Seasonal Trends of Rainfall and Surface Temperature over Southern Africa

Abstract

This study investigated seasonal trends of surface temperature and rainfall from 1979 to 2007 in southern Africa. In recent years, annual rainfall has decreased over the African continent from the equator to 20ºS, as well as in Madagascar. On the other hand, annual mean surface temperature has shown an increasing trend across the whole region, with particularly large rates of increase in Namibia and Angola. The spatial and temporal structures of trends in rainfall and surface temperature have apparent seasonality, with rainfall in Angola, Zambia, and Namibia tending to decrease from December to March, and surface temperature from Namibia to southeastern South Africa tending to increase from July to October. To clarify the relationship between the seasonal trend and the interannual variation of the seasonal march of rainfall, empirical orthogonal function (EOF) analysis was applied to pentad rainfall data. The first and second modes of temporal structures showed strong seasonality, and their seasonal marches modulated after 1987 and 1995, respectively. These modulations included delay in rainy season onset, early withdrawal of the rainy season, and weak rainfall.