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Discussion papers | Copyright
https://doi.org/10.5194/hess-2018-516
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Oct 2018

Research article | 08 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

The El Niño event of 2015–16: Climate anomalies and their impact on groundwater resources in East and Southern Africa

Seshagiri Rao Kolusu1, Mohammad Shamsudduha2,3, Martin C. Todd1, Richard G. Taylor3, David Seddon3, Japhet J. Kashaigili4, Girma Y. Ebrahim5, Mark O. Cuthbert3,6, James P. R. Sorensen7, Karen G. Villholth5, Alan M. MacDonald8, and Dave A. MacLeod9 Seshagiri Rao Kolusu et al.
  • 1Department of Geography, University of Sussex, Brighton, BN1 9QS, UK
  • 2Institute for Risk and Disaster Reduction, University College London, Gower Street, London WC1E 6BT, UK
  • 3Department of Geography, University College London, Gower Street, London WC1E 6BT UK
  • 4Sokoine University of Agriculture, Morogoro, Tanzania
  • 5International Water Management Institute, Pretoria, South Africa
  • 6School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK
  • 7British Geological Survey, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB UK
  • 8British Geological Survey, The Lyell Centre, Research Avenue South, Edinburgh EH14 4AP UK
  • 9Oxford University, Atmospheric, Oceanic and Planetary Physics, UK

Abstract. The impact of climate variability on groundwater storage has received limited attention despite widespread dependence on groundwater as a resource for drinking water, agriculture and industry. Here, we assess the climate anomalies that occurred over Southern Africa (SA) and East Africa, south of the equator (EASE), during the major El Niño event of 2015–16, and their associated impacts on groundwater storage, across scales, through analysis of in situ groundwater piezometry and GRACE satellite data. At the continental scale, the El Niño of 2015–16 was associated with a pronounced dipole of opposing rainfall anomalies over EASE and Southern Africa, north/south of ~12°S, a characteristic pattern of ENSO. Over Southern Africa the most intense drought event in the historical record occurred, based on an analysis of the cross-scale areal intensity of surface water balance anomalies (as represented by the Standardised Precipitation-Evapotranspiration Index, SPEI), with an estimated return period of at least 200 years and a best estimate of 260 years. Climate risks are changing and we estimate that anthropogenic warming only (ignoring changes to other climate variables e.g. precipitation) has approximately doubled the risk of such an extreme SPEI drought event. These surface water balance deficits suppressed groundwater recharge, leading to a substantial groundwater storage decline indicated by both GRACE satellite and piezometric data in the Limpopo basin. Conversely, over EASE during the 2015–16 El Niño event, anomalously wet conditions were observed with an estimated return period of ~10 years, likely moderated by the absence of a strongly positive Indian Ocean Zonal Mode phase. The strong but not extreme rainy season increased groundwater storage as shown by satellite GRACE data and rising groundwater levels observed at a site in central Tanzania. We note substantial uncertainties in separating groundwater from total water storage in GRACE data and show that consistency between GRACE and piezometric estimates of groundwater storage is apparent when spatial averaging scales are comparable. These results have implications for sustainable and climate-resilient groundwater resource management, including the potential for adaptive strategies, such as managed aquifer recharge during episodic recharge events.

Seshagiri Rao Kolusu et al.
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