Water Resources in Rockland - Planning in a Changing World

Climate Change and Water Supply

icebergWhile virtually all climate models forecast a considerably warmer climate (5-11°F) for New York State in 2100, predictions of precipitation or the more relevant parameter 'precipitation-evapotranspiration' are much less certain. There is widespread agreement that the region will experience more extreme flooding and drought events and that sea level rise (up to 2 ft by 2100) will increase the salt concentration of the Hudson River.

Climate models predict a 5-11F° (3-6°C) warmer climate in the region by 2100 (relative to 1980-99; IPCC, 2007 and NASA/GISS, 2000). This will result in increased evapotranspiration, more heat waves in the region, and more frequent extreme events such as flooding, droughts, and reduction in snow-on-the ground-days.


It is much less certain by how much precipitation will increase (or decrease). According to the IPCC, winter precipitation will increase, but no prediction is made for summer precipitation. Even if precipitation increases, increased evapotranspiration might lead to decreased availability of 'net' water (Precipitation-Evapotranspiration). It will take a few more years until climate models are at the stage where regional precipitation forecasts can be made with a high level of confidence.

The current rate of sea level rise (0.12 in/y or 0.3mm/y for 1993-2003) is likely to increase in the 21st century, resulting in levels of up to 2ft (60cm) higher than today by 2100. The salt concentration in the Hudson is a combination of sea level rise pushing more salt upstream and a potentially wetter climate increasing discharge rate and therefore pushing the salt back out towards the sea. An increase in severe droughts would make it likely that salt concentrations in the Hudson River would increase during these critical periods.

Adapting to Climate Change in Long-Term Water Planning

Efforts are underway in London, New York City, Halifax and Toronto to consider climate change adaptations. New York City established a Climate Change Task Force in 2004 which has since evolved into an agency-wide Climate Change Program to make sure that the New York City Department of Environmental Protection's strategic and capital planning efforts take into account the possible effects of climate change on NYC's water supply and other infrastructure systems.

As the base for its efforts NYC reviewed regional projections from five global climate models and three different emissions scenarios and summarized the results with respect to air temperature, precipitation and sea level (see Climate Change Science, Observations and Projections, p. 10).

While the long-term trends in precipitation are up, the seasonal distribution and the net of precipitation minus evapotranspiration will determine the effect on future drought frequency. While the global climate models don't predict evapotranspiration they do provide projections by month and the results of that analysis will be shown here when complete.

New York City has set out a climate change plan with five tasks:

  1. Working with climate scientists to improve regional climate change projections
  2. Quantify potential climate change impacts on NYC water systems
  3. Determine and implement appropriate adjustments to NYC's water systems
  4. Inventory and reduce greenhouse gas emissions
  5. Improve communication and tracking mechanisms

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