Modelling the impact of land surface degradation on the climate of tropical North Africa

The possibility that land surface degradation has contributed to persistently low rainfall in the Sahel is investigated with two GCMs. The COLA GCM is used to investigate the response to degradation of five different areas of tropical North Africa. The impact on rainfall varies considerably between the areas: degradation in the western Sahel results in a large reduction of rainfall, while degradation further east has less impact. Removal of coastal rain forest has little impact on rainfall as a result of a compensatory increase of moisture convergence. The Hadley Centre GCM confirms that degradation in the Sahel produces a large response. In all cases degradation reduces land surface evaporation and increases surface temperature but the response of the atmospheric moisture flux convergence differs between areas. Overall these results indicate that land surface processes can have a substantial effect on the climate of tropical Africa, particularly in the Sahel.