THE IMPACTS OF CLIMATE CHANGE ON U.S. WATER SUPPLY

The initial reports of the Intergovernmental Panel on Climate Change and those that have followed have consistently concluded that our global climate is changing. A report from the National Research Council in June of 2006 concluded that recent decades are warmer than any in the past 400 years and potentially warmer than any in the last several millennia and that human activities are responsible for much of the recent warming. These reports and others indicate that one of the most important impacts of climate change is on the world's water supplies. Not all regions will be impacted equally, however, with some regions experiencing particularly negative effects, while other areas may actually benefit from climate change. Water supply impacts on U.S. water resources are expected to be most profound in the west, where the runoff cycle is largely determined by snowmelt. Studies to date indicate that the effects of warmer climates on the seasonality of runoff in such regions will likely shift the spring and summer melt earlier in the year and that drought periods will be more intense and extended. Water supplies can also be impacted by flood events, and recent record floods across the American east may well be an indicator of changes to come. This paper begins with a summary of the results from a series of studies from the northwestern U.S. that explore the potential impacts of climate change on municipal water supplies. These studies use a series of loosely-linked models to assess potential impacts. In the studies, the output from global circulation models are spatially and temporally downscaled to serve as inputs to a distributed hydrology models that estimate future, climate impacted streamflows. These inflows are then used to evaluate future system vulnerability. The impacts of climate change on water demand are explored. The case studies include the cities of Portland and Seattle, among others. In addition, the impacts of climate change on fishery resources is explored. An example of the potential impacts of climate change on Chinook salmon production, in the Snohomish River basin, is presented. The paper addresses water supplies in the eastern US. Potential impacts on urban water supplies in the east are explored including the water supplies of the Washington, D.C. and the Atlanta metropolitan areas.