NASA Funded Study Shows Desert Dust Cuts Colorado River Flow
Snow melt in the Colorado River basin is occurring earlier, reducing runoff and the amount of crucial water available downstream. A new study shows this is due to increased dust caused by human activities in the region during the past 150 years. The study, led by a NASA scientist and funded by the agency and the National Science Foundation (NSF), showed peak spring runoff now comes three weeks earlier than before the region was settled and soils were disturbed. Annual runoff is lower by more than five percent on average compared to pre-settlement levels.

The findings have major implications for the 27 million people in the seven U.S. states and Mexico who rely on the Colorado River for drinking, agricultural and industrial water. The results were published in this week's Proceedings of the National Academy of Sciences. The research team was led by Tom Painter, a snow hydrologist at both NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the University of California at Los Angeles. The team examined the impact of human-produced dust deposits on mountain snowpacks over the Upper Colorado River basin between 1915 and 2003. Studies of lake sediment cores showed the amount of dust falling in the Rocky Mountains increased by 500 to 600 percent since the mid-to-late 1800s when grazing and agriculture began to disturb fragile but stable desert soils.

The team used an advanced hydrology model to simulate the balance of water flowing into and out of the river basin under current dusty conditions and those that existed before soil was disturbed. Hydrologic data gathered from field studies funded by NASA and NSF and measurements of the absorption of sunlight by dust in snow were combined with the modeling. More than 80 percent of sunlight falling on fresh snow is typically reflected back into space. In the semi-arid regions of the Colorado Plateau and Great Basin, winds blow desert dust east, triggering dust-on-snow events. When dark dust particles fall on snow, they reduce its ability to reflect sunlight. The snow also absorbs more of the sun's energy. This darker snow cover melts earlier, with some water evaporating into the atmosphere.

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