Atmospheric Dynamics of Extreme Precipitation over the West African Sahel

The period of the 70s and 80s was marked by a drought in the Sahelian countries. However, since the beginning of the 21st century, these countries have experienced a resurgence of heavy rainfall and devastating floods, causing inestimable socio-economic damage and losses. The objective of this work is to study the dynamics of atmospheric conditions associated with seventeen extreme rainfall events listed in the database of the Directorate of Civil Protection of Senegal and having caused significant socio-economic impacts between 2000 and 2017. This study was carried out using satellite products and atmospheric reanalysis data. The results of the analyses of the various atmospheric parameters studied show, at the synoptic scale, that extreme rainfall events are mainly modulated by African easterly waves. Strong moisture transport convergences in the lower tropospheric layers due to vortices associated with these waves are recorded. A response of this moisture convergence in the lower layers accompanied by vertical moisture transport is highlighted by strong anomalies and wind divergence. This configuration corresponds to the presence of a vertically well-structured convective system. The analysis of atmospheric parameters such as relative vorticity, wind, relative humidity and precipitable water shows that they are good indicators to characterize rainfall extremes. The behavior of the anomalies of these variables shows the presence of a significant amount of moisture in the tropospheric column and the most marked pressure levels are between 850 and 700-hPa, and in the upper layers around 200-hPa.