LONDON, April 20 (Reuters) - Huge reserves of underground water in some of
the driest parts of Africa could provide a buffer against the effects of
climate change for years to come, scientists said on Friday.
Researchers from the British Geological Survey and University College London
have for the first time mapped the aquifers, or groundwater, across the
continent and the amount they hold.
"The largest groundwater volumes are found in the large sedimentary aquifers
in the North African countries Libya, Algeria, Egypt and Sudan," the
scientists said in their paper.
They estimate that reserves of groundwater across the continent are 100
times the amount found on the its surface, or 0.66 million cubic kilometres.
Writing in the journal Environmental Research Letters, they cautioned,
though, that not all these reserves can be accessed.
Where they can, small-scale extraction using hand pumps would be better than
large-scale drilling projects, which could quickly deplete the reservoirs
and have other unforseen consequences.
Groundwater is no panacea for Africa's water shortages but it could form an
important part of a strategy to cope with an expected sharp increase in
demand for water as the continent's population increases.
Even now, some estimates put the number of Africans without access to safe
drinking water at more than 300 million and only 5 percent of arable land is
irrigated.
"It is not as simple as drilling big bore holes and seeing rice fields
spring up everywhere," said Dr Stephen Foster, a London-based senior adviser
for aid group Global Water Partnership and an expert in groundwater issues.
"In some places it could be economically and technically feasible to use
groundwater to reduce crop loss, but I would question whether that is true
everywhere. It will need detailed evaluation.
Foster noted that projects have failed due to cost and logistics problems.
"In northern Nigeria there have been groundwater irrigation projects that
have failed because of the rising cost of fuel - a major factor in drilling
costs - and distribution difficulties."
The researchers say some of the largest deposits are in the driest areas of
Africa in and around the Sahara, but they are deep - at 100 to 250 metres
below ground level.
"Water levels deeper than 50 metres will not be able to be accessed easily
by a hand pump," said the study, led by Dr Alan MacDonald of the British
Geological Survey. "At depths greater than 100 metres the cost of borehole
drilling increases significantly due to the requirement for more
sophisticated drilling equipment."
PUMPING PROBLEMS
The amount of water a borehole yields is another key issue. A small
community hand pump needs a borehole with a flow rate of 0.1 to 0.3 litres
per second. For large-scale irrigation, the rate needs to be much higher,
say around 50 litres.
Phoebe White, a water, sanitation and hygiene specialist for the UK
Department for International Development based in Kinshasa, Democratic
Republic of Congo, said hand pumps in the DRC cost up to $13,000 apiece but
in some areas the aquifers are too deep and other pumps must be used.
In areas of DRC where drilling deep boreholes is required the cost can be
around $130,000, although problems of accessibility and infrastructure can
push that figure up, according to White.
The researchers say the maps, based on existing geological charts from
governments and hundreds of aquifer studies, are aimed at promoting a "more
realistic assessments of water security and water stress".
Roger Calow at UK think-tank the Overseas Development Institute, which was
involved in the programme that spawned the research, said the paper shows
water shortages in large parts of Africa do not stem from scarcity.
"What the science is telling us is that we have more storage in these
shallow, relatively unproductive (aquifers) than we thought," he said,
adding that about 60 percent of Africans still live in rural areas and 80
pct of those rely on groundwater systems.
Calow said a third of hand pumps across Africa have broken down due to a
lack of maintenance.
Aid agencies gave the research a cautious welcome.
"The discovery of substantial water reserves under parts of Africa may well
be good news for the continent but it may prove hard to access in the near
term and, if not sustainably managed, could have unforseen impacts," Nick
Nuttall, spokesman for the United Nations Environment Programme (UNEP) in
Nairobi.
Nuttall said over-abstraction exploitation of groundwater in Mexico City,
for example, is undermining the foundations of buildings.
He said the focus of efforts to improve water supply should be on better
collection and storage.
"The fact is that there is already a tremendous amount of water available
for Africa but it is rarely collected".
A study by UNEP and the World Agroforestry Centre found there is enough
water falling as rain over Africa to supply the needs of some 9 billion
people.
"Ethiopia, where just over a fifth of the population are covered by domestic
water supply and an estimated 46 per cent of the population suffer hunger,
has a potential rainwater harvest equivalent to the population needs of over
520 million people," Nuttall told Reuters. (Additional reporting by Katy
Migiro in Nairobi, Jonnny Hogg in Kinshasa, Mark John in Dakar.Editing by
Jeremy Gaunt.)
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Received on Fri Apr 20 2012 - 10:13:17 EDT
