Challenges of groundwater pollution and management in transboundary basins at the African scale

Abstract. We address the significant knowledge gap for groundwater pollution in Africa methods by assessing groundwater pollution risk at the African scale. To do so, we compiled the most recent continental-scale information on soil, land use, geology, hydrogeology, and topography in a Geographical Information System at the resolution of 15 × 15 km and the 1:60 000 000 scale. We produced a vulnerability map by using the generic DRASTIC vulnerability indicator. This map revealed that groundwater is highly vulnerable in Central and West Africa groundwater basins, where the water table is shallow. In addition, very low vulnerability classes are found in the large sedimentary basins of Africa deserts where groundwater is situated in very deep aquifers. The generic groundwater pollution risk map is obtained by overlaying the DRASTIC vulnerability indicator with current land use. The northern, central, and western parts of the African continent are dominated by high vulnerability classes and very strongly related to water table depths and the development of agricultural activities. Given the availability of data, we concentrate first on nitrate vulnerability mapping. To this end, groundwater nitrate contamination data are compiled in literature using meta-analysis technic and used to calibrate as well linear and nonlinear statistical models; the latter performing much better as compared to simple linear statistical models. This study will help to raise awareness of the manager's International Basin Authorities or Transboundary Basin Organizations in Africa and in particular on transboundary groundwater pollution issues.