Sahel is a semi-arid area south of Sahara in Africa. Most precipitation falls in the monsoon period from June to September. The area is often exposed to intense rainfall with a major impact on society.
When researchers have analysed satellite data from the western part of the Sahel area, they see that extreme storms are three times as frequent today compared to 35 years ago. The study is published in Nature this week.
“The threefold increase in frequency of extreme storms is linked to the anthropogenic warming of the Sahara desert. The horizontal temperature difference between the Sahara and the regions south of it has increased, which affects wind patterns in the area,” said Danijel Belusic, today researcher at SMHI Rossby Centre and one of the authors of the article published in Nature.
Temperature difference and winds
In an environment with sufficient heat and moisture, the intensity of large storms depends on the rate of increase of wind with height above ground. The increased horizontal temperature difference increases the vertical change of winds and consequently the intensity of the storms. This in turn brings more humid air higher up into the atmosphere in larger convective clouds. The increased vertical extent of the clouds provides the conditions for more extreme rainfall.
“The extreme events such as torrential rain and flooding are strengthening as the large storms become even more powerful. It of course has great impact in the region, particularly in urban areas that are vulnerable to large flooding events,” said Danijel Belusic.
Even more extreme future?
Climate models show that as the climate change continues, the temperature in the Sahara will further increase, and the temperature difference in the Sahel area may be even greater.
“So far, we have not seen any stagnation of temperature rise in the Sahara. If our theory is true that it is the temperature difference that intensifies the extreme storms and rainfall, then the extreme storms and the intensity of the precipitation over Sahel will continue to increase,” said Danijel Belusic.