Rainfall variability and changes in southern Africa during the 20th century in the Global warming context

摘要

Rainfall variability and changes in Southern Africa over the 20th century are examined and their potential links to the global warming discussed. After a short review of the main conclusions of various experiments with Global Atmospheric Models (GCM) forced by increased concentrations of greenhouse gases for Southern Africa, a study of various datasets documents the observed changes in rainfall features at both daily and seasonal time steps through the last century. Investigations of daily rainfallparameters are so far limited to South Africa. They show that some regions have experienced a shift toward more extreme rainfall events in recenl decades. Investigations of cumulative rainfall anomalies over the summer season do not show any trend to drier or moister conditions during the century. However, close examination reveals that rainfall variability in Southern Africa has experienced significant modifications, especially in the recenl decades. Interannual variability has increased since the late1960s. In particular, droughts became more intense and widespread. More significantly, teleconnection patterns associated with Southern African rainfall variability changed from regional before the 70s to near global after, and an increased statisticalassociation to the El Nino - Southern Oscillation (ENSO) phenomenon is observed. Numerical experiments with a French GCM indicate that these changes in teleconnections could be related to long-term variations in the Sea-Surface-Temperature background, which are par! of the observed global warming signal.