Surface Albedo–Climate Feedback Simulated Using Two-Way Coupling

Abstract

To simulate the effects of feedback between climate and surface albedo via vegetation, a scheme was developed, based on a generalized life zone scheme, for estimating the land surface albedo as a function of annual mean precipitation and surface temperature. This scheme was applied to the climate of a GCM and made interactive with the GCM. The climate of this run was compared with one in which the land surface albedo was prescribed to a spatially uniform value. Allowing such feedback within the modeling system enhances the atmospheric ascent and heavy precipitation of tropical rainbelts, in comparison with a case with spatially homogeneous surface albedo prescribed. It also intensifies the atmospheric descent and low precipitation rates over subtropical latitudes. That is, a positive feedback occurs at low latitudes. At midlatitudes, thermal forcing due to the spatial distribution of surface albedo has little effect on vertical motion or precipitation. However, in the Central Asian and Gobi Deserts, the high surface albedo cools the surface, reduces evaporative demand, and allows the soil and vegetation to retain more moisture, indicating negative feedback. Because the northern edge of the Sahara has negative feedback similar to that in midlatitudes, while the southern part has positive feedback, the Sahara as a whole is shifted southward when surface albedo feedback is included.