Evaluation of Sahel ground climatology using an off-line version of the SSiB vegetation model: focus on August

The Sahel has experienced a severe and persistent drought since the beginning of the 1960s. One of causes proposed to explain this dramatic trend includes the land use change, e.g. the land-surface degradation associated with human pressure that dramatically increased during this period. Because of the strong social, economic impacts, a number of studies with different models have been conducted to study the role of biosphere feedback of the Sahel drought of the past 20 years. Following these studies, this work evaluates the ground climatology of this region over the 1982-90 period, using observational precipitation data, satellite derived LAI, and an offline version of the SSiB land surface model. This paper discusses the seasonal and interannual variability of surface water and energy balances in West Africa. The spatial and temporal patterns of surface fluxes are analyzed. In addition, a comparison is made with reanalysis variables to evaluate the coherence of these two products. Moreover, correlation analyses are done with the main SST signals in the Pacific and Atlantic oceans and LAI data. To investigate the impact of land surface degradation in West Africa, sensitivity experiments are conducted. They are performed separately on the Sahel zone and Guinea zone and focuses on the impact of land cover change on water and energy balances in the west and east parts of each zone. These experiments show the importance of the modification of the land surface characteristics on the land surface-atmosphere relationship.