Reserves of groundwater in much of the populated parts of Africa are being replenished at rates that could help to protect communities against the damaging effects of climate change and sustain widespread groundwater pumping for drinking water, a new study reveals.
Researchers estimate that the long-term groundwater recharge in Africa is approximately 15,000 km3 (cubic km) per decade and that recharge can occur even in arid and semi-arid areas.
This is equivalent to more than half the annual rainfall in Africa, which is replenishing the groundwater every decade.
Rapid population growth in many African countries and the effect of climate change on surface water has focused more attention on using groundwater as a reliable source of drinking water and irrigation.
In 2012, scientists at the British Geological Survey (BGS) led research which found that despite being a notoriously dry continent, Africa is actually sitting on a vast reservoir of groundwater.
But in many parts of the world, rapid increases in groundwater pumping have led to unsustainable conditions, often resulting in falling water tables and problems with water quality or subsidence.
Effective water supply investments can only be informed by reliable data, not only about where groundwater exists and how much can be stored, but also the rate at which groundwater is replenished, something which scientists refer to as ‘recharge’.
Now an international team of researchers led by the British Geological Survey (BGS) has published, for the first time, maps quantifying long-term average groundwater recharge in Africa using ground-based measurements.
The scientists mapped average groundwater recharge rates for the whole of Africa from 1970 to 2019, comparing results from over 134 separate studies and then combining it with data about available groundwater storage.
Writing in the journal, Environmental Research Letters, they say the maps provide a new and unique perspective of water security for Africa.
They argue that groundwater recharge must be assessed over decades, not individual years, because of the variability in the intensity of rainfall from year to year.
BGS Hydrogeologist, Prof Alan MacDonald, is lead author of the paper based at The Lyell Centre in Edinburgh and has led multiple studies on groundwater in Africa over the last two decades.
He said: “The data reveal some interesting patterns about Africa’s water security. We already know that having both low groundwater storage and recharge considerably reduces water security for local populations.
“What these new maps tell us is that the majority of African countries have either high storage, or high groundwater recharge.
“This is important because it provides essential insight into how Africa benefits from the distribution of groundwater storage and recharge.
“It shows where there is potential to sustainability develop more groundwater and also highlights where efforts should be targeted to carefully monitor groundwater supplies vulnerable to drought.”
The study shows that only five countries have both recharge and storage below the African average including eSwatini, Zambia, Lesotho, Zimbabwe and Eritrea, and extra care is needed to develop groundwater in these countries.
The maps show that many North African countries with little rainfall such as Libya, Algeria and Egypt, which are usually considered as water insecure, have considerable groundwater storage but very low recharge rates.
Prof MacDonald explains: “In these areas, we can see the groundwater is not connected to current climate and that groundwater pumping slowly depletes a finite reserve. Therefore increased groundwater pumping in the short term could ultimately be at the expense of future generations.
“Conversely, most African countries with little groundwater storage, such as Liberia, Cote D’Ivoire and Burundi, have regular recharge.
“In these areas, the little groundwater that exists is regularly topped up and so we know this can form a reliable supply. However if groundwater pumping is overused, for example for large scale irrigation, the groundwater could be in danger of drying up during droughts.”
The international study brings together international expertise form the UK, Africa and the US. Researchers hope that the maps will provide a valuable benchmark for assessing future models and a reliable baseline for future research.
Prof Seifu Kebede from the University of KwaZulu Natal, a co-author of the paper adds: “This effort brought together extensive African knowledge with expertise from other countries to provide information to sustainably develop water resources and overcome some of the most pressing issues countries often face, such as drought, deprivation, and starvation.”
The maps will be added to the online groundwater Atlas, which provides a publically available gateway for groundwater information in African countries.
The research was funded by the UPGro research programme, co-funded by the Natural Environment Research Council, UK Foreign, Commonwealth & Development Office and the Economic and Social Research Council.
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Notes to Editor:
British Geological Survey
The British Geological Survey (BGS) is a world leading applied geoscience research centre that is part of UK Research and Innovation (UKRI) and affiliated to the Natural Environment Research Council (NERC). BGS core science provides objective and authoritative geoscientific data, information and knowledge to inform UK Government on the opportunities and challenges of the subsurface. It undertakes national and public good research to understand earth and environmental processes in the UK and globally. The BGS annual budget of approximately £60 million p.a. is funded directly by UKRI, as well as research grants, government commissions and private sector contracts. Its 650 staff work across the UK with two main sites, the head office in Nottingham and Lyell Centre, a joint collaboration with Heriot Watt University in Edinburgh. BGS works with more than 150 private sector organisations, has close links to 40 universities and sponsors about 100 PhD students each year. See www.bgs.ac.uk.