DROUGHTS OVER SOUTHERN AFRICA IN A DOUBLED-CO2 CLIMATE

The southern African region is susceptible to climatic extremes and pa rticularly to extended dry periods. Possible changes in the probabilit y of dry years under doubled-CO2 conditions are examined using output from the CSIRO nine-level general circulation model. Changes in annual mean rainfall are not expected to be significant. However, the model simulates an increase in the probability of dry years in the tropics, to the south-west of the subcontinent, as well as over the western and eastern parts of South Africa and southern Mozambique, where large pe rcentage increases in the most intense dry spells are indicated. A dec rease in the frequency of dry years is simulated over much of the inte rior of the subcontinent south of 10 degrees S. In regions where the f requency of dry years decreases, the most severe events occur less oft en. The CSIRO nine-level model indicates a shift in the frequency dist ribution of daily rainfall events under doubled-CO2 conditions. A smal l change in the frequency distribution of daily rainfall events may ha ve further implications for the frequency of mid-summer droughts durin g the peak summer rainfall period of December-February. Increases in t he frequency of mid-summer droughts are simulated over the eastern par t of the subcontinent south of 20 degrees S.