Everyone is talking about how climate change is influencing weather patterns in the Atlantic, where several intense hurricanes have wreaked havoc in Texas, Florida, Puerto Rico, and the U.S. Virgin Islands. But what about drylands? Does climate change affect them, too?
Researchers at the Universities of Cardiff and Bristol in the U.K. studied more than 50 years of detailed rainfall data from a semi-arid drainage basin in southeastern Arizona. What they found was that although there was an increase in total rainfall, there has been a long-term decline in heavy rainfall events. So: fewer monsoons, and more small storms, delivering less rain.
The interesting thing about the researchers’ findings is that it goes against commonly held assumptions about rainfall trends under climate change.
“In drylands, convective (or short, intense) rainfall controls water supply, flood risk, and soil moisture, but we have little information on how atmospheric warming will affect the characteristics of such rainstorms, given the limited moisture in these areas,” said study lead author Dr. Michael Singer of Cardiff University.
Co-author Dr. Katerina Michaelides of the University of Bristol said, “Our findings are consistent with previous research in the Colorado Basin, which has revealed a decline in runoff in the upper part of the Basin. Our work demonstrates that there is a more regional decline in water resources in this dryland region, which may be found in other dryland regions of the world.”
Because convective rainfall trends are not easily detected in daily rainfall records or well simulated by global or regional climate models, the researchers needed to create a new tool to assess the effects of climate change on rainfall patterns in drylands.
Their model, STORM, simulates individual rainstorms and their expression over a river basin. It can also represent different classes of climate change over decades.
The researchers used STORM to show that historical rainfall trends likely resulted in less runoff from this dryland basin, and they expect that the same effect has occurred at many similar basins in the region.
“We see this model as a useful tool to simulate climate change in regions and cases where traditional models and methods don’t capture the trends,” said Singer.
Photo: Monsoon rains in the desert near Tucson, Arizona. Credit: Shutterstock