SW Dust Reduces Colorado River Runoff
Dust generated in the deserts of the Southwest frequently lands in the mountains of Colorado, falling in the Colorado River watershed during the winter and coloring white snow a reddish brown. In a new study published in the Proceedings of the National Academy of Sciences, scientists modeled the impact of this dust deposition on Colorado River flow. They found that dust deposition can reduce runoff due to the effects of dust on snow albedo: the darker, dust-covered snow absorbs more sunlight, warming the surface and increasing snowmelt. The modeling results showed that with dust deposition, melting occurred three weeks earlier in the year. In the model, the earlier snowmelt leads to more evapotranspiration from exposed soil and vegetation, which reduces annual runoff in the Upper Colorado River Basin by about 5%. The source of all this dust is tied to intensified human land-use, such as grazing, which has led to a five-fold increase in dust in the West during the 19th and 20th centuries. These results indicate that land management practices aimed at reducing dust could be one way of alleviating projected declines in Colorado River flow in coming decades.