Daily rainfall variability in Southern Africa.

Qwabe, Sabatha Thulane
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Clear characterisation of daily rainfall over the southern African continent is necessary for the purpose of achieving sustainable human and agricultural-environmental development. In this research, daily rainfall variability over southern Africa is investigated to determine the relations between rainfall, rainfall frequency, and amount of rain per rain day. Firstly, the characterisation of daily rainfall over the region from 1950 to 1997 is given. This is followed by the analysis of daily rainfall variability during the 10 wettest and driest years. Thirdly, the influence of Sep-Nov and Dec-Feb seasons on the 10 wettest and driest years is then highlighted. Lastly, to determine whether the relation between the three rainfall parameters determined over the whole southern African region holds true for local areas, daily rainfall variability over Swaziland during the period of meteorological records is discussed. Analyses of daily rainfall over southern Africa indicate that on scales of days to years, rainfall departures from mean result from changes in both daily rainfall frequency and intensity. Positive rainfall changes are due to an increase in the number of rainy days and amount of rainfall falling on those rain days. Negative rainfall changes results from a decrease in rainfall frequency and rain falling on those rain days. Southern Africa does not show uniform changes in these rainfall variables, but patterns. of spatial and temporal variability. This variability increases from the Western regions of the subcontinent (i.e. rainfall variability increases from the eastern humid to the western arid regions of the subcontinent). The conclusion is that over the whole of southern African region changes in mean rainfall are dependent on the number of rain days and rain per rain day. This result also holds true over smaller areas of the subcontinent, such as Swaziland.