the American Water Resources Association [+]
    Abstract: It is now widely acknowledged that climate variability modulates the frequency of extreme hydrological events. Traditional methodologies for hydrologic frequency analysis are not devised to account for variation in the exogenous teleconnections. Flood frequency analysis is further plagued by the assumptions of stationary in the causal structure as well as ergodicity. Here, we propose a dynamical hierarchical Bayesian analysis to account for exogenous forcing that govern the summer season rainfall. The precursors for Korean summer rainfall at different frequencies are identified utilizing wavelet and independent component analyses. The sea surface temperatures, the ensemble of rainfall predictions by General Circulation Model, in addition to the typhoon attributes were found to have direct correlation with extreme rainfall events and were used as inputs to the logistic regression model. The model parameters are estimated using Markov Chain Monte Carlo and the resulting posterior distributions associated with individual inputs are analyzed to advance our understanding of the spatiotemporal impact of the teleconnections. Eight rainfall stations throughout Korea are considered in this analysis. We demonstrate that the probability of occurrence of extreme events could be successfully projected at a 90% rate of correct classification of extreme events.
  • Annual hydroclimatology of the United StatesA. Sankarasubramanian and Richard M. Vogel | Water Resources Research [+]
    Abstract: An overview of the annual hydroclimatology of the United States is provided. Time series of monthly streamflow, temperature, and precipitation are developed for 1337 watersheds in the United States. This unique data set is then used to evaluate several approaches for estimating the long-term water balance and the interannual variability of streamflow. Traditional relationships which predict either actual evapotranspiration or the interannual variability of streamflow from an aridity index f ¼ PE=P are shown to perform poorly for basins with low soil moisture storage capacity. A water balance model is used to formulate new relationships for predicting actual evapotranspiration and the interannual variability of streamflow. These relationships depend on both the aridity index f ¼ PE=P and a new soil moisture storage index. A physically based approach for estimating the soil moisture storage index is introduced which requires monthly time series of precipitation, potential evapotranspiration, and an estimate of maximum soil moisture holding capacity. The net results are improved expressions for the long-term water balance and the interannual variability of streamflow which do not require either calibration or streamflow data
  • Atmospheric circulation anomalies during two persistent north american droughts: 1932-1939 and ...Benjamin I. Cook, Richard Seager, and Ron L. Miller | Climate Dynamics [+]
    Abstract: We use an early twentieth century (1908–1958) atmospheric reanalysis, based on assimilation of surface and sea level pressure observations, to contrast atmospheric circulation during two periods of persistent drought in North America: 1932–1939 (the ‘Dust Bowl’) and 1948– 1957. Primary forcing for both droughts is believed to come from anomalous sea surface temperatures (SSTs): a warm Atlantic and a cool eastern tropical Pacific. For boreal winter (October–March) in the 1950s, a stationary wave pattern originating from the tropical Pacific is present, with positive centers over the north Pacific and north Atlantic ocean basins and a negative center positioned over northwest North America and the tropical/subtropical Pacific. This wave train is largely absent for the 1930s drought; boreal winter height anomalies are organized much more zonally, with positive heights extending across northern North America. For boreal summer (April–September) during the 1930s, a strong upper level ridge is centered over the Great Plains; this feature is absent during the 1950s and appears to be linked to a weakening of the Great Plains low-level jet (GPLLJ). Subsidence anomalies are co-located over the centers of each drought: in the central Great Plains for the 1930s and in a band extending from the southwest to the southeastern United States for the 1950s. The location and intensity of this subsidence during the 1948–1957 drought is a typical response to a cold eastern tropical Pacific, but for 1932–1939 deviates in terms of the expected intensity, location, and spatial extent. Overall, circulation anomalies during the 1950s drought appear consistent with the expected response to the observed SST forcing. This is not the case for the 1930s, implying some other causal factor may be needed to explain the Dust Bowl drought anomalies. In addition to SST forcing, the 1930s were also characterized by massive alterations to the land surface, including regional-scale devegetation from crop failures and intensive wind erosion and dust storms. Incorporation of these land surface factors into a general circulation model greatly improves the simulation of precipitation and subsidence anomalies during this drought, relative to simulations with SST forcing alone. Even with additional forcing from the land surface, however, the model still has difficulty reproducing some of the other circulation anomalies, including weakening of the GPLLJ and strengthening of the upper level ridge during AMJJAS. This may be due to either weaknesses in the model or uncertainties in the boundary condition estimates. Still, analysis of the circulation anomalies supports the conclusion of an earlier paper (Cook et al. in Proc Natl Acad Sci 106:4997, 2009), demonstrating that land degradation factors are consistent with the anomalous nature of the Dust Bowl drought.
  • Análise Temporal e regioinal de Cheias Anuais por Meio de um Modelo Hierárquico BayesianoCarlos Henrique Ribeiro Lima; Upmanu Lall | XVIII Simpósio Brasileiro de Recursos Hídricos [+]
    Abstract: Flood events have caused several life losses and material damages. In order to better understand the spatial scaling of floods and to predict the statistics associated with flood events, researchers have studied and developed theories about the streamflow scaling with respect to the drainage area. Under global climate change scenarios, it is imperative that one understands the temporal variability of this scaling process and how climate forcings contribute to this variability. Here we estimate the scaling parameters of annual maximum series through a hierarchical Bayesian model, which allow us to reduce the estimate uncertainties. One estimates the intercept and slope of the log-log scaling law of streamflow on area for each year of the historical record of 44 streamflow sites across Brazil, whose catchment areas range from 2588 to 823555 km^2. The results show the inter-annual variability and non-stationarity of the scaling parameters. Simulations of annual maxima for out-of-sample stations agree well with the observed data. Hence, we obtained a model that is able to reproduce series of annual maximum at ungauged sites, opening the path to simulate flood events at those sites under global climate changes.
  • An Orbitally Driven Tropical Source for Abrupt Climate ChangeAmy C. Clement, Mark A. Cane, and Richard Seager | Journal of Climate [+]
    Abstract: Paleoclimatic records from high and low latitudes reveal that the climate has undergone abrupt changes in the past that can occur within decades (see Clark et al. 1999). There is no obvious external forcing of the climate that is so rapid. Abrupt changes therefore must arise from processes internal to the climate system or be the result of a rapid response to a gradual external forcing. Identifying the mechanisms that allow changes to be abrupt is essential for understanding the fundamental behavior of the climate and its sensitivity to forcing. The Younger Dryas (YD), a rapid return to near-glacial conditions lasting nearly a millennium during the last deglaciation, is an example of abrupt climate change. A common explanation for the YD is that meltwater pulses from the retreating Laurentide ice sheet flooded the North Atlantic with freshwater, which led to an abrupt shutdown (or weakening) of deep water formation, cooling the North Atlantic region, and explaining the return to near-glacial conditions in various oceanic and terrestrial climate proxies there (see Alley and Clark 1999). High-resolution records show that the onset and termination of this event occurred within decades (Alley et al. 1993).
  • Amplification of the North American 'Dust Bowl' drought through human-induced land degradationBenjamin I. Cook, Ron L. Miller, and Richard Seager | Proceedings of the National Academy of Sciences [+]
    Abstract: The ‘‘Dust Bowl’’ drought of the 1930s was highly unusual for North America, deviating from the typical pattern forced by ‘‘La Nina’’ with the maximum drying in the central and northern Plains, warm temperature anomalies across almost the entire continent, and widespread dust storms. General circulation models (GCMs), forced by sea surface temperatures (SSTs) from the 1930s, produce a drought, but one that is centered in southwestern North America and without the warming centered in the middle of the continent. Here, we show that the inclusion of forcing from human land degradation during the period, in addition to the anomalous SSTs, is necessary to reproduce the anomalous features of the Dust Bowl drought. The degradation over the Great Plains is represented in the GCM as a reduction in vegetation cover and the addition of a soil dust aerosol source, both consequences of crop failure. As a result of land surface feedbacks, the simulation of the drought is much improved when the new dust aerosol and vegetation boundary conditions are included. Vegetation reductions explain the high temperature anomaly over the northern U.S., and the dust aerosols intensify the drought and move it northward of the purely oceanforced drought pattern. When both factors are included in the model simulations, the precipitation and temperature anomalies are of similar magnitude and in a similar location compared with the observations. Human-induced land degradation is likely to have not only contributed to the dust storms of the 1930s but also ampli?ed the drought, and these together turned a modest SSTforced drought into one of the worst environmental disasters the U.S. has experienced.
  • An Assessment of Investments in Agricultural and Transportation Infrastructure, Energy, and ...Paul J. Block, Ph.D. | CGIAR Challenge Program on Water and Food [+]
    Abstract: Ethiopia is at a critical crossroads with a burgeoning population, a severely depressed national economy, insufficient agricultural production, and a minimal number of developed energy sources. This study assesses how investment in and management of water resources, together with related policy reforms, may mitigate the negative effects of hydrologic variability on the performance and structure of the Ethiopian economy. This is accomplished by identifying interventions both aimed at managing hydrologic variability, and at decreasing the vulnerability of the economy to potential shocks. The areas of focus include increased infrastructure for agricultural irrigation and roads, large-scale hydropower generation, and a precipitation forecast model. A dynamic climate agro-economic model of Ethiopia is utilized to assess irrigation and road construction investment strategies in comparison to a baseline scenario over a 12-year time horizon. Although both investments create positive economic boosts, the irrigation investment, on average, slightly outperforms the road investment, producing an average GDP growth rate of 0.95% versus 0.75% over the baseline scenario, along with lower associated poverty and malnutrition rates. The benefit-cost (b-c) ratios for the projects also favor the irrigation investment. The upper Blue nile basin harbors considerable untapped potential for irrigation and large-scale hydropower development and expansion. An integrated model is employed to assess potential conditions based on hydrologic variability and streamflow policies. The model indicates that large-scale development typically produces b-c ratios from 1.6- 2.1 under historical climate regimes for the projects specified. Climate change scenarios indicate potential for small b-c increases, but reflect possible significant decreases. stochastic modeling of scenarios representing a doubling of the historical frequency of El niño events indicates b-c ratios as low as 1.0 due to a lack of timely water. An evaluation of expected energy growth rates reinforces the need for significant economic planning and the necessity of securing energy trade contracts prior to extensive development. A Ramsey growth model for energy development specifies project multipliers on total GDP over the 100-year simulation ranging from 1.7-5.2, for various climatologic conditions. The Blue Nile basin also holds possibility for improvement in rain-fed agricultural production through precipitation forecasting. one-season lead predictors for forecasting of the Kiremt season precipitation are identified from the large scale ocean-atmosphereland system. This forecast is of tremendous value, giving farmers crucial indication of potential future climatic conditions, and is a solid improvement over climatology, as currently utilized by the Ethiopian national Meteorological Institute. Using crop yield potential from the 1961-2000 period and general seed costs, farmers basing cropping decisions on the forecast model, in lieu of climatology, would have experienced superior net incomes.
  • An Ensemble Seasonal Forecast of Human Cases of St. Louis Encephalitis in Florida Based on ...Jeffrey Shaman, Jonathan F. Day, Marc Stieglitz, Stephen Zebiak, and Mark Cane | Climatic Change [+]
    Abstract: We present a method for the ensemble seasonal prediction of human St. Louis encephalitis (SLE) incidence and SLE virus transmission in Florida. We combine empirical relationships between modeled land surface wetness and the incidence of human clinical cases of SLE and modeled land surface wetness and the occurrence of SLE virus transmission throughout south Florida with a previously developed method for generating ensemble, seasonal hydrologic forecasts. Retrospective seasonal forecasts of human SLE incidence are made for Indian River County, Florida, and forecast skill is demonstrated for 2–4 months. A sample seasonal forecast of human SLE incidence is presented. This study establishes the skill of a potential component of an operational SLE forecast system in south Florida, one that provides information well in advance of transmission and may enable early interventions that reduce transmission. Future development of this method and operational application of these forecasts are discussed. The methodology also will be applied to West Nile virus monitoring and forecasting.
  • Decadal upper ocean temperature variability in the tropical PacificWilco Hazeleger, Martin Visbeck, Mark Cane, Alicia Karspeck, and Naomi Naik | Journal of Geophysical Research [+]
    Abstract: Decadal variability in upper ocean temperature in the Pacific is studied using observations and results from model experiments Especially propagation of upper ocean thermal anomalies from the midlatitudes to the tropics is studied as a possible source for decadal equatorial thermocline variability In the observations propagation along the subtropical gyre of the North Pacific is clear However no propagation into the equatorial region is found Model experiments with an ocean model forced with observed monthly wind and wind stress anomalies are performed to study the apparent propagation Distinct propagation of thermal anomalies in the subtropics is found in the model although the amplitude of the anomalies is small The anomalies clearly propagate into the tropics but they do not reach the equatorial region The small response at the equator to extratropical variability consists of a change in the mean depth of the thermocline It appears that most variability in the subtropics and tropics is generated by local wind stress anomalies The results are discussed using results from a linear shallow water model in which similar features are found.
  • Demand management of groundwater with monsoon forecastingBrown, C ., P. Rogers, U. Lall | Agricultural Systems [+]
    Abstract: This paper presents an operational approach to setting prices for groundwater in accordance with the interannual variability of monsoon rainfall and the dynamic cost of groundwater use to society. The pricing system is designed for the state of Tamil Nadu, India, where groundwater is largely unregulated and the electricity for pumping is heavily subsidized. Depletion of aquifers during the primary growing season causes environmental damage and drying of wells. The proposed price-setting system estimates the marginal social cost of groundwater use based on the current state of aquifer storage and the forecast of the coming monsoon. Prices are set prior to onset of the monsoon so farmers can plan crop rotations according to the expectation of seasonal rainfall as reflected in the pricing signal. During years that forecasts accurately characterize the probability distribution of monsoon outcomes the market signal encourages economically efficient use of the resource. When monsoons differ from the expected outcome farmers are cushioned by ancillary effects of the pricing system.
  • Modified Support Vector Machine Based Prediction Model on Streamflow at the Shihmen Reservoir, TaiwanPei-Hao Li, Hyun-Han Kwon, Liqiang Sun, Upmanu Lall and Jehng-Jung Kao | International Journal of Climatology [+]
    Abstract: The uncertainty of the availability of water resources during the boreal winter has led to signi?cant economic losses in recent years in Taiwan. A modified support vector machine (SVM) based prediction framework is thus proposed to improve the predictability of the inflow to Shihmen reservoir in December and January, using climate data from the prior period. Highly correlated climate precursors are first identified and adopted to predict water availability in North Taiwan. A genetic algorithm based parameter determination procedure is implemented to the SVM parameters to learn the non-linear pattern underlying climate systems more ?exibly. Bagging is then applied to construct various SVM models to reduce the variance in the prediction by the median of forecasts from the constructed models. The enhanced prediction ability of the proposed modified SVM-based model with respect to a bagged multiple linear regression (MLR), simple SVM, and simple MLR model is also demonstrated. The results show that the proposed modified SVM-based model outperforms the prediction ability of the other models in all of the adopted evaluation scores.
  • Molecular and biokinetic characterization of methylotrophic denitrification using nitrate and ...Vladimir Baytshtok, Sungpyo Kim, Ran Yu, Hongkeun Park, and Kartik Chandran | Water Science & Technology [+]
    Abstract: Although methanol is a widely employed carbon source for denitrification, relatively little is known on the abundance and diversity of methylotrophic bacteria in activated sludge. The primary aim of this study was to specifically identify bacteria that metabolized methanol in a sequencing batch denitrifying reactor (SBDR), using a novel technique, stable isotope probing (SIP) of 13C labeled DNA. A secondary aim was to quantitatively track dominant methylotrophic bacteria in the SBDR exposed to different terminal electron acceptors. SIP enabled 13C 16S rDNA clone libraries revealed that SBDR methylotrophic populations were related to Methyloversatilis spp. and Hyphomicrobium spp. Based on newly developed quantitative polymerase chain reaction (qPCR) assays, Hyphomicrobium spp. were more abundant than Methyloversatilis spp. throughout the period of SBDR operation. The relative population abundance was stable despite a shift in electron acceptor from nitrate to nitrite (keeping the same methanol dose). However, the shift to nitrite resulted in a significant decrease in denitrification biokinetics on both nitrate and nitrite.
  • Multi-objective Particle Swarm Optimization for Generating Optimal Trade-offs in Reservoir OperationM. Janga Reddy and D. Nagesh Kumar | Hydrological Processes [+]
    Abstract: A multi-objective particle swarm optimization (MOPSO) approach is presented for generating Pareto-optimal solutions for reservoir operation problems. This method is developed by integrating Pareto dominance principles into particle swarm optimization (PSO) algorithm. In addition, a variable size external repository and an efficient elitist-mutation (EM) operator are introduced. The proposed EM-MOPSO approach is first tested for few test problems taken from the literature and evaluated with standard performance measures. It is found that the EM-MOPSO yields ef?cient solutions in terms of giving a wide spread of solutions with good convergence to true Pareto optimal solutions. On achieving good results for test cases, the approach was applied to a case study of multi-objective reservoir operation problem, namely the Bhadra reservoir system in India. The solutions of EM-MOPSOs yield a trade-off curve/surface, identifying a set of alternatives that de?ne optimal solutions to the problem. Finally, to facilitate easy implementation for the reservoir operator, a simple but effective decision-making approach was presented. The results obtained show that the proposed approach is a viable alternative to solve multi-objective water resources and hydrology problems.
  • Multiobjective Differential Evolution with Application to Reservoir System OptimizationM. Janga Reddy and D. Nagesh Kumar | Journal of Computing in Civil Engineering [+]
    Abstract: Many water resources systems are characterized by multiple objectives. For multiobjective optimization, typically there can be no single optimal solution which can simultaneously satisfy all the goals, but rather a set of technologically efficient noninferior or Pareto optimal solutions exists. Generating those Pareto optimal solutions is a challenging task and often difficulties arise in using the conventional methods. In the optimization of reservoir systems, most of the times there is interdependence among one or more decision variables. Recently, it is emphasized that the evolutionary operators used in differential evolution algorithms are very much suitable for problems having interdependence among the decision variables. This paper utilizes this aspect and presents an ef?cient and effective approach for multiobjective optimization, namely multiobjective differential evolution MODE algorithm with an application to a case study in reservoir system optimization. The developed MODE algorithm is first tested on a few benchmark test problems and validated with standard performance measures by comparing them with the nondominated sorting genetic algorithm-II. On achieving satisfactory performance for test problems, it is applied to generate Pareto optimal solutions to a multiobjective reservoir operation problem. It is found that MODE provides many alternative Pareto optimal solutions with uniform coverage and convergence to true Pareto optimal fronts. The results obtained show that the proposed MODE can be a viable alternative for generating optimal trade-offs in multiobjective optimization of water resources systems.
  • Modeling multivariable hydrological series: Principal or independent component analysis?Westra S., C. Brown, U. Lall, A. Sharma | Water Resources Research [+]
    Abstract: The generation of synthetic multivariate rainfall and/or streamflow time series that accurately simulate both the spatial and temporal dependence of the original multivariate series remains a challenging problem in hydrology and frequently requires either the estimation of a large number of model parameters or significant simplifying assumptions on the model structure. As an alternative, we propose a relatively parsimonious two-step approach to generating synthetic multivariate time series at monthly or longer timescales, by first transforming the data to a set of statistically independent univariate time series and then applying a univariate time series model to the transformed data. The transformation is achieved through a technique known as independent component analysis (ICA), which uses an approximation of mutual information to maximize the independence between the transformed series. We compare this with principal component analysis (PCA), which merely removes the covariance (or spatial correlation) of the multivariate time series, without necessarily ensuring complete independence. Both methods are tested using a monthly multivariate data set of reservoir inflows from Colombia. We show that the discrepancy between the synthetically generated data and the original data, measured as the mean integrated squared bias, is reduced by 25% when using ICA compared with PCA for the full joint distribution and by 28% when considering marginal densities in isolation. These results suggest that there may be significant benefits to maximizing statistical independence, rather than merely removing correlation, when developing models for the synthetic generation of multivariate time series.
  • Modelagem Estocástica e Análise Temporal da Duração e Dos Dias de Início e Fim da Estação ChuvosaCarlos Henrique Ribeiro Lima and Upmanu Lall | XVIII Simpósio Brasileiro de Recursos Hídricos [+]
    Abstract: The modeling and ability to predict the onset and end of the rainy season is extremely important in regions of rain-fed agriculture, such as Northeast Brazil. Knowing in advance the most likely period of rainfall, one can minimize losses and better manage the water resources. Here we propose a new methodology to determine the rainy season onset and end. The stochastic model is developed using logistic regression and Fourier series in order to address the probability and seasonality of the daily rainfall for each year of the historical record. The results obtained using 504 rainfall gauges in Northeast show three regions with different seasonal patterns: southwest, north and along the coast. The rainy season identified for those regions is coherent with the literature and covers the periods: Nov-Mar, Feb-May and Mar-Aug. An analysis of the interannual variability of those periods shows a trend of earlier onsets and an increase in the rainy season duration for the three regions, probably resulting from an increase in the sea temperature of the tropical south Atlantic. Finally, the proposed methodology is a basis for the development of an operational forecast model for the onset, peak and end of the rainy season across Northeast.
  • In pursuit of the millenium development goals in water and sanitationCasey Brown and Arthur Holcombe | Water Policy [+]
    Abstract: In recognition of the United Nations designating 2003 as the ‘‘Year for Fresh Water’’ and the endorsement of the Millennium Development Goals (MDG) in water and sanitation, the United Nations Association of Greater Boston (UNA-GB) convened speakers to address strategies for meeting these goals. Water professionals from the public sector, private sector and non-governmental organizations shared their experiences and recommendations. Over the course of the discussions, three themes emerged that appear critical for implementing successful water initiatives. First, the water and sanitation financing gap requires mobilization of local capital through innovative financial tools. Second, public institutions that manage water must be focused and enabled to carry out their mandate effectively. Private sector collaboration can only succeed when coupled with strong public partners. Third, the MDG cannot be met with conventional technological approaches. Technology must be appropriate to the financial and technical context to which it is applied and must engender efficient use of water resources.
  • Indian summer monsoon rainfall and its link with ENSO and Indian Ocean climate indicesChie Ihara, Yochanan Kushnir, Mark A. Cane and Victor H. De La Pena | International Journal of Climatology [+]
    Abstract: We examine the relationship between the state of the equatorial Indian Ocean, ENSO, and the Indian summer monsoon rainfall using data from 1881 to 1998. The zonal wind anomalies and SST anomaly gradient over the equatorial Indian Ocean are used as indices that represent the condition of the Indian Ocean. Although the index defined by the zonal wind anomalies correlates poorly with Indian summer monsoon rainfall, the linear reconstruction of Indian summer monsoon rainfall on the basis of a multiple regression from the NINO3 and this wind index better specifies the Indian summer monsoon rainfall than the regression with only NINO3. Using contingency tables, we ?nd that the negative association between the categories of Indian summer monsoon rainfall and the wind index is significant during warm years (El Nino) but ˜ not during cold years (La Nina). Composite maps of land precipitation also indicat ˜ e that this relationship is significant during El Nino events. We conclude that there is a signi?cant negativ ˜ e association between Indian summer monsoon rainfall and the zonal wind anomalies over the equatorial Indian Ocean during El Nino events. A similar investigation of the relationship ˜ between the SST index and Indian summer monsoon rainfall does not reveal a significant association.
  • Integrated Management of the Blue Nile Basin in Ethiopia: Hydropower and Irrigation ModelingPaul J. Block, Kenneth Strzepek, and Balaji Rajagopalan, | International Food Policy Research Institute [+]
    Abstract: Ethiopia is at a critical crossroads with a large and increasing population, a depressed national economy, insufficient agricultural production, and a low number of developed energy sources. The upper Blue Nile basin harbors considerable untapped potential for irrigation and hydropower development and expansion. Numerous hydrologic models have been developed to assess hydropower and agricultural irrigation potential within the basin, yet often fail to adequately address critical aspects, including the transient stages of large-scale reservoirs, relevant flow retention policies and associated downstream ramifications, and the implications of stochastic modeling of variable climate and climate change. A hydrologic model with dynamic climate capabilities is constructed to assess these aspects. The model indicates that largescale development typically produces benefit-cost ratios from 1.2-1.8 under historical climate regimes for the projects specified. Climate change scenarios indicate potential for small benefit-cost increases, but reflect possible significant decreases. Stochastic modeling of scenarios representing a doubling of the historical frequency of El Niño events indicates benefit-cost ratios as low as 1.0 due to a lack of timely water. An evaluation of expected energy growth rates reinforces the need for significant economic planning and the necessity of securing energy trade contracts prior to extensive development. A Ramsey growth model for energy development specifies project multipliers on total GDP over the 100-year simulation ranging from 1.7-5.2, for various climatologic conditions.
  • Interannual Variability and Ensemble Forecast of Upper Blue Nile Basin Kiremt Season PrecipitationPaul J. Block and Balaji Rajagopalan | Journal of Hydrometeorology [+]
    Abstract: Ethiopian agriculture and Nile River flows are heavily dependent upon the Kiremt season (June– September) precipitation in the upper Blue Nile basin, as a means of rain-fed irrigation and streamflow contribution, respectively. Climate diagnostics suggest that the El Niño–Southern Oscillation phenomenon is a main driver of interannual variability of seasonal precipitation in the basin. One-season (March–May) lead predictors of the seasonal precipitation are identified from the large-scale ocean–atmosphere–land system, including sea level pressures, sea surface temperatures, geopotential height, air temperature, and the Palmer Drought Severity Index. A nonparametric approach based on local polynomial regression is proposed for generating ensemble forecasts. The method is data driven, easy to implement, and provides a flexible framework able to capture any arbitrary features (linear or nonlinear) present in the data, as compared to traditional linear regression. The best subset of predictors, as determined by the generalized cross-validation (GCV) criteria, is selected from the suite of potential large-scale predictors. A simple technique for disaggregating the seasonal precipitation forecasts into monthly forecasts is also provided. Cross-validated forecasts indicate significant skill in comparison to climatological forecasts, as currently utilized by the Ethiopian National Meteorological Services Agency. This ensemble forecasting framework can serve as a useful tool for water resources planning and management within the basin.
  • Multipurpose Reservoir Operation Using Particle Swarm OptimizationD. Nagesh Kumar and M. Janga Reddy | Journal of Water Resources Planning and Management [+]
    Abstract: This paper presents an efficient and reliable swarm intelligence-based approach, namely elitist-mutated particle swarm optimization EMPSO technique, to derive reservoir operation policies for multipurpose reservoir systems. Particle swarm optimizers are inherently distributed algorithms, in which the solution for a problem emerges from the interactions between many simple individuals called particles. In this study the standard particle swarm optimization PSO algorithm is further improved by incorporating a new strategic mechanism called elitist-mutation to improve its performance. The proposed approach is ?rst tested on a hypothetical multireservoir system, used by earlier researchers. EMPSO showed promising results, when compared with other techniques. To show practical utility, EMPSO is then applied to a realistic case study, the Bhadra reservoir system in India, which serves multiple purposes, namely irrigation and hydropower generation. To handle multiple objectives of the problem, a weighted approach is adopted. The results obtained demonstrate that EMPSO is consistently performing better than the standard PSO and genetic algorithm techniques. It is seen that EMPSO is yielding better quality solutions with less number of function evaluations.
  • Municipal Water Plan for Milhã, Ceará in Brazil: Seeking universalization and water sustainability (English version)Francisco de Assis de Souza Filho, Silvrano Adonias Neto, Francisco Osny Enéas da Silva, Daniele Costa da Silva, Cristine Ferreira Gomes Viana, Eliane Ferreira da Silva Mota, Felipe Nogueira Cadengue de Lucena, José Hebert Medeiros Almeida, Bruno Marinho [+]
    This Municipal Water Plan for the municipality of Milhã in the state of Ceará, Brazil was written by a team at the Federal University of Ceará in coordination with the Columbia Water Center. The plan is a tool to be used for building drinking water infrastructure in the rural communities of the municipality. The plan should be used as a template for planning in other municipalities. Also available in Portuguese at: http://water.columbia.edu/files/2012/06/PAM_PT_COMPLETO.pdf
  • Physiological State, Growth Mode, and Oxidative Stress Play a Role in Cd(II)-Mediated Inhibition ...Kartik Chandran and Nancy G. Love | Applied and Environmental Microbiology [+]
    Abstract: The goal of this study was to determine the impact of physiological growth states (batch exponential and batch stationary growth) and growth modes (substrate-limited chemostat, substrate-sufficient exponential batch, and substrate-depleted stationary batch growth) on several measures of growth and responses to Cd(II)-mediated inhibition of Nitrosomonas europaea strain 19718. The specific oxygen uptake rate (sOUR) was the most sensitive indicator of inhibition among the different responses analyzed, including total cell abundance, membrane integrity, intracellular 16S rRNA/DNA ratio, and amoA expression. This observation remained true irrespective of the physiological state, the growth mode, or the mode of Cd(II) exposure. Based on the sOUR, a strong time-dependent exacerbation of inhibition (in terms of an inhibition coef?cient [Ki ]) in exponential batch cultures was observed. Long-term inhibition levels (based on Ki estimates) in metabolically active chemostat and exponential batch cultures were also especially severe and comparable. In contrast, the inhibition level in stationary-phase cultures was 10-fold lower and invariable with exposure time. Different strategies for surviving substrate limitation (a 10-fold increase in amoA expression) and starvation (the retention of 16S rRNA levels) in N. europaea cultures were observed. amoA expression was most negatively impacted by Cd(II) exposure in the chemostat cultures, was less impacted in exponential batch cultures, and was least impacted in stationary batch cultures. Although the amoA response was consistent with that of the sOUR, the amoA response was not as strong. The intracellular 16S rRNA/DNA ratio, as determined by fluorescence in situ hybridization, also did not uniformly correlate with the sOUR under conditions of inhibition or no inhibition. Finally, Cd(II)-mediated inhibition of N. europaea was attributed partially to oxidative stress.
  • Predictability of Western Himalayan river flow: melt seasonal inflow into Bhakra Reservoir in northern IndiaIndrani Pal, Upmanu Lall, Andrew Robertson, Mark A Cane, and Rajeev Bansal | Submitted to Journal of Hydrology [+]
    Abstract: Snowmelt dominated streamflow of the Western Himalayan rivers is an important water resource during the dry pre-monsoon months to meet the irrigation and hydropower needs in northern India. This study is one of the first to look at the seasonal prediction of melt- dominated total inflow into the Bhakra Dam in northern India, based on statistical relationships with meteorological variables during the preceding winter. Total inflow into the Bhakra dam includes the Satluj River flow together with a flow diversion from its tributary, the Beas River, both of which originate from the Western Himalayas. Both are tributaries of the Indus River. Average measured winter snow volume at the upper elevation stations and corresponding lower elevation rainfall and temperature of Satluj River basin were considered as empirical predictors. A variety of information criteria as well as cross-validation were used to select the best subset of inputs for a Generalized Linear Model (GLM). Forecasts of the melt season at the end of winter and as the melt season commences are shown to have potential skill for guiding the development of stochastic optimization models to manage the trade-off between irrigation and hydropower releases versus flood control during the annual fill cycle of the Bhakra reservoir that is a major energy and irrigation source in the region. Keywords – Predictability; Spring Inflow; Bhakra dam; Satluj River; Western Himalaya; India.
  • Predictive downscaling based on non-homogeneous hidden Markov modelsAbedalrazq F. Khalil, Hyun-Han Kwon, Upmanu Lall & Yasir H. Kaheil | Hydrological Sciences Journal [+]
    Abstract: Weather-state models have been shown to be effective in downscaling the synoptic atmospheric information to local daily precipitation patterns. We explore the ability of non-homogeneous hidden Markov models (NHMM) to downscale regional seasonal climate data to daily rainfall at a collection of gauging sites. The predictors used are: ensemble means of seasonal rainfall as forecast by the DEMETER and ECHAM models, and the preceding seasonal outgoing long-wave radiation (OLR). As the downscaling of seasonal GCM-based predictions lacks the ability to capture the intra-seasonal variability, we augment the seasonal GCM-driven inputs with statisticallydriven predictions of the monthly rainfall amounts. The pooling effect of combining seasonal and monthly estimates of the regional rainfall enhances the capacity of the NHMM to simulate the stochastic characteristics of rainfall fields. The monthly rainfall prediction is derived from a wide range of climate precursors such as the El NiñoSouthern Oscillation, local sea-level pressure, and sea-surface temperature. Application of the methodology to data from the Everglades National Park region in South Florida, USA is presented for the seasons May–July and August– September using a 22-year sequence of seasonal data from eight rainfall stations. The model skill in capturing the seasonal and intra-seasonal rainfall attributes at each station is demonstrated graphically and using simple statistical measures of efficiency. The hidden states derived from NHMM are qualitatively analysed and shown to correspond to the dominant synoptic-scale features of rainfall generating mechanisms, which reinforces the argument that physical processes are appropriately captured.
  • Probabilistic prediction of hydroclimatic variables with nonparametric quantification of uncertaintyRajib Maity and D. Nagesh Kumar | Journal of Geophysical Research [+]
    Abstract: A semiparametric, copula-based approach is proposed to capture the dependence between teleconnected hydroclimatic variables for the prediction of response variable using the information of climate precursors. The copulas have an excellent property to study the scale-free dependence structure while preserving such dependence during simulation. This property is utilized in the proposed approach. The usefulness of the proposed method can be recognized in three distinct aspects: (1) It captures the dependence pattern preserving scale-free or rank-based ‘‘measure of association’’ between the variables. (2) The proposed method is able to quantify the uncertainty associated with the relationship between teleconnected variables due to various factors; thus, the probabilistic predictions are available along with information of uncertainty. (3) Instead of parametric probability distribution, nonparametrically estimated probability densities for data sets can be handled by the proposed approach. Thus, the proposed method can be applied to capture the relationship between teleconnected hydroclimatic variables having some linear and/or nonlinear cause-effect relationship. The proposed method is illustrated by an example of the most discussed problem of Indian summer monsoon rainfall (ISMR) and two different large-scale climate precursors, namely, El Nin˜ o – Southern Oscillation (ENSO) and Equatorial Indian Ocean Oscillation (EQUINOO). The dependence between them is captured and investigated for its potential use to predict the monthly variation of ISMR using the proposed method. Predicted rainfall is shown to correspond well with the observed rainfall with a correlation coefficient of 0.81 for the summer monsoon months, i.e., June through September. Moreover, the uncertainty associated with the predicted values is also made available through boxplots. The method, being general, can be applied to similar analysis to assess the dependence between teleconnected hydroclimatic variables for other regions of the world and for different temporal scales such as seasonal.
  • Optimal Reservoir Operation for Irrigation of Multiple Crops using Elitist-mutated Particle Swarm...M. JANGA REDDY & D. NAGESH KUMAR | Hydrological Sciences [+]
    Abstract: To achieve social and economic sustainability in arid and semi-arid areas under water scarce situations, it is vital to promote efficient use of water through improved management of water resources. This paper presents a swarm optimization based solution to a detailed operational model for short-term reservoir operation for irrigation of multiple crops. The model integrates the dynamics associated with the water released from a reservoir to the actual water utilized by crops at farm level. It takes into account the nonlinear relationship of root growth, soil heterogeneity, soil moisture dynamics for multiple crops, yield response to water deficit at various growth stages of the crops and economic benefits from the crops. As the developed model is a nonlinear one, it is solved using a novel global optimization technique, namely elitist-mutation particle swarm optimization (EMPSO). The model’s applicability is demonstrated through a case study of Malaprabha Reservoir system in Southern India. The performance of the model is examined for different water deficit conditions and the sensitivity of the crop yield is analysed for water shortage at various growth stages. Also, the consideration of economic benefits in the objective function and its effect on the water allocation decisions for multiple crops are studied. Consequently, the output from the model includes initial storages, releases, overflows and evaporation losses for each 10-day period on the reservoir side; and allocation of water, actual evapotranspiration and initial soil moisture for each crop for each 10-day period on the field side, thus facilitating decision making for optimal utilization of the available water resources.
  • Off-grid energy services for the poor: Introducing LED lighting in the Millennium Villages Projectin MalawiEdwin Adkins, Sandy Eapen, Flora Kaluwile, Gautam Nair, Vijay Modi | Energy Politics [+]
    Abstract: Lanterns that use light-emitting diodes (LEDs) powered by batteries, which are in turn charged by grid electricity or small solar panels, have emerged as a cost-competitive alternative to kerosene and other fuel-based lighting technologies, offering brighter light for longer duration at equal or lower cost over time. This paper presents lessons learned from the introduction of solar LED lanterns in rural Malawi. We discuss a market-based program using new and existing local commercial structures such as vendors and cooperatives to sell lanterns to village households without subsidy. The paper addresses issues of enterprise development, community interactions, and survey data on lighting use and expenditure patterns before and after LED lantern introduction. Households that purchased a lantern reported high levels of satisfaction with the LED lanterns as well as savings in annual kerosene expenditure comparable to the price of the lantern. These households also reported monthly incomes comparable to the price of the LED lanterns whereas non-adopters surveyed reported monthly incomes about half this level, suggesting a need for ?nancing options to maximize adoption among poorer populations in rural areas. These results suggest that similar market based models of LED lighting technology dissemination have the potential to be replicated and scaled up in other off-grid regions in developing countries. However, viability of local cooperatives and supply chains for lantern products over the medium-to-long term remain to be assessed.
  • Municipal Water Plan for Milhã, Ceará in Brazil: Seeking universalization and water sustainability (Portuguese version)Francisco de Assis de Souza Filho, Silvrano Adonias Neto, Francisco Osny Enéas da Silva, Daniele Costa da Silva, Cristine Ferreira Gomes Viana, Eliane Ferreira da Silva Mota, Felipe Nogueira Cadengue de Lucena, José Hebert Medeiros Almeida, Bruno Marinho [+]
    This Municipal Water Plan for the municipality of Milhã in the state of Ceará, Brazil was written by a team at the Federal University of Ceará in coordination with the Columbia Water Center. The plan is a tool to be used for building drinking water infrastructure in the rural communities of the municipality. The plan should be used as a template for planning in other municipalities. Also available in English at: http://water.columbia.edu/files/2012/06/PAM_ENG_COMPLETE.pdf
  • N2O Emissions from Activated Sludge Processes 2008-2009: Results of a National Monitoring Survey ...Joon Ho Ahn, Sungpyo Kim, Hongkeun Park, Brian Rahm, Krishna Pagilla, and Kartik Chandran | Environmental Science and Technology [+]
    Abstract: Despite recognition of the possible role of biological nitrogen removal (BNR) processes in nitrous oxide (N2O) emission, a measured database of N2O emissions from these processes at the national scale does not currently exist. This study focused on the quantification of N2O emissions at 12 wastewater treatment plants (WWTPs) across the United States using a newly developed U.S. Environmental Protection Agency (USEPA) reviewed protocol. A high degree of variability in field-scale measurements of N2O was observed, both across the WWTPs sampled and within each WWTP. Additionally, aerobic zones, which have hitherto not been considered in the USEPA approach of estimating N2O emissions, generally contributed more to N2O ?uxes than anoxic zones from BNR reactors. These results severely qualify the conventional use of a single emission factor to “estimate” N2O emissions from BNR processes, solely by virtue of denitrification. Upon subjecting the nationwide data set to multivariate regression data mining, high nitrite, ammonium, and dissolved oxygen concentrations were positively correlated with N2O emissions from aerobic zones of activated sludge reactors. On the other hand, high nitrite and dissolved oxygen concentrations were positively correlated with N2O emissions from anoxic zones. Based on these results, it can be argued that activated sludge processes that minimize transient or permanent build up of ammonium or nitrite, especially in the presence of dissolved oxygen, are expected to have low N2O emissions.
  • North American droughts of the mid to late nineteenth century: a history, simulation and ...Herweijer, C., R. Seager, and E. R. Cook | The Holocene [+]
    Abstract: Unlike the major droughts of the twentieth century that are readily identified in the instrumental record, similar events in the nineteenth century have to be identified using a combination of proxy data, historical accounts and a sparse collection of early instrumental records. In the USA, three distinct periods of widespread and persistent drought stand out in these records for the latter half of the nineteenth century: 1856/1865, 1870/1877 and 1890/1896. Each of these events is shown to coincide with the existence of an anomalously cool, La Nin˜a-like tropical Pacific. To examine the physical mechanisms behind these droughts two ensembles of simulations with an atmosphere general circulation model (AGCM) were generated: the first forces an AGCM with the observed history of Sea Surface Temperatures (SSTs) everywhere from 1856 to 2001 (the GOGA experiment), the second forces the AGCM only with tropical Pacific SSTs, being coupled to a two-layer entraining mixed layer (ML) ocean elsewhere (the POGA-ML experiment). Owing to a sparsity of instrumental precipitation data at this time, proxy evidence from tree rings is used as verification. A comparison of modelled soil moisture with tree-ring reconstructions of the Palmer Drought Severity Index (PDSI), a proxy for soil moisture, from the North American Drought Atlas is made. Both the POGA-ML and GOGA ensemble means capture the three multi-year droughts of the mid to late nineteenth century, indicating that the droughts were SST forced. The similarity of the POGAML and GOGA simulations implies that the component of each drought signal that is forced by the SST is driven ultimately by the La Nin˜a-like tropical Pacific. The global atmosphere/ocean context of each of the mid to late-nineteenth century droughts reveals a zonally and hemispherically symmetric pattern consistent with forcing from the tropics. In addition, Rossby wave propagation from the cooler equatorial Pacific amplifies dry conditions over the USA. Finally, using published coral data for the last millennium to reconstruct a NINO 3.4 history, the modern-day relationship between NINO 3.4 and North American drought is applied to recreate two of the severest Mediaeval ‘drought epochs’ in the western USA. The large-scale spatial similarity to the Drought Atlas data demonstrates the potential link between a colder eastern equatorial Pacific and the persistent North American droughts of the Mediaeval period.
  • Improving the Prediction of Winter Precipitation and Temperature over the continental US: Role ...Naresh Devineni and A. Sankarasubramanian | Monthly Weather Review [+]
    Abstract: Recent research in seasonal climate prediction has focused on combining multiple atmospheric General Circulation Models (GCMs) to develop multimodel ensembles. A new approach to combine multiple GCMs is proposed by analyzing the skill of candidate models contingent on the relevant predictor(s) state. To demonstrate this approach, we combine historical simulations of winter (December-February, DJF) precipitation and temperature from seven GCMs by evaluating their skill – represented by Mean Square Error (MSE) – over similar predictor (DJF Nino3.4) conditions. The MSE estimates are converted into weights for each GCM for developing multimodel tercile probabilities. A total of six multimodel schemes are considered that includes combinations based on pooling of ensembles as well as based on the long-term skill of the models. To ensure the improved skill exhibited by the multimodel scheme is statistically significant, we perform rigorous hypothesis tests comparing the skill of multimodels with individual models’ skill. The multimodel combination contingent on Nino3.4 show improved skill particularly for regions whose winter precipitation and temperature exhibit significant correlation with Nino3.4. Analyses of weights also show that the proposed multimodel combination methodology assigns higher weights for GCMs and lesser weights for climatology during El Nino and La Nina conditions. On the other hand, due to the limited skill of GCMs during neutral conditions over the tropical Pacific, the methodology assigns higher weights for climatology resulting in improved skill from the multimodel combinations. Thus, analyzing GCMs’ skill contingent on the relevant predictor state provide an alternate approach for multimodel combination such that years with limited skill could be replaced with climatology.
  • Improving Livelihoods by Improving Water Access for Small-Scale Agriculture: Two Case Studies of Improved Farming Inputs and Financing in Toya and Tiby, MaliLakis Polycarpou, Mika Manga, Samantha Tress, Vijay Modi [+]
    The premise of this project was to explore the idea of creating access to water in the “off-season” to women for growing fruits and vegetables. Creating vegetable gardening at the small-scale while targeting women serves to economically empower women, something vital in a society where otherwise rice farming income goes almost exclusively to men.
  • El Niño-Southern Oscillation Influences on Rice Production in Sri LankaLareef Zubair | International Journal of Climatology [+]
    Abstract: Despite advances in the capacity to predict the evolution of the El Nino–southern oscillation (ENSO) phenomenon and ˜ advances in understanding the in?uence of ENSO on rainfall in tropical regions such as Sri Lanka, there has been limited use of climate predictions for agricultural decision-making. Climatic fluctuations have a profound influence on the cultivation of crops such as rice, which is the staple food in Sri Lanka. Here, the relationship between the sea-surface temperature-based ENSO index of NINO3.4, rainfall and the departure of Sri Lankan rice production from long-term trends, is analysed for the ‘Maha’ (October to March) and ‘Yala’ (April to September) cultivation seasons between 1952 and 1997. During the El Nino phase, the ˜ Maha rice production frequently increased (10 out of 15 seasons) and the Yala production frequently decreased (10 out of 14 seasons). Conversely, during the La Nina phase, the ˜ Maha production decreased (seven out of ten seasons) and Yala production increased (six out of eight seasons). Floods, state interventions, civil disturbances, fertilizer price hikes and extreme anomalies in the previous season were noted in the majority of seasons in which these ENSO–production linkages were violated. The correlation of the Maha rice production anomaly with the average NINO3.4 from October to December was significant at the 5% level and that with the aggregate October to December rainfall was significant at the 1% level. Yala rice production showed a significant relationship with concurrent NINO3.4 and a strong correlation (r = 0.60) with the previous season’s rainfall. Yala cultivation is water constrained, and carryover storage from the previous season is often used to determine the extent of planting. The relationships between ENSO and seasonal rice production and the relationship between Yala rice production and previous Maha rainfall could be used for agricultural management and policy formulation.
  • El Niño-Southern Oscillation-based index insurance for floods: Statistical risk analyses and ...Khalil A. F., H.-H. Kwon, U. Lall, M. J. Miranda, J. Skees | Water Resources Research [+]
    Abstract: Index insurance has recently been advocated as a useful risk transfer tool for disaster management situations where rapid fiscal relief is desirable and where estimating insured losses may be difficult, time consuming, or subject to manipulation and falsification. For climate-related hazards, a rainfall or temperature index may be proposed. However, rainfall may be highly spatially variable relative to the gauge network, and in many locations, data are inadequate to develop an index because of short time series and the spatial dispersion of stations. In such cases, it may be helpful to consider a climate proxy index as a regional rainfall index. This is particularly useful if a long record is available for the climate index through an independent source and it is well correlated with the regional rainfall hazard. Here El Nin˜ o–Southern Oscillation (ENSO) related climate indices are explored for use as a proxy to extreme rainfall in one of the districts of Peru, Piura. The ENSO index insurance product may be purchased by banks or microfinance institutions to aid agricultural damage relief in Peru. Crop losses in the region are highly correlated with floods but are difficult to assess directly. Beyond agriculture, many other sectors suffer as well. Basic infrastructure is destroyed during the most severe events. This disrupts trade for many microenterprises. The reliability and quality of the local rainfall data are variable. Averaging the financial risk across the region is desirable. Some issues with the implementation of the proxy ENSO index are identified and discussed. Specifically, we explore (1) the reliability of the index at different levels of probability of exceedance of maximum seasonal rainfall, (2) the effect of sampling uncertainties and the strength of the proxy’s association to local outcome, (3) the potential for clustering of payoffs, (4) the potential that the index could be predicted with some lead time prior to the flood season, and (5) evidence for climate change or nonstationarity in the flood exceedance probability from the long ENSO record.
  • El Niños tropical climate and teleconnections as a blueprint for pre-Ice-Age climatesPeter Molnar and Mark A. Cane | Paleoceanography [+]
    Abstract: At about 2.7 million years ago (Ma) the warm equable climates of early and middle Pliocene time (5-2.7 Ma) were replaced by recurring ice ages. Most attempts to explain the change appeal either to changes in CO2 in the atmosphere or to reduced heat transport by the Atlantic Ocean. The sources of the strongest teleconnections in the current climate, however, lie in the tropics, and such connections occur by transport of heat and moisture by the atmosphere. The most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial Pacific, ENSO variations, with warm and dry or cool and wet variations in in extratropical climates. We show that early and middle Pliocene climates, both in equatorial regions and in the extratropics, differ from present-day climates, in most cases, with the same spatial pattern as that associated with ENSO. A virtually permanent El Nino-like state appears to have characterized pre-Ice-Age climates, suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth.
  • Energy, water and phenology controls on the annual carbon and water cyclesJ Green, P Gentine, J Berry, J Lee, J Kolassa | 2014 AGU Presentation
  • Economic Analysis of Large-Scale Upstream River Basin Development on the Blue Nile in Ethiopia ...Paul Block and Kenneth Strzepek | Journal of Water Resources Management and Planning [+]
    Abstract: The upper Blue Nile Basin in Ethiopia harbors considerable untapped potential for irrigation and large-scale hydropower development and expansion. Numerous water resources system models have been developed to evaluate these resources, yet often fail to adequately address critical aspects, including the transient e.g., filling stages of reservoirs, relevant streamflow retention policies and downstream consequences, construction staggering, and the implications of stochastic modeling of variable climate and climate change. This omission has clear economic impacts on benefits and costs and could be pivotal in national policy and decision making. The Investment Model for Planning Ethiopian Nile Development dynamic water resources system model is outlined and applied to address these aspects. For the hydropower and irrigation development projects specified, model results disregarding transient and construction stagger aspects demonstrate overestimations of $6 billion in benefits and 170% in downstream flows compared to model results accounting for these aspects. Benefit-cost ratios for models accounting for transient conditions and climate variability are found to range from 1.2–1.8 under historical climate regimes for the streamflow retention policies evaluated. Climate change scenarios, represented either by changes in the frequency of El Niño and La Niña events or by the Special Report on Emissions Scenarios projections, indicate potential for small benefit-cost increases, but also reflect the potential for noteworthy decreases, relative to the historical climate conditions. In particular, stochastic modeling of scenarios representing a doubling of the historical frequency of El Niño events indicates benefit-cost ratios as low as 1.0, even under perfect foresight optimization modeling, due to a lack of timely water. However, even at this ratio, Ethiopia, at current growth rates, may still be unable to absorb all the potential energy developed, reinforcing the need for significant economic planning and the necessity of securing energy trade contracts prior to extensive expansion.
  • Downscaling precipitation to river basin in India for IPCC SRES scenarios using support vector ...Aavudai Anandhi, V. V. Srinivas, Ravi S. Nanjundiah, and D. Nagesh Kumar | International Journal of Climatology [+]
    Abstract: This paper presents a methodology to downscale monthly precipitation to river basin scale in Indian context for special report of emission scenarios (SRES) using Support Vector Machine (SVM). In the methodology presented, probable predictor variables are extracted from (1) the National Center for Environmental Prediction (NCEP) reanalysis data set for the period 1971–2000 and (2) the simulations from the third generation Canadian general circulation model (CGCM3) for SRES emission scenarios A1B, A2, B1 and COMMIT for the period 1971–2100. These variables include both the thermodynamic and dynamic parameters and those which have a physically meaningful relationship with the precipitation. The NCEP variables which are realistically simulated by CGCM3 are chosen as potential predictors for seasonal strati?cation. The seasonal strati?cation involves identi?cation of (1) the past wet and dry seasons through classi?cation of the NCEP data on potential predictors into two clusters by the use of K-means clustering algorithm and (2) the future wet and dry seasons through classi?cation of the CGCM3 data on potential predictors into two clusters by the use of nearest neighbour rule. Subsequently, a separate downscaling model is developed for each season to capture the relationship between the predictor variables and the predictand. For downscaling precipitation, the predictand is chosen as monthly Thiessen weighted precipitation for the river basin, whereas potential predictors are chosen as the NCEP variables which are correlated to the precipitation and are also realistically simulated by CGCM3. Implementation of the methodology presented is demonstrated by application to Malaprabha reservoir catchment in India which is considered to be a climatically sensitive region. The CGCM3 simulations are run through the calibrated and validated SVM downscaling model to obtain future projections of predictand for each of the four emission scenarios considered. The results show that the precipitation is projected to increase in future for almost all the scenarios considered. The projected increase in precipitation is high for A2 scenario, whereas it is least for COMMIT scenario.
  • Detecting shifts in correlation and variability with application to ENSO-Monsoon Rainfall ...L. F. Robinson, V. H. de la Peña, and Y. Kushnir | Theoretical and Applied Climatology [+]
    Abstract: This paper addresses the retrospective detection of step changes at unknown time points in the correlation structure of two or more climate times series. Both the variance of in- dividual series and the covariance between series are ad- dressed. For a sequence of vector-valued observations with an approximate multivariate normal distribution, the proposed method is a parametric likelihood ratio test of the hypothesis of constant covariance against the hypothesis of at least one shift in covariance. The formulation of the test statistic and its asymptotic distribution are taken from Chen and Gupta (2000). This test is applied to the series comprised of the mean summer NINO3 index and the Indian monsoon rainfall index for the years 1871–2003. The most likely change point year was found to be 1980, with a resulting p-value of 0.12. The same test was applied to the series of NINO3 and Northeast Brazil rainfall observations from the years 1856– 2001. A shift was detected in 1982 which is significant at the 1% level. Some or all of this shift in the covariance matrix can be attributed to a change in the variance of the Northeast Brazil rainfall. A variation of this methodology designed to increase power under certain multiple change point alternatives, specificallly when a shift is followed by a reversal, is also presented. Simulations to assess the power of the test under various alternatives are also included, in addition to a review of the literature on alternative methods.
  • Diagnostics of Western Himalayan Satluj River flow: Warm season (MAM/JJAS) inflow into Bhakra dam in IndiaIndrani Pal, Upmanu Lall, Andrew W. Robertson, Mark A. Cane, Rajeev Bansal [+]
    Here we analyze the variability of MAM (March–April–May) and JJAS (June–July–August–September) seasonal Satluj River flow into the Bhakra dam in India through Pearson anomaly correlation and composite analyses with antecedent and concurrent seasonal climatic and atmospheric circulation patterns. The MAM seasonal inflow of Bhakra dam is significantly correlated with winter (DJF/FM) precipitation and temperature of the Satluj basin while the correlation with FM was more prominent for precipitation (snow = +0.72, rainfall = +0.60), and temperature (diurnal temperature range (DTR) = 0.76 and maximum temperature (Tmax) = 0.57). The JJAS inflow was also positively correlated with DJF/FM as well as JJAS precipitation of the Satluj basin while the correlation with basin average FM was the largest (+0.54). These suggested that both MAM and JJAS inflow anomalies are linked with DJF/FM climate over the Western Himalayas and adjoining north and central Indian plains, which were also found to be linked with the fluctuation of equatorial concurrent Sea Surface Temperature anomalies over the western Indian Ocean (max anomaly correlation was > +0.70) and mean sea level pressure over western pole of the Southern Oscillation sea-saw region (max Pearson anomaly correlation was  +0.60). Low (high) MAM inflow was found to be associated with negative (positive) precipitation anomalies over the basin and north India in DJF and FM while FM precipitation anomaly is more concentrated over the Western Himalayas. In addition, low (high) JJAS inflow is also associated with negative (positive) precipitation anomalies over the basin and north India in DJF and over the Western Himalaya in FM and JJAS. Negative geopotential height anomaly at 500 h Pa (Z500) over Siberia and northwestern pacific in DJF, and positive Z500 anomaly over the northwest India in FM were noticed in low MAM inflow years. Whereas high inflow in MAM was linked with a negative Z500 anomaly between two positive Z500 anomaly regions – one over eastern Siberia stretched up to northern Pacific and second over the Eastern Europe in DJF, which gets stronger in FM. We also found southwesterly (northeasterly) wind vectors at 850 h Pa pressure level (uv850) bringing more (less) moisture to the Western Himalayas in DJF and FM in high (low) MAM/JJAS flow years.
  • Diurnal and seasonal variation in surface wind at Sita Eliya, Sri LankaLareef Zubair | Theoretical and Applied Climatology 2002 [+]
    Abstract: Hourly measurements of surface winds at Sita Eliya (6 deg 58 min N, 80 deg 46 min E, 1860 m a.s.l.) located atop the North-South mountain ridge in Sri Lanka were analyzed to investigate the diurnal and seasonal variation in the wind climate. Surface winds are dominated by the monsoon regimes, with Northeasterlies from November to January, Southwesterlies from February to May and Westerlies and Northwesterlies from June to October. through most of the year, the average wind speed is around 6-8 m/s. However from June to August, it is around 10-14 m/s. Wind in June is gusty due to the location of the low-level Easterly jet over Sri Lanka. The wind undergoes a reversal in both zonal and meridional directions in March and November coincident with the migration of the Inter-Tropical Convergence Zone. Notwithstanding the period from May to September being designated as the Southwest monsoon, the wind is from West, South-West-West and North-North-West. During the Southwest monsoon, wind speed during the night is nearly as high as that during the day. This anomalous diurnal variation in wind speeds may be related to orographic influences. The high wind speeds at Sita Eliya in conjunction with the moderate diurnal and seasonal variability in wind speed, is suitable for wind-energy generation.
  • Does Climate Matter? Evaluating the Effects of Climate Change on Future Ethiopian HydropowerPaul Block and Casey Brown | The Third Interagency Conference on Research in the Watersheds [+]
    Abstract: This research aims at quantifying the effect and importance of considering future climate change on large-scale infrastructure in a developing country context. Plans are underway for major hydropower development in Ethiopia, a water resources-rich nation, yet consideration of climate change on design, operation, and eventual benefits of the system remains uncharted. If current strategies are reliant on stationary climate, what future climatic conditions could warrant measurable design changes or even project abandonment? How much do long-term benefits change, and is this level significant, especially considering economic variability, policy, and other competing demands? A vacuum currently exists for decision makers; there is clear recognition that climate change information ought to be considered but little experience in incorporating the seemingly complex science into design and operational decisions. This research aims to establish and demonstrate an approach for integrating climate change information into project evaluation, ultimately creating a serviceable format from which scientists outside of the climate specialty may address climate risk management decisions. To model the system, potential future precipitation and temperature trends are utilized to drive a coupled hydrology–Ethiopian hydropower optimization model, producing project benefit-cost ratios over 50 years. These results are subsequently evaluated through benefit-cost ratio surface illustrations for varying economic, policy, and project scope conditions. Preliminary results suggest nonstationary climate influences may warrant economic attention in comparison with traditionally dominant factors. Additionally, drier than historically normal conditions appear to have a greater detrimental effect on overall benefit-cost ratios than positive effects expected under wetter than normal conditions, a constructive conclusion for early project planning and design.
  • Episodic interannual climate oscillations and their influence on seasonal rainfall in the EvergladesKwon H.-H., U. Lall, Y.-I. Moon, A. F. Khalil, H. Ahn | Water Resources Research [+]
    Abstract: The restoration of the Everglades in Florida is an exemplary ecosystem project. A basic challenge of the restoration project is to operate the hydrologic control structures in a manner that allows the right quantity and quality of water to be delivered at the right times to the right locations. An understanding of long-term variations in seasonal rainfall as well as prospects for the upcoming season are of interest for operational planning. This paper aims to characterize the interannual variability in seasonal rainfall in the Everglades and to identify regions of Pacific and Atlantic oceans whose sea surface temperatures (SSTs) may be the carriers of the lowfrequency information associated with Everglades rainfall. It is now known that interannual and interdecadal quasi-oscillatory phenomena modulate continental rainfall in many places. The amplitudes of these “oscillations” vary with time, and they conform to activity in specific frequency bands. The dominant lowfrequency modes also vary by season. Identifying the climate modes that influence specific low-frequency aspects of rainfall is a challenge that is addressed here using wavelet analysis to diagnose the time-varying low-frequency structure and independent component analysis to identify the spatial modes of variation of the low-frequency signals. The combined approach is termed wavelet-independent component analysis (WICA). In addition to identifying dominant timescales of quasi-oscillatory phenomena that modulate interannual rainfall in the Everglades National Park, we investigate how the amplitude (power) associated with these interannual modes varies at decadal or longer timescales. The analyses presented motivate the need for the development of methods for the analysis and simulation of nonstationary hydroclimatic phenomena. The connection between the resulting low-frequency rainfall modes and sea surface temperatures (SSTs) is then established using correlation analysis using concurrent and preceding season SSTs. The results provide the motivation for the development of a new generation of simulation and forecasting models for rainfall that could directly use such low-frequency information.
  • Epochal Changes in ENSO-Streamflow Relationships in Sri LankaLareef Zubair and Janaki Chandimala | Journal of Hydrometeorology [+]
    Abstract: In an effort to use climate predictions for streamflow and malaria hazard prediction, the decadal variability of the El Niño–Southern Oscillation (ENSO) influence on streamflow and rainfall in the Kelani River in Sri Lanka was investigated based on records from 1925 to 1995. In the last half century, the warm ENSO phase was associated with decreased annual streamflow and the cold ENSO phase with increased streamflow. The annual streamflow had a negative correlation (warm ENSO associated with low streamflow) with the concurrent ENSO index of Niño-3.4 that was significant at the 5% level. This negative correlation with Niño-3.4 is enhanced to a 1% significance level if the aggregate streamflow from January to September alone is considered. There has been a transition in correlation between January–September streamflow and ENSO between the 1950s and 1970s from near or above zero to negative values that have 95% significance levels reminiscent of an epochal shift. This shift was evident when considering the period when the southwest monsoon dominates (April–September) or when correlations were undertaken between the seasonal streamflow and rainfall and the ENSO index in the month prior to each season. Since the relationship between ENSO and Sri Lankan streamflow has strengthened in recent decades the potential for ENSO-based prediction is retained. The epochal shift may also explain why malaria epidemics ceased to co-occur frequently with El Niño episodes after 1945.
  • Hydroclimatic teleconnection between global sea surface temperature and rainfall over India at ...Rajib Maity and D. Nagesh Kumar | Hydrological Processes [+]
    Abstract: It is well established that sea surface temperature (SST) plays a signi?cant role in the hydrologic cycle in which precipitation is the most important part. In this study, the influence of SST on Indian subdivisional monthly rainfall is investigated. Both spatial and temporal influences are investigated. The most influencing regions of sea surface are identified for different subdivisions and for different overlapping seasons in the year. The relative importance of SST, land surface temperature (LST) and ocean– land temperature contrast (OLTC) and their variation from subdivision to subdivision and from season to season are also studied. It is observed that LST does not show much similarity with rainfall series, but, in general, OLTC shows relatively higher influence in the pre-monsoon and early monsoon periods, whereas SST plays a more important role in lateand post-monsoon periods. The in?uence of OLTC is seen to be mostly con?ned to the Indian Ocean region, whereas the effect of SST indicates the climatic teleconnection between Indian regional rainfall and climate indices in Pacific and Atlantic Oceans.
  • Identification of large scale climate patterns affecting snow variability in the eastern U.S.Jennifer Morin, Paul Block, Balaji Rajagopalana, and Martyn Clark | International Journal of Climatology [+]
    Abstract: This study investigates dominant patterns of snow variability and their relationship to large-scale climate circulations over the eastern half of the United States. Two snowfall variables – total seasonal snowfall (TSF) and number of snow days (NSD) – are examined. A principal components (PC) analysis is conducted on data from 124 snowfall stations. The leading mode of variability for both TSF and NSD is driven by the North Atlantic Oscillation (NAO). The secondary mode of variability for TSF is driven by the Pacific/North American pattern (PNA), while the secondary mode of variability for NSD is driven by a dipole pattern and is attributable to regional influences and noise. These patterns exhibit persistence, which provides prospects for seasonal predictions of snowfall variables. This research compliments and extends the work of Serreze et al. (1998), who performed a PC analysis of geopotential heights during the winter season and correlated the spatial patterns of the leading modes of variability with seasonal snowfall values.
  • Impacts of considering climate variability on investment decisions in EthiopiaPaul J. Block, Kenneth Strzepek, Mark W. Rosegrant, Xinshen Diao | Agricultural Economics [+]
    Abstract: Extreme interannual variability of precipitation within Ethiopia is not uncommon, inducing droughts or ?oods and often creating serious repercussions on agricultural and nonagricultural commodities. A dynamic climate module is integrated into an economy-wide model containing a detailed zonal level agricultural structure. This coupled climate-economic model is used to evaluate the effects of climate variability on prospective irrigation and infrastructure investment strategies, and the ensuing country-wide economy. The linkages between the dynamic climate module and the economic model are created by the introduction of a climate-yield factor (CYF), defined at the crop level and varied across Ethiopian zones. Nine sets of variable climate (VC) data are processed by the coupled model, generating stochastic wet and dry shocks, producing an ensemble of potential economic prediction indicators. Analysis of gross domestic product and poverty rate reveal a significant overestimation of the country’s future welfare under all investment strategies when climate variability is ignored. The coupled model ensemble is further utilized for risk assessment to guide Ethiopian policy and planning.
  • Improved Drought Management of Falls Lake Reservoir: Role of Multimodel Streamflow Forecasts in ...Kurt Golembesky, A. Sankarasubramanian, and Naresh Devineni | Journal of Water Resources Planning and Management [+]
    Abstract: Droughts, resulting from natural variability in supply and from increased demand due to urbanization, have severe economic implications on local and regional water supply systems. In the context of short-term monthly to seasonal water management, predicting these supply variations well in advance are essential in advocating appropriate conservation measures before the onset of drought. In this study, we utilized 3-month ahead probabilistic multimodel streamflow forecasts developed using climatic information—sea surface temperature conditions in the tropical Pacific, tropical Atlantic, and over the North Carolina coast—to invoke restrictions for Falls Lake Reservoir in the Neuse River Basin, N.C. Multimodel stream?ow forecasts developed from two single models, a parametric regression approach and semiparametric resampling approach, are forced with a reservoir management model that takes ensembles to estimate the reliability of meeting the water quality and water supply releases and the end of the season target storage. The analyses show that the entire seasonal releases for water supply and water quality uses could be met purely based on the initial storages 100% reliability of supply, thereby limiting the use of forecasts. The study suggests that, by constraining the end of the season target storage conditions being met with high probability, the climate information based streamflow forecasts could be utilized for invoking restrictions during belownormal in?ow years. Further, multimodel forecasts perform better in detecting the below-normal inflow conditions in comparison to single model forecasts by reducing false alarms and missed targets which could improve public con?dence in utilizing climate forecasts for developing proactive water management strategies.
  • Hidroclimatologia De Cheias: Eventos Extremos, Não-estacionariedade, Processos Climáticos De ...Carlos Henrique Ribeiro Lima, Upmanu Lall | II Simpósio de Recursos Hídricos do Sul-Sudeste [+]
    Abstract: In this paper we identify the main flood events into the Brazilian system of hydropower reservoirs. We notice that the greatest floods take place almost simultaneously in most reservoirs of the South and Southeast regions. An increase in the number of events is observed after 1980. A case study of the large scale climate processes associated with the biggest floods of Itaipu is presented. The results show a large influence of the South Atlantic convergence zone on the extreme events, influence that can be extended to most reservoirs in the South and Southeast. Positive anomalies of sea surface temperature in the tropical Pacific, negatives in the air temperature close to the surface in the south Atlantic and positives along the Argentinean cost as well as a westward displacement of the high pressure center in the South Atlantic are associated with the biggest Itaipu floods. A positive trend observed in the flood magnitude along the years identifies itself with an increase in the air temperature close to the surface along the Argentinean coast. Finally, we discuss some methods to incorporate large scale climate information into flood statistical models under scenarios of global climate changes.
  • Fluid DynamicsTobias Siegfried and Lion Summerbell | SEED Magazine [+]
    Abstract: A looming water war in central Asia could mean disaster for the region and beyond.
  • Estimating the performance of international regulatory regimes: Methodology and empirical ...Tobias Siegfried and Thomas Bernauer | Water Resources Research [+]
    Abstract: We develop a methodology for estimating the performance of international regulatory regimes in the context of transboundary surface waters. Our performance metric relies on assessments, over time, of actual performance, counterfactual performance, and optimal performance. The metric is of practical relevance as a diagnostic tool for policy evaluation. Thus it provides a starting point for policy improvement. To demonstrate the empirical relevance of this methodology we examine international water management in the Naryn/Syr Darya basin, a major international river system in Central Asia. The emphasis is on the Toktogul reservoir, the main reservoir in the Naryn/Syr Darya basin, and its downstream effects. The biggest policy challenge in this case has been to design and implement international trade-offs among water releases for upstream hydropower production in winter and water releases for downstream irrigation in summer. We find that the international regime in place since 1998 is characterized by low average performance and high variability.
  • Exploring the effect of hydroclimate variability on economic growth in Sub-Saharan Africa: a ...Casey Brown, Daniela Domeisen, Robyn Meeks, Kenneth Hunu, and Winston Yu | The International Research Institute for Climate and Society [+]
    Abstract: Recent econometric studies provide evidence that climate variability in general, and rainfall variability in particular, has a negative effect on economic growth in the countries of Sub-Saharan Africa. In this study, we explore the factors that may explain why some countries are more resilient to climate variability than others. We use a range of data that is representative of the possible sources of resilience that are commonly hypothesized in the literature, including the state of water resources and water use, the inventory of infrastructure and the quality of institutions. Two analyses are undertaken. In the first, cross country regressions are used to explore aggregate associations of climate and resilience variables with economic growth. In the second, panel regressions for individual countries are performed with drought and flood indices. The results of these regressions are used to specify a water security index. The water security index is then analyzed through the prism of the resilience variables to draw inferences in regard to the sources of resilience that contribute to more water security. The results of these analyses are informative. Cross country regressions confirm the negative association between rainfall variability and economic growth within Sub-Saharan Africa. They also revealed strong associations between Foreign Direct Investment (FDI) and infrastructure inventory and economic growth. An index that accounts for climate variability and water storage (Seasonal Storage Index) is also strongly associated with both FDI and economic growth. The analysis of the Water Security Index revealed that more internal renewable water resources and irrigated agriculture as a percent of agricultural area were associated with more resilience to hydroclimate variability. Water storage was not a strong indicator of resilience, although when controlling for hydrologic variability with the SSI, it does become more important. There were no strong associations with institutions and weak positive associations with road density and phones.
  • Fishing for an Adaptive Governance FrameworkTanya Heikkila | Public Administration Review [+]
    Abstract: Adaptive governance is a concept of growing interest in the environmental policy and management literature (e.g., see Brunner and Steelman et al. 2005; Olsson et al. 2006; Scholz and Stiftel 2005). In general, adaptive governance refers to institutional change processes that are responsive to emerging problems or knowledge surrounding complex ecological systems. While some studies have provided evidence of the benefits of adaptive governance and considered the institutional design features that might support adaptation, few have sought to explain the variance or patterns that emerge as adaptive governance processes unfold. D. G. Webster’s book, Adaptive Governance: The Dynamics of Atlantic Fisheries Management, helps fill this void through its analysis of changes in fisheries management policies under an international regime.
  • Ranking Irrigation Planning Alternatives Using Data Envelopment AnalysisK. Srinivasa Raju and D. Nagesh Kumar | Water Resources Management [+]
    Abstract: Application of Data Envelopment Analysis (DEA) as a Multicriterion Decision Making (MCDM) methodology is tested for Sri Ram Sagar Project, Andhra Pradesh, India to select the suitable irrigation planning alternative. Three different criterion functions of DEA, namely minimizing deviation variable Dj (Min Dj), minimizing maximum deviation (Minmax), and minimizing the sum of deviations Dj (Minsum) are applied for the same DEA constraint set. These criterion functionsare evaluated under the framework of Multi Objective Linear Programming (MOLP). Highest efficiency rated irrigation planning alternative is chosen to be the best for each of the above criterion functions. The results are compared with those obtained by discrete MCDM methods, PROMETHEE and EXPROM. It is found that ranks obtained by DEA are reasonably close to those obtained by the above mentioned MCDM methods, PROMETHEE and EXPROM.