The East African monsoons and their effects on agriculture

Abstract

Though the East African monsoons may be considered as mere extensions of the South Asian monsoonal system, they possess a number of characteristics which make them unique amongst the world's monsoons. The most important of these is the relative dryness of both the North and the South monsoon, caused by a prevalent low-level divergence over eastern Africa. Most rainfall in the region therefore occurs during the intermediate seasons between the monsoons, when this divergence is temporarily replaced by more convergent flow patterns. As a result, total rainfall in East Africa is relatively low. Over most of the region it is strongly concentrated during two short seasons and it is highly variable from year to year, both in total amount and in time of occurrence.

As in most parts of the tropics, rainfall is the main limiting factor in agricultural production in East Africa. The relations between rainfall and agriculture can be illustrated by the usual water balances, but an alternative method, employing the Agricultural Rainfall Indicator, is more useful for planning purposes. Drought frequencies, based on a simple relation between actual and average rainfall, also represent the effects of the monsoons on East African agriculture very clearly.