Rainfall Variability in Africa

Abstract

Time series of annual rainfall for 69 stations in Africa were analyzed for trends and periodicities. Trend analysis showed that most of the annual series indicate some forms of oscillations rather than any particular trend. Use of binomial coefficients to smooth the series indicated positive or negative trends in recent years in 20 series, but only four of these were statistically significant judging by the Spearman rank correlation test. These four stations were geographically distributed within those showing no significant trends. Assuming the generating process to be purely random, the prominent cycles revealed by the spectral analysis were 2.0?2.5 years and 2.7?3.3 years. In general, the larger observed cycles (3.5?4.4 years, 5.0 years, 6.0?6.5 years, 7.0?8.0 years and 10.0 years) were weak at the 0.05 significance level.