Secular variation in South African rainfall

Abstract

Annual rainfall totals over South Africa during the period 1910 - 1972, and where availability of data permitted for the period 1880 - 197J, are examined for evidence of secular variation. It is shown that no evidence exists to support the view that the sub-continent is undergoing progressive desiccation. With the aid of a linear model station records, grouped using principal component ana? vsis, are shown in some cases to possess trend on a micro-scale. Strong evidence is provided to support the hypothesis that rainfall is oscillatory in nature. Oscillations in the ranges 16-20, 10-12, and 2 - 3 years are shown by different methods to be spatially dependent. A 3 - 4 year oscillation is ubiquitous. The plausibility of using stochastic models to forecast annual rainfall totals is investigated and tentative forecasts made regarding the general pattern of rainfall behaviour over some regions of South Africa.