A GCM study of climate change induced by deforestation in Africa

In this modeling study we investigated the potential climate change which would result from totally clearing the tropical rain forests in Africa. The primary research vehicle in our investigation was the standard version of the National Center for Atmospheric Research (NCAR) CCM3 global climate model (GCM), with a horizontal resolution of triangular spectral truncation T42 (approximately 2.8 2.8). Two separate 10 yr simulations were performed; for each of these the global climatological sea surface temperature field was prescribed. The purpose of the 10 yr simulations was to provide a sufficiently large ensemble whose average minimizes model noise errors. In the control simulation normal vegetation was prescribed. The design of the anomaly experiment was similar to the control run except that the tropical rainforest regions in Africa were replaced by savanna grassland vegetation. The CCM3 GCM successfully simulated the primary features of the seasonal mean climate conditions over Africa. The model results show that replacement of tropical rain forest vegetation with savanna grassland vegetation produces the following climate changes over Africa: (1) Over the deforested region, the model results indicate a significant reduction in areaaveraged rainfall throughout the year. The decrease ranges between 2 to 3 mm d -1 during the northern hemispheric summer months, when the region experiences the driest conditions (July to September), and less than 1 mm d -1 during the wettest months (autumn and spring). (2) Over southern Africa deforestation results in substantial rainfall reduction over Mozambique and rainfall increase over Botswana, Zambia, the southern region of the Democratic Republic of the Congo, and parts of South Africa. Changes in the trapped Rossby wave train activity generated by the mid-tropospheric latent heating over the tropical forest region are responsible for the continental-scale teleconnection climate response. (3) Over Eastern and Western Africa the impact of deforestation is primarily characterized by a reduction in rainfall, however the adopted GCM T42 resolution may not have been adequate to resolve the large contrasts in terrain and vegetation types. (4) Over the rest of Africa the response is relatively weak.