From Wired
By Alexis Madrigal

A water crisis in the Western United States is primarily due to manmade global warming, and it could force difficult choices for the region as farmers, residents and biofuel producers fight for their share of water.

Sixty percent of the changes in the West’s water cycle are due to increased atmospheric greenhouse gases, write scientists in a paper published Thursday in Science. Small increases in winter air temperature, the research found, reduce the amount of snow falling in mountains. In turn, snow packs that previously acted as time-release water storage provide less water as they melt in the spring.

“In a place like California, the snow pack is going away or melting earlier. We don’t have enough dams to catch it all so we have to let it go out to the ocean,” said Tim Barnett, a research physicist at Scripps Institution of Oceanography and the study’s lead author. “All of our infrastructure has been set up to take advantage of climate the way it was, but things are changing.”

The new research comes as Western states are already struggling to supply water for both their farms and cities. Increased migration to the water-poor regions of the Southwest into cities like Los Angeles, Phoenix and Las Vegas has increased the amount of water necessary to support the rising U.S. population. With such a constrained supply and rising demand, the cost of water is likely to rise, experts said. Some California farmers, responding to a record water shortage, are even beginning to consider selling their water rights, instead of their crops.

Barnett’s team worked with climate models to simulate the impact of greenhouse gases on the Western water cycle. If their models for the future prove as accurate as their modeling of the past, the paper predicts unprecedented water shortages.

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