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Summary
Eighteen series of annual rainfall totals over the non-irrigated area of the sugar region of South Africa were submitted to principal components analysis. Three components accounted for 84 per cent of the total rainfall variance. These components may be identified with the general behaviour of rainfall from year to year, a compensatory system between the northern and southern areas of the sugar region, and a minor compensatory system within the southern part of the region respectively. The first component, from a spectral analysis, exhibited three major wave patterns, namely, wave lengths of 19, 6,8 and 2.2 years. The application of band pass filters to the longest record showed that the 19-year wave has been stable over three complete cycles, the 2,2-year wave has run true over the period of record but has suffered three extreme amplitudes, while the 6,8-year wave appears not to be stable over time or amplitude. With reservations, the first two waves may have forecasting potential, but the latter one does not.