Simulation of West African monsoon using RegCM3 Part II: impacts of deforestation and desertification

In this study, we investigate the feedback mechanisms between land cover and the monsoon in West African using the International Centre for Theoretical Physics Regional Climate Model (RegCM3). A series of multi-year simulations are performed using reanalysis boundary conditions under three idealised vegetation states (potential, desertified and deforested). The study shows that both desertification and deforestation tend to increase the monsoon flow over the Guinean region, although the mechanisms for change are different in each case. Desertification increases the flow mainly by increasing the meridional temperature gradient. While this reduces rainfall over the desertification region, it increases rainfall to the south. On the other hand, deforestation increases the monsoon flow mainly due to the reduced surface friction experienced by the flow over the Guinean region. This reduces rainfall over the entire West African region. The study further shows that desertification and deforestation also increase the speed and specific humidity of the mid-tropospheric easterly flow, to the south of the African easterly jet. Consequently, the flow transports more moisture away from the West Africa region at the expense of low-level moisture, resulting in less moisture available for rainfall over the region. Overall, this study suggests that the state of the biosphere in West Africa may play an important role in determining the characteristics of the monsoon and rainfall pattern.