CLIMATIC VARIABILITY AND CHANGE OVER SOUTHERN AFRICA - A REFLECTION ON UNDERLYING PROCESSES

Quasi-periodicities in annual rainfall totals over southern Africa hav e been identified; in particular, an approximately 18-year cycle may b e related to interdecadal variability in sea-surface temperatures in t he eastern equatorial Pacific and central Indian Oceans. A 10-year cyc le along the south coast is related to variability in standing wave 3. Atmospheric anomalies associated with wet and dry years can be relate d to changes in the frequency, intensity and persistence of important rainfall-producing weather systems and highlight the significance of t he strength of the continental heat low and the preferred locations an d amplitudes of the westerly troughs. El Nino-Southern Oscillation eve nts and sea-surface temperature anomalies in the Indian and South Atla ntic Oceans can influence both the tropical and the temperate atmosphe ric circulation and moisture fluxes over the subcontinent and thus are significant influences on rainfall variability. Evidence for long-ter m climatic change is not as definitive as in the Sahel, although there are indications of desiccation in some areas since the late-1970s. In creases in temperatures are of approximately the same magnitude as the hemispheric trends and may be attributable to the enhanced greenhouse effect.