Dust on snow

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From the Summit County Citizens Voice (Bob Berwyn):

Reducing dust deposition could help boost the Colorado River’s yield, but that would mean changing land-use patterns and human disturbances in the southwestern desert regions, according to Brad Udall, director of the Western Water Assessment. “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 Jeffrey Deems, who does research for the Western Water Assessment and the National Snow and Ice Data Center. Earlier snowmelt then lets the growing season of snow-covered vegetation start earlier, resulting in more water lost through evaporation and transpiration, Deems said 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 downwind on the mountains that feed the Colorado’s headwaters.

More coverage the Fort Collins Coloradoan (Bobby Magill):

With climate change factored in, the Colorado River could see a reduction in flow of up to 25 percent by 2050, said study co-author Brad Udall, director of the Western Water Assessment, a joint program of the National Oceanic and Atmospheric Administration and CU’s Cooperative Institute for Research in Environmental Sciences.

Each year, dust is carried by strong winds from Southwest deserts and deposited onto the snowy slopes of the Rockies. Much of that dust is seen in the San Juan Mountains, but some makes it as far northeast as the northern Front Range, Udall said Tuesday. Mountain snow can appear red or look like cinnamon toast after a dust storm, and it can easily be seen from an airplane…

The study, he said, does not directly address how the river’s flow will be decreased by climate change, but global warming is expected to dry and warm the region and reduce the Colorado River’s flow by up to 20 percent. That should be a concern to people living along the Front Range, because much of their water supply comes from the Colorado River Basin, he said. The loss of Colorado River flow and future development in the Front Range urban corridor are intrinsically linked, he said.

The study was published in the Sept. 20 issue of the Proceedings of the National Academy of Sciences and was paid for by the National Science Foundation, NASA and the Western Water Assessment.

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