Variability analysis of river flows in the region of Southern Africa.

Spatial and temporal variability of river flow is investigated in 502 river flow gauging stations in nine countries of the Southern African region with a view to document the spatial variability and to identify those regions where there is strong evidence of declining or increasing trend in annual runoff. The data used is of monthly and annual duration. The study has shown that runoff in the region ranges from over 320 mm/year in the highlands of southern Tanzania and North eastern South Africa to less than 10 mm/year in the dessert areas of Namibia and the Kalahari. There is evidence of declining runoff in parts of Zambia, Angola, Mozambique and the Veld in South Africa. The main starting time of decreasing annual runoff yields in these areas is between 1977 - 1984. A trend of increasing flows with weak spatial variation and poor clustering is significant in a few of the basins in the region during the same time. Cases in point are the basins clustered around the Southwest Lake shore river basin in Malawi. Attempts to investigate whether the findings are due to local causes or a more general climatic forcing by analyzing annual rainfall records from 800 stations in eight of the countries in the study area have proved to be inconclusive. However, the results show that significant regional variability has occurred in the river flow regimes of the southern Africa region over the last fifty years.