Tropical Waves Are Key Drivers of Extreme Precipitation Events in the Central Sahel

Abstract

Extreme precipitation events (EPE) are often associated with severe floods and significant damages in Central Sahel. To better understand their formation and improve their forecasts, we investigate the sub-seasonal drivers of EPEs. A composite analysis reveals that moist, cyclonic and upper-level divergence anomalies are found on average as a result of several tropical waves. The equatorial Rossby wave (ER) dominates at large scale providing a moist and convectively-active anomaly over the northern Sahel together with a smaller-scale African Easterly Wave (AEW). The Madden-Julian Oscillation provides upper-level divergence anomalies and a Kelvin wave increases convection during the EPE. Statistics show the prevalence of AEW and emphasize ER as a key driver of EPE. The co-occurrences of several tropical waves, especially those involving AEW, ER, and Kelvin waves, increase the probability of EPE. Monitoring these tropical waves combinations could improve EPEs forecasts.