Southern African climate anomalies, summer rainfall and the Angola low
Anomalous climatic conditions have contributed to poverty, wlnerability and unemployment, which are major concerns of many southern African governments. Western countries continue to give food aid during drought periods and are looking for new and effective ways of supporting national food security plans (Walker, 1989a). Food security is a very difficult problem in Africa. A number of agricultural national programs have been planned to alleviate the problem but crop yields and living standards continue to deteriorate in many African countries. Unfavorable macro-economic conditions, debt repayments, civil war, political instabilities and mismanagement of resources make the situation more complex. It may be considered that anomalous climatic events (droughts or floods) are important factors, which contribute to acute food shortage. Seasonal rainfall forecasts are an important management tool for donor countries as well as local farmers. The failure to utilize forecasts based on sound scientific knowledge would negate attempts at achieving food security (W orId Meteorological Organization, 1996). It is for this reason that rainfall is an important input parameter in attaining self-sufficiency in food. Rainfall varies in space and time over southern Africa (preston-Whyte and Tyson, 1988; Walker 1989b; Mason, 1992; Rocha, 1992; Makarau, 1995). Further investigations of year-to-year variability of southern African summer rainfall are required in order to understand mechanisms and make accurate seasonal forecasts. Therefore, research work in climate should have high priority in African countries. The need to understand and predict the interannual variations of the atmosphere and the oceans has resulted in formation of global programs like the Tropical Ocean Global Atmosphere (TOGA) and World Climate Research Program (Climate Variability and Predictability, CLIVAR, 1995 and 1998). 2 Determination of the dynamics of droughts and floods continues to be a major problem. Correct prediction of extreme events such as droughts, floods, cold and warm spells involves knowing the mechanisms as well as the local and remote forcings. Several mechanisms have been suggested but more empirical research is required to understand and predict climate variability of southern African on intra-seasonal and inter-annual time scales. This study focuses on inter-annual and intra-seasonal variability of southern African climate with the view of identifying climatic regional and local features that influence summer rainfall and its fluctuations over southern Africa as whole. In order to achieve this, determination and refining of rainfall-SST anomaly relationships is carried out. Teleconnection patterns and coherent structure of interannual variability are revealed. Atmospheric mean meteorological features over Southern Africa and adjacent oceans have direct impact on summer rainfall. Thus determination of mean features using up-graded new and longer data sets provides a basis for investigating inter-annual and intraseasonal variability. This study presents mean characteristics of peak summer (December, January and February) based on 14 years ECMWF gridded data set. This study is motivated by a desire to understand climatic controls of interannual summer rainfall variability over southern African. The intensity of summer rainfall is modulated on synoptic, intra-seasonal, interannual and decadal time scales.
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