Social-economic preparations for future climate change require geographically more detailed projections than global climate models can provide. Over the Greater Horn of Africa (GHA), this is particularly important because of the presence of complex regional orography, large inland lakes such as Lake Victoria, and highly diverse land surface conditions. We have adopted the regional climate modeling approach to downscale present (RF, 1961-1990) and a future (IPCC-A2, 2071-2100) climates generated by the NASA Finite Volume General Circulation Model(FvGCM). The RegCM3 regional climate model is coupled to a one-dimensional lake model which permits realistic vertical diffusion of heat energy.

We have conducted two pairs of thirty-year RegCM3 RCM simulations. The first pair (outer domain) has resolution of 40km with lateral and boundary conditions for RF and A2 constructed from the corresponding FvGCM runs. The second pair of RegCM3 downscaling simulations derive their lateral and boundary conditions from the 40km (outer domain) pair of simulations. The outer domain encompasses the countries of Burundi, Ethiopia, Kenya, Rwanda, Somalia, Sudan, Tanzania and Uganda, while the inner domain primarily corresponds to the country of Kenya.

The RegCM3 model results are compared with the results from our recent studies (Schreck & Semazzi, 2004; and Bowden et al, 2007) which utilize empirical analyses of the GHA regional climate variability. These results have unveiled a new mode of climate variability for the GHA region with temporal evolution consistent with the well-known trend associated with global warming. Over the GHA region the pattern for this mode consists of a dipole with the region of increasing rainfall centered over the Ethiopian Highlands and the corresponding region of decreasing rainfall centered over Tanzania. Other, salient features of the model simulations results are examined in this study.