Human activities, such as livestock grazing and building, are breaking down desert soil in the Southwest, leaving dusty particles to be swept up by the wind. The wind eventually drops the dust on the snow-capped mountains of the Colorado River’s watershed. In areas where dark dust has settled, the snow turns pink, red, or brown.
Snow dusted with dark particles absorbs more sunlight and melts faster than white snow. Scientists conducting field studies in the Rocky Mountains can demonstrate the effect with a simple experiment. They scrape a small area of snow free of dust. When they come back a few hours later, the dusty snow surrounding the clean area has melted faster, leaving an elevated patch of white snow (seen in the photos above).
Dusty snow causes earlier melting, particularly in the spring and summer. Plants are uncovered earlier in the growing season, and water that would otherwise flow to the river evaporates from the leaves of growing plants instead. A new study reveals that this phenomenon robs the Colorado River of about 5 percent of its water each year. The lost water amounts to more than 250 billion gallons—nearly twice what the city of Las Vegas uses in a year.
Melting snow supplies more than 75 percent of the water in the Colorado River, which in turn supplies water to more than 27 million people in the United States and Mexico. Changes in the timing and amount of snowmelt can exacerbate problems with already limited water supplies.
Rising temperatures due to global warming are already leading to earlier melting of the snowpack in the western United States. Reducing soil disturbance in the desert Southwest could help extend the snowmelt season, offsetting some of the Colorado River’s projected water losses due to warming temperatures.
Photos courtesy of the Center for Snow and Avalanche Studies. Video produced by the Cooperative Institute for Research in Environmental Sciences (CIRES).