Recharge

Africa Groundwater Atlas >> Additional resources >> Recharge

Groundwater recharge is one of the most difficult parameters to measure in the assessment of groundwater resources, but it is critical for reliable projections of sustainable resource development.

There have been many studies of groundwater recharge across Africa. These vary significantly in terms of the study scale; the geographical, climatic and geological characteristics of the region of interest; the quality of data used; and the estimation methods applied.

Global Recharge Estimates

At a global scale, Döll and Fiedler (2008) provide estimates of long term average diffuse groundwater recharge based on the WaterGAP Global Hydrology Model. The model is run with a daily time-step at a spatial resolution of 0.5°, and is driven by gridded precipitation data. Model parameters are adjusted to match observed long-term average river discharge at more than 1000 gauging stations around the world.

Doll P & Fiedler K. 2008. Global-scale modelling of groundwater recharge. Hydrol. Earth Syst. Sci. 12, 863-885. doi:10.5194/hess-12-863-2008.

Overview of Recharge Studies in Africa

Bonsor and MacDonald (2010) reviewed around 100 recharge studies from across the continent and ranked each study according to a set of confidence criteria. They summarise the applicability of the following estimation techniques for different geographical settings applicable to Africa:

• Chloride mass balance
• Water balance methods
• Water table fluctuations
• Groundwater residence times
• Groundwater modelling

Bonsor HC & MacDonald AM. 2010. Groundwater and climate change in Africa: review of recharge studies. British Geological Survey Internal Report (IR/10/075)

UPGro

An UPGro catalyst project, finished in 2014, investigated groundwater recharge in Africa: identifying critical thresholds. The project carried out a review of more than 200 recharge studies in Africa, examining relationships between rainfall and recharge, and evidence for thresholds controlling recharge. Key findings from the project were:

the importance of using multiple methods to estimate recharge;

the importance of reporting recharge as decadal, rather than annual averages, because of the high year-to-year variability in recharge, particularly in semi-arid and arid regions;

while broad relationships exist between average rainfall and recharge, such relationships becomes non-linear when long-term average annual rainfall is less than 1000 mm. In such low rainfall areas, rainfall intensity becomes particularly important in controlling recharge. In future, climate change is expected to lead to increased rainfall intensity, and so a better understanding of the role of episodic high intensity rainfall events in governing recharge will become increasingly important.

Africa Groundwater Atlas >> Additional resources >> Recharge