Trend of rainfall in East Africa

Abstract

Trends of rainfall in East Africa during the period 1922-1975 are examined using two independent approaches. namely the graphical and statistical methods. Under the graphical method the original and smoothed rainfall series were displayed visually on a graph. while the Spearman rank correlation test and the analysis of variance approach were employed in the statistical approach. The data used included the monthly. seasonal and annual rainfall records of about 100 stations during the period 1922-1975. The results of the study indicate significant trends of annual rainfall at nine stations when the Spearman rank correlation test was used. The smoothed graphs indicated similar tendencies at these stations during the period of study. The use of analysis of variance technique. however. indicated no significant difference between long-term averages and the averages of some standard periods at six of the nine stations. The only three stations where significant rainfall trends were indicated with both methods were Lodwar, Wajir and Magadi. All methods indicated an increasing annual rainfall tendency at these stations during the period of study. The results from the monthly. seasonal and regional rainfall records revealed no significant trends on the regionally averaged annual rainfall records. or on the monthly and dry season records. The wet seasons had characteristics close to those of the annual series.