In the West-African Sahel, extreme rainfalls are becoming more intense

The Sahelian rainfall regime has a well tempered character : the glitz of the 1950s and 1960s was followed by a drought of unprecedented magnitude in the world in the 20th century, impacting the region for more than twenty years. Over the past 35 years, annual rainfall has gradually increased, but something has changed : "it never rains but pours"..

In this study we attempted to find out whether "extreme" rainfall events have undergone significant changes during this recent period, based on a regional database of ground observations. While few stations show a significant trend, the statistical framework used allowed us to state that the region as a whole, which extends from the Senegalese coast to the shore of Lake Chad, shows a statistically significant increasing trend. This increase, of 5%/decade, concerns the mean and variability of rainfall extremes. In concrete terms, this means that the frequency of the rarest (strongest) events is increasing faster : whereas an event that had an average of 1 chance in 10 of occurring every year now occurs 1 year in 5 (i.e. a doubling of its frequency), a centennial event at the beginning of the period (1 chance in 100 of occurring every year) now occurs every 40 years (i.e. a frequency multiplied by 2.4).

These figures differ from the trends observed in the past and show the high sensitivity of Sahelian rainfall extremes. Although they have not been attributed to human activities, the question arises as to how to integrate this new hydro-climatic situation into development and climate change adaptation policies.

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Guillaume Chagnaud IGE
Article : https://iopscience.iop.org/article/10.1088/1748-9326/ac4a9c