Review: Groundwater recharge estimation in arid and semi-arid southern Africa

Groundwater recharge estimation in arid and semi-arid southern Africa is reviewed based on four decades of recharge investigation in the region. This paper updates an earlier review by incorporating emerging and grey literature from a wide range of research sectors in southern Africa, collected during the past decade. For ease of comparison, methods commonly used are critically reviewed with a rating provided in terms of accuracy, application and costs. These include, but are not limited to, the methods of chloride mass balance (CMB), rainfall infiltration breakthrough (RIB), Extended model for Aquifer Recharge and moisture Transport through unsaturated Hardrock (EARTH), water-table fluctuation (WTF), water balance in the saturated zone (including equal volume spring flow (EVSF) and saturated volume fluctuation (SVF)), and groundwater modelling (GM). As the methods based on mass balance and relationships between rainfall, water-level fluctuations and abstraction are proven to have the potential to simulate and forecast groundwater recharge, the EVSF and CMB methods are highly recommended for use in the southern African region according to this review. Caution on the uncertainty associated with error input and propagation for all the methods is advised, based on a case study in South Africa. The review provides an updated source of references related to recharge estimation in arid and semi-arid regions of Sub-Saharan Africa in general and to ongoing projects for the implementation for Resource Directed Measures (part of the National Water Resources Strategy) in South Africa in particular.