Climate Change Threatens Western States’ Water Supplies

by Tom Kenworthy

Western states that rely on snowpack for their water supplies are going to face a challenging future because of climate change, a senior Department of Interior official warned a Senate subcommittee Thursday.

“Warming and associated loss of snowpack will persist over much of the western United States,” Assistant DOI secretary Anne Castle said in her written testimony to the water and power subcommittee of the Senate Energy and Natural Resources Committee. A recent Bureau of Reclamation report, Castle said, has concluded that “this loss of snowpack storage is expected to result in a decrease in the amount of reliable water supply in areas where snow has been a major component of the hydrologic system.”

The Senate subcommittee hearing comes a week after the Global Climate Project reported that worldwide carbon dioxide emissions from the combustion of fossil fuels had risen by 5.9 percent in 2010, the biggest annual increase in history.


Climate change is already producing dramatic changes in the water cycle in the U.S., and more changes are coming, according to the U.S. Global Climate Change Research Program’s 2009 report on climate change impacts.

“Evidence is mounting that human-induced climate change is already altering many many of the exsiting patterns of precipitation in the United States, including when, where, how much, and what kind of precipitation falls,” the report says. And it predicts that “dry areas will become drier and and wet areas wetter,” with particularly severe effects in the Southwest which is expected to have more severe and more prolonged droughts.

A 2010 report prepared for the Natural Resources Defense Council concluded that one-third of U.S. counties, more than 1,100 in all — face greater risks of water shortages by 2050 as a direct result of global warming. The report says that 14 states, many in the Southwest and Great Plains, face extreme or high risks to their water supplies.

The impacts of these changes in water supply on the U.S. system of public lands — national parks, forests, rangelands and wildlife refuges — are expected to be significant. National Park Service Director Jon Jarvis, for example, has called climate change “the greatest threat to the integrity of our national parks that we have ever experienced.”

From sea level rise, to early snowmelt, to severe weather events, to elevated temperatures that affect where animals and plants can survive, the consequences of global warming on U.S. public lands are already widespread. Glacier National Park in Montana has already lost more than 80 percent of its namesake ice fields that were present in 1850, and the last of the 26 remaining glaciers may be gone by 2030 according to the U.S. Geological Survey.


“If we do not take action to slow or halt climate change now the future of our national parks will include the accelerated loss of glaciers at Mount Rainier National Park; the lost of Joshua trees at Joshua Tree National Park; and the submersion from sea level rise of Everglades National Park…” a report from the National Parks Conservation Association warns.

A critically important role for public lands is sustaining adequate water supplies and good water quality, a job that will grow more difficult with global warming. That won’t be just an aesthetic loss: A U.S. Forest Service report estimated the value of water that flows from our national forests at $4.3 billion a year.

Tom Kenworthy is a senior fellow at the Center for American Progress on the Public Lands team

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