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The water supply sector report of the Metro East Coast Study assesses potential impacts of climate change on the New York City and related regional water supply systems and suggests types of adaptive measures that might be undertaken to cope with the effects of climate change. It is now generally assumed that global climate change is likely and that it will include temperature increases, changes in precipitation, and a significant rise in sea levels. These changes will have impacts both on demand and on supply in the New York City water supply system and other water supply systems in the region, including those of Long Island and the Delaware River downstream from New York City's reservoirs. While temperature increases and sea level rises are expected, there is a range of forecasts with respect to the timing and level of these variables. Moreover, forecast changes in regional precipitation vary widely, from positive in some GCMs to negative in others. Thus there is a substantial degree of uncertainty about climate change and its impacts on regional water systems. Urban water supply systems have large infrastructures, substantial customer bases, and long lead times for planning. Planning must therefore be a matter of considering what elements of the system might be impacted by global warming, what information will be needed to make adaptations, and what the timing of such adaptations should be. In most cases, both institutional and infrastructure responses will be required, for example in increasing the interconnectivity of regional systems.

Among the principal conclusions are:

  • Climate change projections indicate that the natural variability of the hydrologic systems in the region will increase, with potential increases in both floods and droughts.
  • Increased uncertainty will require a range of resiliency options from water management.
  • Ecosystem services are likely to be affected.
  • New York City's water supply systems should be able to cope with climate uncertainty over the very near term, but an effective planning process needs to be put in place in order to consider the adaptations that may be required in the future.
  • The implementation of institutional and infrastructure measures is likely to require long-term institutional commitments.
  • Interregional cooperation may offer opportunities to utilize water resources more efficiently.
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