ORIGINAL: Environmental Research Letters
In Africa, groundwater is the major source of drinking water and its use for irrigation is forecast to increase substantially to combat growing food insecurity. Despite this, there is little quantitative information on groundwater resources in Africa, and groundwater storage is consequently omitted from assessments of freshwater availability. Here we present the first quantitative continent-wide maps of aquifer storage and potential borehole yields in Africa based on an extensive review of available maps, publications and data. We estimate total groundwater storage in Africa to be 0.66 million km3 (0.36–1.75 million km3). Not all of this groundwater storage is available for abstraction, but the estimated volume is more than 100 times estimates of annual renewable freshwater resources on Africa. Groundwater resources are unevenly distributed: the largest groundwater volumes are found in the large sedimentary aquifers in the North African countries Libya, Algeria, Egypt and Sudan. Nevertheless, for many African countries appropriately sited and constructed boreholes can support handpump abstraction (yields of 0.1–0.3 l s-1), and contain sufficient storage to sustain abstraction through inter-annual variations in recharge. The maps show further that the potential for higher yielding boreholes ( > 5 l s-1) is much more limited. Therefore, strategies for increasing irrigation or supplying water to rapidly urbanizing cities that are predicated on the widespread drilling of high yielding boreholes are likely to be unsuccessful. As groundwater is the largest and most widely distributed store of freshwater in Africa, the quantitative maps are intended to lead to more realistic assessments of water security and water stress, and to promote a more quantitative approach to mapping of groundwater resources at national and regional level.
The production of the first quantitative maps of groundwater resources in Africa reveals the magnitude and distribution of freshwater stored as groundwater. The volume of groundwater is estimated to be 0.66 million km3, more than 100 times the annual renewable freshwater resources, and 20 times the freshwater stored in African lakes. As the largest and most widely distributed store of freshwater in Africa, groundwater provides an important buffer to climate variability and change. The maps presented here are designed to give a continent-wide view of groundwater and to encourage the development of more quantitative national and sub-national quantitative maps and assessments to support the development of groundwater-based adaptation strategies to current and future climate variability. In addition, the maps enable the explicit representation of groundwater storage in assessments of water scarcity and strategies to achieve water security.
The maps demonstrate the uneven distribution of groundwater across the continent and in particular the large groundwater volumes available in the sedimentary basins of north Africa. The potential for boreholes yielding greater than 5 l s-1 outside of large sedimentary basins is not widespread but limited to particular areas requiring careful exploration and development. Nevertheless, for many African countries appropriately sited and constructed boreholes will support a handpump (a yield of 0.1–0.3 l s-1), and sufficient storage is available to sustain abstraction through inter-annual variations in recharge.
