The response to deforestation and desertification in a model of West African monsoons

Since Charney proposed his theory on the dynamics of deserts and droughts in the Sahel [Charney, 1975], there has been significant scientific interest in the interaction between vegetation and climate in this region. The essence of this interaction is that the atmospheric circulation, and therefore rainfall, over this region may be sensitive to changes in vegetation cover near the desert border. Here we describe simulations of the West African monsoons with a simple zonally-symmetric model. The results suggest that the potential impact of human induced change of land cover on regional climate depends critically on the location of the change in vegetation cover. That is, desertification along the border with the Sahara (e.g., in Chad, Niger, Mali and Mauritania) leaves a relatively minor impact on monsoon circulation and regional rainfall; deforestation along the southern coast of West Africa (e.g., in Nigeria, Ghana and Ivory Coast) may result in complete collapse of monsoon circulation, and a significant reduction of regional rainfall.