Abstract:

Runoff fields over northern Africa (10-25°N, 20°W-30°E) derived from 17 atmospheric general circulation models driven by identical 6 ka BP climate forcing have been analysed using a hydrological routing scheme (HYDRA)to simulate changes in lake area. The AGCM-simulated runoff produced 6-fold differences in simulated lake area between models, although even the largest simulated changes considerably underestimate the observed changes in lake area during the mid-Holocene. Most of the inter-model differences in simulated lake area can be attributed to differences in the simulated precipitation (R2 =0.83). The higher correlation between runoff and simulated lake area (R2 =0.92) implies that simulated differences in evaporation have a contributory effect. When runoff is calculated using an offline land-surface scheme (BIOME3), the correlation between runoff and simulated lake area is (R2=0.94). Finally, it is clear that the spatial distribution of simulated precipitation can exert an important control on the strength of the overall response, particularly in models where the precipitation patterns are markedly asymetric.