Running dry: The U.S. Southwest's drift into a drier climate state

"A normal year in the Southwest is now drier than it once was...If you have a drought nowadays, it will be more severe because our base state is drier...The weather types that are becoming more rare are the ones that bring a lot of rain to the southwestern United States...Because only a few weather patterns bring precipitation to the Southwest, those changes have a dramatic impact."

Andreas Prein, study lead-author and researcher at the National Center for Atmospheric Research (NCAR)

• Applies a weather type (WT) analysis to reanalysis data from 1979–2014 that characterize typical weather conditions over the contiguous United States
• Assigns precipitation trends within 1980–2010 to changes in WT frequencies and changes in precipitation intensities
• Shows that in the North Atlantic and Midwest region precipitation intensity changes are the major driver of increasing precipitation trends
• Finds in the U.S. Southwest, however, WT frequency changes lead to a significant precipitation decrease of up to −25% related to an increase in anticyclonic conditions in the North East Pacific
• States this trend is partly counteracted by increasing precipitation intensities