By Sid Perkins
If climate changes as expected, and future water use goes unchecked, there’s a 50 percent chance that Lake Mead—one of the southwestern United States’ key reservoirs—will become functionally dry in the next couple of decades, a new study suggests.
Besides providing water for millions, flow from Lake Mead—the reservoir formed as the Colorado River collects behind Hoover Dam—generates prodigious amounts of hydroelectric power. Over the past century, on average, about 18.5 cubic kilometers of water flowed into Lake Mead each year, says Tim P. Barnett, a climatologist at the Scripps Institution of Oceanography in La Jolla, Calif. Of that amount, about 2.1 km3 evaporate into the dry desert air or soak into the ground beneath the lake each year. What’s left in the lake is more than spoken for: The amount of water drawn from Lake Mead this year to meet demand in cities as far-flung as Los Angeles and San Diego will exceed 16.6 km3.