Desert Dust Intensifies Summer Rainfall in U.S. Southwest


DOE scientists at Pacific Northwest National Laboratory found that dust kicked up from the desert floor acts like a heat pump in the atmosphere, fueling the annual climate system called the North American Monsoon (NAM). NAM occurs during June, July, and August over the U.S. Southwest and northern Mexico and is characterized by surface heat and episodes of heavy rainfall. The region receives over 70 percent of its annual precipitation during these three months. The researchers used sophisticated simulation techniques to investigate the effect on the atmosphere of dust emitted from U.S. Southwest deserts to fuel the intensity of the monsoon system. The study simulated 15 years with dust emissions and 15 years without dust emissions, using the regional model WRF-Chem for the time period from 1995-2009, and compared the results with surface mass and satellite and surface aerosol optical depth observations. The enhanced dust increases precipitation by up to 40 percent during the summer rainy season in Arizona, New Mexico, and Texas. The study, the first on the U.S. Southwest summer monsoon, found that the heat pump effect is consistent with how dust acts on West African and Asian monsoon regions. Understanding how dust contributes to atmospheric heating is important for predicting drought and rainfall patterns throughout the world.

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Zhao, C., X. Liu, and L. R. Leung. 2012. “Impact of the Desert Dust on the Summer Monsoon System over Southwestern North America,” Atmospheric Chemistry and Physics 12, 3717-3731. DOI: 10.5194/acp-12-3717-2012.