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Evidence of the dependence of groundwater resources on extreme rainfall in East Africa

Abstract

Groundwater recharge sustains the groundwater resources on which there is global dependence for drinking water and irrigated agriculture1. For many communities, groundwater is the only perennial source of water. Here, we present a newly compiled 55-year record of groundwater-level observations in an aquifer of central Tanzania that reveals the highly episodic occurrence of recharge resulting from anomalously intense seasonal rainfall. Episodic recharge interrupts multiannual recessions in groundwater levels, maintaining the water security of the groundwater-dependent communities in this region. This long-term record of groundwater storage changes in the semi-arid tropics demonstrates a nonlinear relationship between rainfall and recharge wherein intense seasonal rainfall associated with the El Niño Southern Oscillation and the Indian Ocean Dipole mode of climate variability2,3 contributes disproportionately to recharge. Analysis of the Intergovernmental Panel on Climate Change AR4 and AR5 multi-model ensembles for the twenty-first century indicates that projected increases in extreme monthly rainfall, responsible for observed recharge, are of much greater magnitude than changes to mean rainfall. Increased use of groundwater may therefore prove a potentially viable adaptation to enhanced variability in surface-water resources and soil moisture resulting from climate change4,5,6,7. Uncertainty in the projected behaviour of the El Niño Southern Oscillation and associated teleconnections remains, however, high8.

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Figure 1: 55-year observational record of groundwater levels, rainfall and groundwater abstraction from central Tanzania.
Figure 2: Analysis of the relationship between groundwater recharge and rainfall.
Figure 3: Analysis of climate variability associated with major groundwater recharge events.
Figure 4: Projected changes in mean and extreme monthly rainfall in central Tanzania.

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Acknowledgements

The study was supported by a grant (Ref. GA/09F/094) from the UK Department for International Development (DFID), Groundwater resilience to climate change in Africa. The authors are grateful to the climate modelling groups and the CMIP projects for making model data available and to the Dodoma Urban Water Supply and Sewerage Authority for access to water supply records. The views expressed in this paper are those of the authors alone.

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Contributions

The Makutapora record was compiled by L.K., E.N., R.G.T., L.M. and H.S. Recharge analyses were conducted by R.G.T., M.C.T., A.M.M. and L.M. M.C.T. performed the analysis of climate data and model projections. R.G.T., M.C.T. and L.M. conceived the paper and R.G.T. and M.C.T. wrote the paper with feedback from all other authors.

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Correspondence to Richard G. Taylor.

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The authors declare no competing financial interests.

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Taylor, R., Todd, M., Kongola, L. et al. Evidence of the dependence of groundwater resources on extreme rainfall in East Africa. Nature Clim Change 3, 374–378 (2013). https://doi.org/10.1038/nclimate1731

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