Residence times of shallow groundwater in West Africa: implications for hydrogeology and resilience to future changes in climate

• Published in: Hydrogeology journal Vol. 21; no. 3; pp. 673 - 686
• Main Authors: Lapworth, D. J., MacDonald, A. M., Tijani, M. N., Darling, W. G., Gooddy, D. C., Bonsor, H. C., Araguás-Araguás, L. J.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.05.2013; Springer Nature B.V
• Subjects: Annual rainfall; Aquatic Pollution; Aquifers; Basements; Climate; Earth and Environmental Science; Earth Sciences; Geology; Geophysics/Geodesy; Groundwater; Hydrogeology; Hydrology/Water Resources; Rainfall; Resilience; Rural; Waste Water Technology; Water Management; Water Pollution Control; Water Quality/Water Pollution; Africa; Environmental tracers; Groundwater recharge; Climate variability; Groundwater age; Africa
• ISSN: 1431-2174; 1435-0157
• DOI: 10.1007/s10040-012-0925-4

Although shallow groundwater (<50 mbgl) sustains the vast majority of improved drinking-water supplies in rural Africa, there is little information on how resilient this resource may be to future changes in climate. This study presents results of a groundwater survey using stable isotopes, CFCs, SF 6 , and 3 H across different climatic zones (annual rainfall 400–2,000 mm/year) in West Africa. The purpose was to quantify the residence times of shallow groundwaters in sedimentary and basement aquifers, and investigate the relationship between groundwater resources and climate. Stable-isotope results indicate that most shallow groundwaters are recharged rapidly following rainfall, showing little evidence of evaporation prior to recharge. Chloride mass-balance results indicate that within the arid areas (<400 mm annual rainfall) there is recharge of up to 20 mm/year. Age tracers show that most groundwaters have mean residence times (MRTs) of 32–65 years, with comparable MRTs in the different climate zones. Similar MRTs measured in both the sedimentary and basement aquifers suggest similar hydraulic diffusivity and significant groundwater storage within the shallow basement. This suggests there is considerable resilience to short-term inter-annual variation in rainfall and recharge, and rural groundwater resources are likely to sustain diffuse, low volume abstraction.