Rainfall Variability in Africa
Time series' of annual rainfall for 69 stations in Africa we~e analyzed for trends an? p~riodicities. Trend analysis showed that most of the annual series indicate some forr~s ~f ?sclllatlons .. rather than any particular trend. Use of binomial coefficients to smooth the senes m~lc~ted po.sltl.ve or negative trends in recent years in 20 series, but only four of these were. statlstl~al~y slgmfi.ca?t 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.