Periods of drought in the western United States have become longer over the past 50 years, according to a new study.
In hopes of understanding how significantly rainfall totals and timing have changed in the past five decades, researchers analyzed daily meteorological data from over 300 long-term weather stations across the western US.
“In the West, total annual rainfall has decreased by about 0.4 inches since the 1970s. The average longest dry period has increased by roughly 50% from 20 to 32 days,” says co-senior author William K. Smith, assistant professor in the School of Natural Resources and the Environment at the University of Arizona.
The new study reports ominous trends for the desert southwest, including southern California, Arizona, and New Mexico, regions that already experience relatively high mean temperatures and lower annual water inputs, such as rainfall or snowfall. For these regions, substantial multi-decade evidence demonstrates droughts are becoming longer and more frequent.