Differences in the Seasonality of Wind Erosion and Wind Erosivity across the Sahel

Semi-arid regions experience wind erosion, a major phenomenon in such areas, that can affect mineral dust emissions and soil fertility. So far, Sahelian aeolian erosion or erosivity have been monitored mainly in the Central Sahel (Niger and Mali). In the framework of the ENCAS (Erosion éolienNe en zone de Culture d'Arachide au Sahel) project, we monitored the number of saltating particles and the horizontal flux of aeolian sediment in Bambey (Senegal) since February 2020. We analyze these measurements along with long-term 5-minutes wind measurements (2014-2021) made at the neighboring INDAAF (International Network to study Deposition and Atmospheric composition in Africa) station. As a result, it appears that the seasonality of wind erosivity largely differs between Western Sahel and Central Sahel. In Western Sahel, wind erosivity is mostly due to wind speeds slightly above the wind speed erosion threshold during the dry-season, whereas in Central Sahel it is mostly related to high wind speeds largely above the threshold, that occur at the beginning of the rainy-season and are due to Mesoscale Convective Systems. Finally, the horizontal flux of aeolian sediments that was measured during the dry-season (resp. rainy-season) is of the same order (lower) in Senegal as (than) in Western Niger, and lower than in Eastern Niger. Altogether, annual aeolian flux are thus significantly lower in Western than in Central Sahel.