Semi-arid Regions and Rainfall 

The only thing common to all the semi-arid regions is low rainfall. Everything else varies so much that it is not practical to search for universal solutions. They may have temperate or tropical climates, rain in summer or winter, and different forms of agriculture.

Even when the climate is similar, other significant differences call for innovative technologies tailored to regions in West Africa. The main primary features of the environment in semi-arid Africa: a short rainy season, intensive rainfall interspersed with unpredictable droughts, and highly variable rainfall during the wet season. However, the duration of the rainy season is longer, and the curve of potential evapotranspiration is bimodal (dry & rainy seasons) in West Africa.

The two key features which adversely affect agriculture are the low amounts of rainfall and unreliability. These linked problems in that the variability becomes more significant as the mean rain decreases. The low quantities of rain lead to several constraints. Cropping may not be possible at all or likely only with special techniques such as fallows or furrows to collect more rain. The range of suitable species will be limited, and in the semi-arid tropics with summer rainfall, it is usual to grow maize where the rainfall permits, then sorghum where the rain is not sufficient for maize, and millet where the rain is not enough for sorghum. Farmers must strategize and direct towards minimizing the loss or wastage of rainfall.