Future Dry Spells in the Southwest US Aggravated by Climate Warming (Invited)

The early 21st century drought is an example of the kinds of droughts the Southwest United States is prone to. Such droughts tend to take on large southwest footprints, although both observations and climate model simulations display different degrees of dryness in California, the Great Basin, and the Colorado basin. The early 21st century drought has been more severe in the Colorado basin than in California. As quantified by the VIC hydrological model, the historically most extreme droughts have tended to build up and finally abate over an extended multiyear period. Especially during the early 21st century, observed Southwest droughts have been exacerbated by anomalously warm summer temperatures. This tendency may continue—several different 21st century climate model simulations suggest that dry years will experience anomalously warm summer temperatures. These severe future droughts are aggravated by enhanced, globally warmed temperatures that reduce spring snowpack and late spring and summer soil moisture. As the climate continues to warm, soil moisture deficits accumulate beyond historical levels, indicating there could be larger reductions in runoff in the Colorado and other key basins of the Southwest.