Groundwater in sub-Saharan Africa supports livelihoods and poverty alleviation(1,2), maintains vital ecosystems, and strongly influences terrestrial water and energy budgets(3). Yet the hydrological processes that govern groundwater recharge and sustainability-and their sensitivity to climatic variability-are poorly constrained(4,5). Given the absence of firm observational constraints, it remains to be seen whether model-based projections of decreased water resources in dry parts of the region(4) are justified. Here we show, through analysis of multidecadal groundwater hydrographs across sub-Saharan Africa, that levels of aridity dictate the predominant recharge processes, whereas local hydrogeology influences the type and sensitivity of precipitation-recharge relationships. Recharge in some humid locations varies by as little as five per cent (by coefficient of variation) across a wide range of annual precipitation values. Other regions, by contrast, show roughly linear precipitation-recharge relationships, with precipitation thresholds (of roughly ten millimetres or less per day) governing the initiation of recharge. These thresholds tend to rise as aridity increases, and recharge in drylands is more episodic and increasingly dominated by focused recharge through losses from ephemeral overland flows. Extreme annual recharge is commonly associated with intense rainfall and flooding events, themselves often driven by large-scale climate controls. Intense precipitation, even during years of lower overall precipitation, produces some of the largest years of recharge in some dry subtropical locations. Our results therefore challenge the 'high certainty' consensus regarding decreasing water resources(4) in such regions of sub-Saharan Africa. The potential resilience of groundwater to climate variability in many areas that is revealed by these precipitation-recharge relationships is essential for informing reliable predictions of climate-change impacts and adaptation strategies.
1.UCL, Dept Geog, London, England 2.Cardiff Univ, Sch Earth & Ocean Sci, Cardiff, S Glam, Wales 3.Univ New South Wales, Connected Waters Initiat Res Ctr, Sydney, NSW, Australia 4.Cardiff Univ, Water Res Inst, Cardiff, S Glam, Wales 5.Inst Rech Dev, Niamey, Niger 6.Univ Sussex, Dept Geog, Falmer, England 7.UCL, Inst Risk & Disaster Reduct, London, England 8.Int Water Management Inst, Pretoria, South Africa 9.British Geol Survey, Lyell Ctr, Edinburgh, Midlothian, Scotland 10.Univ Texas Austin, Jackson Sch Geosci, Bur Econ Geol, Austin, TX 78712 USA 11.Inst Rech Dev, Cotonou, Benin 12.Inst Rech Dev, Grenoble, France 13.Direct Gen Eau, Cotonou, Benin 14.Sokoine Univ Agr, Dept Forest Resources Assessment & Management, Morogoro, Tanzania 15.British Geol Survey, Maclean Bldg, Wallingford, Oxon, England 16.Makerere Univ, Dept Geol & Petr Studies, Kampala, Uganda 17.Makerere Univ, Dept Civil & Environm Engn, Kampala, Uganda 18.Univ Abdou Moumouni, Dept Geol, Niamey, Niger 19.Univ Maiduguri, Dept Geol, Maiduguri, Nigeria 20.Cemex, Rugby, England 21.Water Res Inst, Accra, Ghana 22.Univ Ouaga Pr Joseph Ki Zerbo, Dept Sci Terre, Ouagadougou, Burkina Faso 23.Univ Namibia, Dept Geol, Windhoek, Namibia 24.Univ West England, Dept Geog & Environm Management, Bristol, Avon, England 25.Univ Tokyo, Inst Ind Sci, Tokyo, Japan 26.Int Inst Appl Syst Anal, Laxenburg, Austria 27.Natl Taiwan Univ, Dept Atmospher Sci, Taipei, Taiwan 28.Univ Tokyo, Inst Future Initiat, Tokyo, Japan 29.Int Groundwater Resources Assessment Ctr, Delft, Netherlands
Recommended Citation:
Cuthbert, Mark O.,Taylor, Richard G.,Favreau, Guillaume,et al. Observed controls on resilience of groundwater to climate variability in sub-Saharan Africa[J]. NATURE,2019-01-01,572(7768):230-+