Lake Mead has a 50 percent chance of running dry by 2021 — and a 10 percent chance of being dry by 2014 — because of current water consumption rates and the effects of global climate change, according to a research paper from two scientists at Scripps Institution of Oceanography in La Jolla.

That would imperil the Southwest’s water supply and electricity generation. The Colorado River, which feeds Lake Mead, is a major water source for San Diego and a large producer of hydroelectric power.

The Colorado River’s flow will decline as much as 30 percent over the next half century, say the researchers, David Pierce and Tim Barnett, at the same time that more people living in the Southwest will be relying on it. The researchers warn the Colorado River’s users — seven Western states, including California, and Mexico — to determine now how they will share less water in the future.

“We hope this work will spur solutions, as time is short,” they write in their draft report, submitted to the American Geophysical Union. “The alternative to reasoned solutions to the coming water crisis is a major societal and economic disruption in the desert southwest.”

The Scripps researchers say more water is being drawn out of Lake Mead, which is outside Las Vegas, than is filling it, the result of several factors. The growing population in Colorado, Wyoming and Utah is drawing more of the water it is entitled to from the river. And warmer temperatures attributable to climate change are reducing the snowfalls that feed the river.

The levels in Lake Mead have dropped as the Colorado River has endured a sustained eight-year drought. The massive reservoir is 50 percent full. As its levels have declined, the Hoover Dam’s hydroelectric production capacity has waned. The massive Nevada dam has lost almost a small power plant’s worth of energy production; its energy is used by 1.3 million people from Arizona and Nevada to Los Angeles.

The researchers say the lake’s levels have a 50 percent chance of dropping so low by 2017 as to prohibit hydroelectric power production.

“It seems clear that the threat to power production on the Colorado is both real and more imminent than most might expect,” they write.

ROB DAVIS

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