Groundwater – a vital source of water for drinking and irrigation across sub-Saharan Africa – is, to a certain extent, resilient to climate variability and change, according to a new study co-led by IRD with University College London and Cardiff University. The research published on August 7, 2019 in Nature shows how groundwater replenishment can depend upon heavy rainfalls and flood events, amplified by climate change.
Groundwater plays a central role in sustaining water supplies and livelihoods in sub-Saharan Africa due to its widespread availability, generally high quality, and intrinsic ability to buffer episodes of drought and increasing climate variability. In Benin for example, IRD alongside with the National Institute of Water (INE) showed that, in hard rocks covering about 80% of the country's surface area, the groundwater reserve is about 440 litres of water per square meter of surface area; this reserve could buffer variations in climate during more than 6 years on average (Vouillamoz et al., 2015). Professor Moussa Boukari, co-lead of this study in Benin, said: "Groundwater offers a potential pathway to sustain increases in freshwater use required to achieve UN Sustainable Development Goals 2 (zero hunger) and 6 (safe water for all)".
A long-term observation network
The study published in Nature was carried out by a consortium of 32 international scientists, including Benin's scientific partners of IRD, INE and the General Directorate for Water (DG-Eau). The research involved the collation of multi-decadal records of groundwater levels1 and rainfall to examine how the replenishment of groundwater has responded to variations in climate and geology. The team analysed observations compiled from nine countries across sub-Saharan Africa (Benin, Burkina Faso, Niger, Ghana, Tanzania, Uganda, Zimbabwe, Namibia, South Africa) representing a range of climates from hyper-arid to humid.
The study shows that in humid areas as in Benin, groundwater is replenished primarily by rainfall that directly infiltrates the land surface, whereas in drylands it occurs predominantly by leakage from temporary streams and ponds. Local geology also plays a role in determining the sensitivity of rates of replenishment to changes in climate. In Benin for example, a previous study carried out by IRD, INE and DG-Eau, indicates that the annual groundwater replenishment is about 8 times lower in hard rocks as compared to unconsolidated sand, with comparable amount and intensity of rainfall (Kotchoni et al., 2018).
This research also shows that, in drylands, the heavy rainfalls and flood events generating groundwater replenishment are commonly associated with climate variation phenomena such as El Niño and La Niña.
Promoting the adaptation of populations
Professor Richard Taylor (UCL), co-lead on the study, said: “Previous regional-level assessments of groundwater resources using large-scale models have ignored the contribution of leaking streams and ponds to groundwater supplies, underestimating its renewability in drylands and resilience to climate change."
“Knowledge of the replenishment process can inform strategies to enhance groundwater supplies. In drylands, where groundwater resources are often the only lasting source of freshwater, such strategies can further exploit the predictability of heavy rainfalls and flood events that generate groundwater,” added Jean-Michel Vouillamoz, IRD hydrogeologist who co-leads the works in Benin.
1. Recordings of groundwater level changes over periods of several decades are rare in Africa. In Benin, DG-Eau and INE have set up long-term observation networks. They are essential for understanding climate variations.
Contact: firstname.lastname@example.org, hydrogeologist and geophysicist at IRD (UMR IGE)
Reference: Cuthbert, M, Taylor, R, Favreau, G. et al. Observed controls on resilience of groundwater to climate variability in sub-Saharan Africa, Nature, August 7th 2019.