June July Aug Sept Oct Nov Dec
Case study 10.4 Effect of land use on the soil water balance in Sub-Saharan Africa. To complete this chapter, we consider a case study of the annual water balance of deep sandy soils at a site just south of Niamey (the capital of Niger, West Africa). The average annual rainfall is about 550mm and is compressed into a few months of rainy season (May-October). It is an area of the world where there is concern that the climate is changing so as to reduce the annual rainfall, because the rainfall in most years of the past decade or so has been below the previous longterm year average. It is also an area with a dramatically increasing population, resulting in increased abstraction of water from boreholes and wells (groundwater is the main source of water for villages). The demands of increased population pressure have also led to an increase in the clearance of natural savannah vegetation (bushes with a herbaceous understorey) in order to grow arable crops with minimal inputs of fertilizers. Given the changes in the past decade in rainfall, water abstraction and land use, it is not surprising that there has been a change in groundwater levels, though it is not clear the extent to which each cause has contributed to the change.