Figure 7.9: Newly exposed water resources. It was long thought that Africa had only shallow and sparse deposits of groundwater. But recent research has revealed that for the African continent, the quantity of water stored in aquifers is nearly 100 times that of previous estimates. Some is near the surface and relatively accessible, but because much is fossil water deposited as many as 5000 years ago, it cannot be recharged (replenished) quickly under present drier climate conditions. Also, many densely populated areas have only small deposits. Compare this map of the depth of groundwater deposits and number of years needed to recharge with the Figure 7.22 population map.
[Sources consulted: A. M. MacDonald, H. C. Bonsor, B. E. O. Dochartaigh, and R. G. Taylor, 2012, “Quantitative Maps of Groundwater Resources in Africa,” Environmental Research Letters 7. doi:10.1088/1748- 5–