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African groundwater offers hope for climate variability 'buffer'

Last modified April 30, 2012 08:49

Groundwater is the major source of drinking water in Africa and is likely to be used increasingly for irrigation of food crops. But little is known about how much there actually is, and so assessments of freshwater availability do not include groundwater storage. Now a team from the UK has estimated Africa's groundwater resources for the first time.

According to Alan MacDonald of the British Geological Survey, Africa's groundwater resources are estimated to be more than 100 times the annual renewable freshwater resources and 20 times more than is stored in Africa's freshwater lakes. "We also show that this groundwater will not be available for widespread development of high-yielding boreholes (for example for irrigation), but is likely to support low-yielding boreholes for drinking water supply and small community scale irrigation," he told environmentalresearchweb.

More than 300 million people in Africa do not have access to safe drinking water, and only 5% of arable land is irrigated.

To obtain the result, MacDonald and colleagues reviewed available maps, publications and data to create the first quantitative continent-wide maps of aquifer storage and potential borehole yields. The team estimated the total groundwater storage in Africa at 0.66 million km3, with a range of 0.36 to 1.7 million km3.

"There has been very little information on the volume of groundwater available and how it will respond to climate change – consequently it is very rarely taken into account when discussing water scarcity," said MacDonald. "We thought it was about time to start gathering quantitative information so people have some evidence on which to make decisions on groundwater development."

The groundwater resources are unevenly distributed, with the biggest volumes in the large sedimentary aquifers in the northern states of Algeria, Egypt, Libya and Sudan. But the researchers say that in many countries, appropriately sited and constructed boreholes can support handpump abstraction, and contain sufficient storage to sustain abstraction through inter-annual variations in recharge. But the potential for boreholes yielding more than 5 litres of water per second was much more limited.

"The large groundwater storage offers an excellent buffer to increased climate variability brought on by climate change," said MacDonald. "Given the variability in permeability of the rocks, large commercial irrigation projects requiring high-yielding boreholes should not be developed without a thorough understanding of the local groundwater conditions. Appropriately sited and developed boreholes for low-yielding rural water supply and handpumps are likely to be successful and resilient to climate change."

Groundwater could provide a buffer against climate variability as it responds much more slowly to meteorological conditions than surface water.

"In Africa we are now using satellite information to work out whether groundwater levels are falling or rising," said MacDonald. "We have been asked to carry out a similar type of project in South-East Asia looking at how groundwater responds in the Indus Ganges Basin."

MacDonald and colleagues reported their work in Environmental Research Letters (ERL).

About the author

Liz Kalaugher is editor of environmentalresearchweb.

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