THE INFLUENCE OF LAND-SURFACE PROPERTIES ON SAHEL CLIMATE .2. AFFORESTATION

A numerical experiment was performed to explore the nature of and mech anisms for the effect of large-scale afforestation in the sub-Saharan area on the climate. This sensitivity study, which consists of several short-term integrations of a climate model, suggests that afforestati on would enhance the rainfall in the region and would have the largest impact during dry years. While the rainfall increased in the afforest ation area, it decreased to the south of that region. It was found tha t this land surface change altered the surface energy balance and indu ced a circulation change that led to a change in rainfall. The influen ces of different vegetation species and the extent of the afforestatio n area on the rainfall were tested and are discussed. Reducing the aff orestation area by about 50% still resulted in a positive simulated ra infall anomaly. A detailed analysis of the surface energy balance is p resented. A comparison between the effects of afforestation and desert ification is also made.