Drought Persists in the U.S. Southwest
Persistent drought conditions have spread across the U.S. Southwest, with the Four Corners area of Arizona, Colorado, New Mexico, and Utah standing out as extremely dry. In early November 2018, more than 9 million people lived in areas of drought in those four states; another 6 million lived in abnormally dry areas, according to the National Integrated Drought Information System.
The map above shows drought conditions across the United States as of November 6, 2018. The data come from the U.S. Drought Monitor, a partnership of the U.S. Department of Agriculture, the National Oceanic and Atmospheric Administration, and the University of Nebraska-Lincoln. The map depicts areas of drought in progressive shades of orange to red and is based on measurements of climate, soil, and water conditions from more than 350 federal, state, and local observers around the country. (NASA provides experimental measurements and models to this drought monitoring effort.)
More than half the population in New Mexico and Arizona is located in drought-stricken areas. In Utah, the entire population is dealing with drought as the state experiences its worst drought in a decade.
According to the U.S. Drought Monitor, the Four Corners has been experiencing “extreme drought” conditions—potentially causing major crop losses and widespread water shortages and restrictions—since late January 2018. In April, drought conditions in certain areas intensified and have since persisted at the most severe level labeled “exceptional drought”—potentially leading to widespread crop losses and water emergencies. However, the 2018 drought conditions in this part of the country are only a snapshot of a long-term drought.
“This particular year is really just a continuation of a drought in that region that has been going on almost continuously since the late ‘90s and early 2000s,” said Ben Cook, a climatologist at NASA’s Goddard Institute for Space Studies. “Maybe once or twice a decade, you’ll get a single big drought year in much of the western U.S., but the really unusual part is how long the drought has been actually going on.”
Cook cites a few reasons for the prolonged drought conditions. A main driver has been relatively cold ocean conditions in the Eastern Tropical Pacific for the last couple of decades. As a result, winter storms that normally come to the U.S. Southwest and Mexico are getting pushed further north.
“Storms are not bringing in a lot of moisture, rain, and snow in the region,” said Cook, “and that means water that would be coming in and restoring the soil and snowpack is not available for the following growing season.”
Additionally, the last time the western United States had a drought this long or intense was in the 1950s, Cook said, when there were a lot less people. Not only has the population increased since then, but the southwest is also home to some of the fastest-growing large cities.
As a growing number of people depend on the Colorado River Basin for their water supply, two large reservoirs are on the brink of falling to levels that may spur a water shortage in Colorado River Basin states in 2020. Seven states—including the Four Corners—have drafted drought contingency plans to manage dwindling water levels in the Colorado River Basin.
Even if the region receives plenty of rainfall, warm temperatures may still affect the U.S. Southwest even after the drought passes.
“Independent of rain and snowfall in the region, we’re seeing the warmer temperatures associated with climate change are just drying things out regardless,” said Cook. “Eventually, we’ll return back to some kind of more ‘normal’ conditions, but even those conditions are likely to be drier than what we used to think of as ‘normal.’”
References & Resources
+ ABC4 (2018, September 12) Utah drought worst in ten years, prompting emergency action. Accessed November 8, 2018.
+ AZ Central (2018, October 10) Western states release proposed agreements for drought-stricken Colorado River. Accessed November 8, 2018.
+ National Integrated Drought Information System U.S. Drought Portal.
+ NASA Earth Observatory (2018, June 18) Intensifying Drought in the American Southwest.
+ U.S. Drought Monitor (2018, November 8) This Week’s Drought Summary. Accessed November 8, 2018.
+ United States Census Bureau (2017, May 25) The South Is Home to 10 of the 15 Fastest-Growing Large Cities. Accessed November 8, 2018.