Numerical studies of wet versus dry soil regimes in the West African Sahel

The West African Sahel lies between the wet, humid equatorial zone of Africa to the south and the Sahara Desert to the north. This topography results in a strong north-south precipitation gradient. A coupled land-atmosphere (cloud resolving) model and observed data from the Hydrological Atmospheric Pilot Experiment in the Sahel were used to simulate both wet and dry soil moisture regimes. There are two case studies-one characterized by convective precipitation, the other by fair weather. In both of the case studies, evapotranspiration from the tiger bush land cover was noticeably larger in the wet soil moisture regime. The increase in latent heat flux was the key factor in creating a boundary layer that was more favorable to late-afternoon deep convection in the wet regime. Differences in boundary layer growth and development between the case studies suggested a more important role for the land surface in fair weather environments versus convective precipitation environments.