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Science News Online
Week of Feb. 23, 2008; Vol. 173, No. 8
Going Down: Climate change, water use threaten Lake Mead
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.
[IMAGE] BATHTUB RING. Water levels in Lake Mead have dropped
significantly in recent years, as chronicled by the white mineral
deposits on rocks that were formerly submerged.
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.
And the situation will likely get worse, Barnett and colleague David
W. Pierce speculate in an upcoming Water Resources Research. By 2030,
the researchers note, annual demand for Lake Mead's water is
projected to rise to 17.4 km3. Also, some climate studies suggest
that the Colorado's flow will drop between 10 and 30 percent in the
next 30 to 50 years. Using these data, as well as weather simulations
that impose random but reasonable annual variations in river flow
volume, Barnett and Pierce used a computer model to estimate the
remaining useful life of the Lake Mead reservoir.
Thanks in part to the worst drought in the Southwest in the past 500
years (SN: 6/26/04, p. 406), Lake Mead is now at about 50 percent
capacity. If current allocations of water persist, there's a 50
percent chance that by 2023 Lake Mead won't provide water without
pumping, and a 10 percent chance that it won't by 2013. Moreover,
there's a 50 percent chance that Hoover Dam won't be able to generate
power by 2017, the researchers estimate.
"We were stunned at the magnitude of the problem and how fast it was
coming at us," says Barnett.
Results of the new study are "fairly provocative, an eye-opener,"
says Connie Woodhouse, a climatologist at the University of Arizona
in Tucson. Using estimates of river flow based on an average of the
past century may be optimistic, she adds, because tree
ring–based reconstructions of the region's climate suggest that
the 20th century was one of the wettest in the past 500 years. "The
more we learn about the Colorado River and its hydrology, the more
worried we need to be," says Peter H. Gleick, a hydrologist at the
Pacific Institute in Oakland, Calif.
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Barnett., T.P., and D.W. Pierce. In press. When will Lake Mead go
dry? Water Resources Research.
Perkins, S. 2007. Tree rings tell tale of megadroughts. Science News
171(June 23):397. Available to subscribers at
______. 2004. Long dry spell. Science News 165(June 26):406.
Available to subscribers at
Tim P. Barnett
Mail Code 0224
Scripps Institution of Oceanography
University of California, San Diego
9500 Gilman Drive
La Jolla CA, 92093
Peter H. Gleick
654 13th Street, Preservation Park
Oakland, CA 94612
University of Arizona
Department of Geography and Regional Development
412 Harvill Building, Box #2
Tucson, AZ 85721-0076
From Science News, Vol. 173, No. 8, Feb. 23, 2008, p. 115.
Copyright (c) 2008 Science Service. All rights reserved.
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