A literature review of recharge estimation and groundwater resource assessment in Africa

This report reviews the available literature on groundwater recharge and groundwater resource assessment in Africa. The purpose of this review is to identify estimates of groundwater recharge that have been undertaken either in Africa, or outside Africa but in similar environments and climates to those found in Africa. The first part of the report highlights the importance of groundwater recharge modelling to the study of climate change impacts on groundwater resources in Africa. Section 2 discusses groundwater recharge mechanisms, and challenges in recharge estimation, particularly in arid and semi-arid regions. Sections 3, 4, 5, and 6 largely describe groundwater recharge studies in arid and semi-arid areas, especially in Africa, which used different methods at different scales. In the final part of the report we emphasize our main conclusion: • There is a gap in information on the scale and temporal and spatial distribution of groundwater recharge across much of Africa. Most existing recharge estimates have been done on an ad hoc basis using very different methods and data, so that there is no consistency between estimates in different regions. The distribution of these estimates across Africa is also patchy and unequal. • There is potential value in producing a process-based quantitative continental scale recharge estimate that uses a consistent approach and data, as the basis for studying potential climate change impacts on groundwater resources in Africa. The only existing continental scale recharge model, the WaterGAP Global Hydrology Model (WGHM) (Döll et al. 2003, Döll and Flörke 2005, and Döll and Fiedler 2008), was originally designed to estimate global runoff, and does not fully quantitatively account for detailed hydrogeological processes, in particular for soil moisture change processes related to groundwater recharge. • Developing a continental-scale recharge model that accounts for the highly variable climate zones across Africa, with the limited available data, is a great challenge. Modelling recharge is particularly difficult in arid and semi-arid areas.