Wednesday, September 22, 2010

Desert dust reduces river flow

Environmental Research Web: Dark-colored dust that settles on snow in the Upper Colorado River Basin makes the snow melt early and robs the Colorado River of about 5 percent of its water each year, says a new study coauthored by researchers from the Cooperative Institute for Research in Environmental Sciences (CIRES), a collaboration of the University of Colorado and NOAA. This quantity of lost water is nearly twice what the city of Las Vegas uses in a year, says study coauthor Brad Udall, director of the Western Water Assessment (WWA) – a joint program of CIRES and NOAA.

"By cutting down on dust we could restore some of the lost flow, which is critical as the Southwestern climate warms," Udall said.

Snow dusted with dark particles absorbs a greater fraction of the Sun's rays and melts faster than white snow, said coauthor Jeffrey Deems of WWA and CIRES' National Snow and Ice Data Center (NSIDC). Earlier snowmelt then lets the growing season of snow-covered vegetation start earlier and more water is lost through evaporation and transpiration, he said. That leaves less water for the Colorado River, which supplies water to more than 27 million people in seven states and two countries.

Heavy dust coatings on the snowpack are a relatively recent phenomenon. Since the mid-1800s onwards, human activities, such as livestock grazing and road building, have disturbed the desert soil and broken up the soil crust that curbs wind erosion. Winds then whip up the desert dust – from northwest New Mexico, northeast Arizona, and southern Utah – and drop it on mountains downwind that form the river's headwaters, Deems said.

"Dust can have an impact even when it's too sparse to notice," said study leader Thomas Painter, a snow hydrologist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. and an affiliate scientist of NSIDC. "But it can get to the point where it looks like cinnamon toast."…

An aerial section of snow-covered Rocky Mountain range. This image shows an ariel view of Mt. Princeton. Shot by Wing-Chi Poon, Wikimedia Commons, under the Creative CommonsAttribution-Share Alike 2.5 Generic license

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