1999: Assessing the Impact of Climate and Land-Use/Land-Cover Changes on New York City's Water Supply System

Team Members: Samuel Kirub, Edie Vinson, Reza Khanbilvardi, Reggie Blake, Cynthia Rosenzweig,

The Delaware, Catskill and Croton water supply systems provide drinking water for New York City. These three systems are located about 125 miles to the north and the northwest of the City. The systems are linked in a very innovative and intricate network of storage reservoirs, tunnels and aqueducts that distributes drinking water predominantly via gravity control to the City. The combined systems span a watershed area of approximately 1,900 mi², and they supply on a daily basis an average of slightly less than 1.5 billion gallons of water to nine million people in and around the New York City area.

With expected changes in the primary climate variables of temperature and precipitation and with alterations in land-use/land cover practices, the region's water supply (quantity and quality) may be threatened. Higher temperatures and lower precipitation can decrease the city's water supply by increasing evaporation and reducing runoff from the watersheds that feed the city's reservoirs. The average safe yield of the city's combined water supply system may be drastically decreased. Such a climate scenario could also lead to an increase in the frequency and the severity of droughts and could possibly force New Yorkers to once again filter and drink water from the Hudson river as we had to do during the drought of 1965. For an extreme example, preliminary results show that a drought of the severity that currently occurs about once in one hundred years could occur once in every three to eleven years.

Land-use/land cover changes may exacerbate the problem as they can increase the erosion, the sediment loading and the eutrophication within the watersheds. These, in turn, lead to poor water quality and are detrimental to aquatic life. This study, therefore, assesses the possible impacts on the city's water resources due to climate and land-use/land cover changes. Mitigation and adaptation strategies are suggested.

Climate and land-use/land cover changes are important factors that can alter hydrological processes and consequently influence both water quantity and water quality. A methodology to link remote sensing images, GIS databases, General Circulation Models (GCMs) and hydrological models designed to simulate streamflow, erosion and sediment loads at the watershed scale will be developed as part of a comprehensive study of New York City's water supply system. Two major watersheds within the city's water supply system - Allaben and Neversink (both provide water for the Esopus Creek and ultimately the Ashokan reservoir) - have been selected as case study sites for our research.

This approach to the modeling of watershed scale hydrology for climate change applies state-of-the-art climate change science that will provide information about potential impacts to this vital and complex region's water supply system.

The objectives of the study are the following :

• To ascertain the impact climate and land-use/land cover changes may have had on runoff over the past twenty-five years.
• To assess alterations in the city's future water supply due to possible climate change.
• To assess the implications of climate change on erosion and sediment load.
• To investigate the impact possible climate change may have on the trout population.

Hypothesis

Climate and land-use/land cover changes have, and will continue to, adversely affect New York City's water supply system.

Tasks

• Acquire and quality control the twenty-five years of pertinent hydro-meteorological, vegetation, soil and land-use/land cover data.
• Conduct the runoff simulations based on climate change scenarios.
• Conduct the erosion modeling.

Data Sources and Models:

Hydro-meteorological and climate data will be acquired from GISS, the U.S.G.S, the North East Regional Climate Center and the New York City Department of Environmental Protection.

A suite of models - Hydrological models ( WATBAL, PDSI, WEPP and NASA/GISS land surface model) and General Circulation Models, GCMs, (NASA/Goddard Institute for Space Studies (GISS), Canadian Centre for Climate Modeling and Analysis (CC), and the United Kingdom Hadley Centre (HC) - all run with and without sulphate forcings) along with GIS data bases have been intricately assembled and linked to carry out the objectives of the research.

Contribution to the New York Climate Report

This research will be supplied as a contribution to the Water Sector of Climate Change and a Global City: An Assessment of the Metropolitan East Coast Region. This is a major project which comprises one of the regional components that contribute to the ongoing U.S. National Assessment: The Potential Consequences of Climate Variability and Change. The study is being conducted by NASA/GISS and Columbia University under the supervision of Cynthia Rosenzweig (PI) and William Solecki (Co-PI).

Education Product

The research methodology developed for this study will be utilized in the Remote Sensing for Studying the Environmental Effects of Land-Use/Land Cover Changes in Watershed Areas course to be offered by the civil engineering department at CCNY during years 1 and 2 of the NASA/PAIR initiative.