Northeast Urban Climate Risk

Unlike many other parts of the country, residents of the urban Northeastern United States are used to an uninterrupted water supply. New York City’s urban drinking water is one of the purest in the nation. However, given the sheer number of people who depend on this supply, understanding the potential impacts of climate change and variability on the watershed that feeds the reservoirs takes on critical importance.

As part of the National Oceanic and Atmospheric Administration’s (NOAA) Regional Integrated Sciences and Assessments (RISA) Program, The Consortium on Climate Risk in the Urban Northeast (CCRUN) was developed to help stakeholders address the complex challenges and impacts of climate on the Boston-New York-Philadelphia urban corridor. The CCRUN team includes researchers from Columbia University, City College of the City University of New York, Stevens Institute of Technology, the University of Massachusetts, and Drexel University. CCRUN’s initial projects include a focus on Water, Coastal Zones, and Health.

Columbia Water Center scientists are currently working with other CCRUN scientists to understand the long term impacts of climate and potential for drought on the upper Delaware River Basin System, one of the largest water supply systems for the city of New York. The Delaware River Basin Commission and the New York City Department of Environmental Protection are primarily responsible for managing the release of water from the major reservoirs to meet the daily water demand of the city of New York and to maintain the downstream ecosystem.

Today our understanding and management of these reservoir systems (for example, estimation of drought frequency or rules that guide how much water to hold or release in reservoirs) is based on recent historical records. Given that the drought of record in the basin was in the 1960s, it is not clear that these records provide guidance for effective drought preparation and system operation over the long term.

To address the gaps in drought history, researchers at the Lamont-Doherty Tree Ring Lab have begun looking at tree-ring data collected from a number of Delaware River watersheds to provide an accurate estimate of a tree’s age as well as a surrogate for regional climatic conditions of a given period using Hierarchical Bayesian Regression techniques. Based on this reconstructed drought record, researchers believe that while a recurrence of the devastating drought of the 1960s is possible, it is not the most likely risk. On the other hand, there is a much greater chance that the area could experience recurring droughts of shorter duration.

Given that the Delaware system is served by small reservoirs, even a drought of short or moderate duration is of concern. These new insights about the probability, severity and frequency of droughts in the region will provide an important basis for managing New York City’s water supply in the coming years.