Now, the record shows that they’re occurring more and more frequently, and may continue to increase as the climate keeps warming. The study’s authors suggest that climate warming in the desert region just south of the Sahel has caused changes in wind patterns over northern Africa that have affected the formation of these storms.
“This observation is clear evidence of a variation in weather patterns, and is likely to be related to climate change,” said Chuntao Liu, an atmospheric scientist at Texas A&M University who was not involved with the new research, in a comment on the study that was also published Wednesday in Nature.
The findings are a concern for the area’s inhabitants for several reasons. Intense storms can cause serious damage to infrastructure. And the region’s changing precipitation patterns could also post a threat to agriculture, according to the study’s lead author, meteorologist Christopher Taylor of the Centre for Ecology and Hydrology in the United Kingdom. Large storms can cause nutrient-rich soil to erode, potentially reducing the landscape’s fertility, he said.
The researchers focused on a kind of large storm, common in the Sahel and other tropical parts of the world — as well as in the U.S. Great Plains, Taylor noted — called a mesoscale convective system. It’s essentially a large, intense thunderstorm.
“They’re rather complex storms,” Taylor told The Washington Post. “If you thought of them like some kind of engine feeding on the fuel of humidity in the atmosphere, they’re very efficient at extracting that fuel and producing intense rain.”
Examining satellite records from 1982 through 2016, the researchers found more than a threefold increase in the frequency of large storms — which Taylor said can extend up to nearly 10 miles above the ground — over the course of the study period. The researchers also found that these increase tracks strongly with a warming trend in the Sahara.
The Sahel, itself, hasn’t been seeing a particularly notable increase in temperature in recent years. But the Sahara region just to the south is one of the world’s most rapidly warming places, besides the Arctic, Taylor noted.
As a result, there’s been a stark change in the temperature gradient across the region of Africa spanning the Sahel — and the scientists believe that this effect has caused a change in certain specific types of wind patterns that are known to strongly influence the formation of thunderstorms.
“They argue that this warming has led to increased convection through enhanced wind shear (the difference in wind speed over a relatively short distance, either vertically or horizontally, in the atmosphere) and changes to the Saharan air layer,” explained Liu in his comment. “These are reasonable speculations that could probably be validated using simulations of the regional climate.”
The effect of temperature changes on wind patterns has been widely discussed by climate and atmospheric scientists looking at different parts of the world. Changes in temperature in specific regions can alter the thickness of the atmosphere in those places, which can affect the way air moves from one part of the world to another. Some scientists have speculated, for instance, that rapid warming in the Arctic may be causing changes in the North Atlantic jet stream.
Still, there’s more work to be done before anyone can say for certain what’s been going on with the Sahelian storms. Current models don’t fully account for all the atmospheric processes that cause these systems to form, Taylor said, and they haven’t actually been able to reproduce the increase in frequency that the observational record has revealed.
The researchers and colleagues at the UK’s Met Office, its national weather service, are currently collaborating on a project they hope will produce “much more detailed computer simulations in which we can simulate the dynamics of these weather systems much better,” Taylor said. “And we’re looking to see what those simulations will tell us in a world with increased greenhouse gases.”
But for now, he said, scientists are fairly confident that the Sahara will continue to warm at a faster pace than the rest of Africa.
“So our best guess is that this will continue to provide more and more favorable conditions for the most intense storms to develop.”