Feb 4, 2016

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

Prein, Andreas F., Holland, Gregory J., Rasmussen, Roy M., Clark, Martyn P., Tye, Mari R.
Geophysical Research Letters

"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