2. Large Fluctuations in Rainfall
Generally, in Africa it is hard to define exactly what an “arid zone” is. However, areas that have an annual rainfall of less than 500 to 600 mm are usually considered unsuitable for farming. The figures below show the historical record of annual rainfall in the capital of Turkana District, located in the northwest of Kenya. As you can see, there is a lack of consistency in the amount of rain, as well as months that receive rainfall; the figures vary drastically depending on the year. Looking at the average rainfall of 45 years, from 1952–1997 (upper left), we see a general tendency for a large rainfall focused in April and a smaller rainfall in November. Yet, the variation is so large that the 45-year average does not offer us any specific annual rainfall pattern for estimation. In other words, one of the distinctive features of African arid zones is unpredictability regarding when it will rain. That is why people keep high mobility, as the situation demands, taking with them their domestic animals.