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Lake Mead, located in Nevada and Arizona, is a source of drinking water for millions of people in the southwestern United States.

Human demand, natural forces such as evaporation and human-induced climate change are creating a net deficit of nearly 1 million acre-feet of water per year from the Colorado River system, according to research marine physicist Tim Barnett and climate scientist David Pierce, both of the Scripps Institution of Oceanography.

If the Southwest experiences an unusually dry year or a sustained drought, water deliveries could become highly unstable and variable, the study says.

The study finds Lake Mead could run dry even if the Bureau of Reclamation goes ahead with proposed mitigation measures.

In their paper, "When will Lake Mead go dry?," Barnett and Pierce predict there is a 10 percent chance the reservoir will run dry by 2014. They also note there is a 50 percent chance that lake levels will drop too far to allow hydroelectric power generation by 2017.

"We were stunned at the magnitude of the problem and how fast it was coming at us," Barnett said. "Make no mistake, this water problem is not a scientific abstraction, but rather one that will impact each and every one of us that live in the Southwest."

Barnett also noted he and Pierce used conservative estimates in their study, meaning water shortages are likely to be even more dire than they forecast.

The University of California-San Diego, the Lawrence Livermore National Laboratory and the California Energy Commission supported Barnett and Pierce's research.