In the last century, aeolian erosion in the Sahel has fluctuated significantly, in connection with irregular precipitation and variability of the vegetation cover and an increasing anthropogenic pressure. In the dry season, the Harmattan flow transports large amounts of mineral dust emitted from Saharan sources. In the wet season, very high surface wind speeds associated with convective systems produce intense local dust emissions. The Sahel region is thus a region of emission and deposition of mineral dust. A precise estimation of the net mass budget of mineral dust requires to account for the strong inter-annual variability of the dust atmospheric load in this region.

Since 2006, a set of stations dedicated to the monitoring of mineral dust are operating in the Sahel as part of the INDAAF network. Simple and robust instrumentation allows to monitor simultaneously the atmospheric dust load, the concentration of particles smaller than 10 µm, the total and wet deposition fluxes.

The dust concentrations, the aerosol optical depths and the deposition fluxes all exhibit persistent seasonal cycles. The variability of the dust concentrations is driven by the variability of the dust transport in the Harmattan season and by local dust emissions in the Monsoon season. The seasonal cycle of the dust AODs is impacted by the variability of the dust layers thickness and altitude. The seasonal cycle of the deposition fluxes is very sensitive to the contribution of the wet deposition.

From these results, it is clear that reproducing simultaneously the dust concentrations, AODs and deposition fluxes in the Sahel is a challenge for regional models. The data from the Sahelian INDAAF stations will be used as validation data sets in the frame of the European DUSTCLIM project (ERA4CS) to evaluate long-term regional dust simulations and to estimate the benefit brought by the assimilation of satellite data.