THE ROLE OF VEGETATION IN THE DYNAMICS OF WEST-AFRICAN MONSOONS

The focus of this paper is the role of meridional distribution of vege tation in the dynamics of monsoons and rainfall over West Africa. A mo ist zonally symmetric atmospheric model coupled with a simple land sur face scheme is developed to investigate these processes. Four primary experiments have been carried out to examine the sensitivity of West A frican monsoons to perturbations in the meridional distribution of veg etation. In the control experiment, the authors assume a distribution of vegetation that resembles the natural vegetation cover in West Afri ca. Each perturbation experiment is identical to the control experimen t except that a change in vegetation cover is imposed for a latitudina l belt that is 10 degrees in width. The results of the numerical exper iments demonstrate that West African monsoons and therefore rainfall d istribution depend critically on the location of the vegetation pertur bations. Changes in vegetation cover along the border between the Saha ra desert and West Africa (desertification) may have a minor impact on the simulated monsoon circulation. However, coastal deforestation may cause the collapse of the monsoon circulation and have a dramatic imp act on the regional rainfall. The observed deforestation in West Afric a is then likely to be a significant contributor to the observed droug ht.