Do land use induced changes of evaporation affect rainfall in Southeastern Africa?

Abstract

In Southeastern Africa the major part of the rainfall returns to the air by evaporation before it reaches the Indian Ocean. Except for slope and soil, land use is of influence on evaporation. During rainfall events a portion of the precipitable water in the atmosphere reaches the ground. Without a stronger cooling mechanism than the previous one (for instance a major orographic effect), the atmosphere can only generate rainfall downwind if the precipitable moisture is again replenished by evaporation. Since the actual evaporation on average is less than the rainfall, the rainfall downwind decreases. Land degradation decreases the replenishment and hence the rainfall downwind. Southeastern Africa suffered from severe droughts in the past decennia. In the same period large scale land use change took place. The area covering Zimbabwe, Zambia and Mozambique is being studied. A simple advection dispersion equation is used to model the atmosphere. A similar model gave promising results in the Sahel region. If the method proves applicable, than estimates can be given about the consequences of land use changes in certain regions on rainfall elsewhere.