The water balance of northern Africa during the mid-Holocene: An evaluation of the 6 Ka BP PMIP simulations

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 orbital forcing, sea surface temperatures, and CO2 concentration have been analyzed using a hydrological routing scheme (HYDRA) to simulate changes in lake area. The AGCM-simulated runoff produced six-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. The inter-model differences in simulated lake area are largely due to differences in simulated runoff (the squared correlation coefficient, R2, is 0.84). Most of these differences 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, the spatial distribution of simulated precipitation can exert an important control on the overall response.