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Scientists
say the notoriously dry continent of Africa is sitting on a vast reservoir of
groundwater.
They argue
that the total volume of water in aquifers underground is 100 times the amount
found on the surface.
The team
have produced the most detailed map yet of the scale and potential of this
hidden resource.
Writing in
the journal Environmental Research Letters, they stress that large scale
drilling might not be the best way of increasing water supplies.
Across
Africa more than 300 million people are said not to have access to safe
drinking water.
Demand for
water is set to grow markedly in coming decades due to population growth and
the need for irrigation to grow crops.
Freshwater
rivers and lakes are subject to seasonal floods and droughts that can limit
their availability for people and for agriculture. At present only 5% of arable
land is irrigated.
Now
scientists have for the first time been able to carry out a continent-wide
analysis of the water that is hidden under the surface in aquifers. Researchers
from the British Geological Survey and University College London (UCL) have
mapped in detail the amount and potential yield of this groundwater resource
across the continent.
Helen
Bonsor is from the BGS is one of the authors of the paper. She says that up
until now groundwater was out of sight and out of mind. She hopes the new maps
will open people's eyes to the potential.
"Where
there's greatest ground water storage is in northern Africa, in the large
sedimentary basins, in Libya, Algeria and Chad," she said.
"The
amount of storage in those basins is equivalent to 75m thickness of water
across that area - it's a huge amount."
Ancient
events
Due to
changes in climate that have turned the Sahara into a desert over centuries
many of the aquifers underneath were last filled with water over 5,000 years
ago.
The
scientists collated their information from existing hydro-geological maps from
national governments as well as 283 aquifer studies.
The researchers
say their new maps indicate that many countries currently designated as
"water scarce" have substantial groundwater reserves.
However,
the scientists are cautious about the best way of accessing these hidden
resources. They suggest that widespread drilling of large boreholes might not
work.
Dr Alan
MacDonald, lead author of the study, told the BBC: "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 hand
pumps are likely to be successful."
With many
aquifers not being filled due to a lack of rain, the scientists are worried
that large-scale borehole developments could rapidly deplete the resource.
 |
| African water supplies may be more resilient to climate change than was thought |
According
to Helen Bonsor, sometimes the slower means of extraction can be more
efficient.
"Much
lower storage aquifers are present across much of sub-Saharan Africa," she
explained.
"However,
our work shows that with careful exploring and construction, there is
sufficient groundwater under Africa to support low yielding water supplies for
drinking and community irrigation."
The
scientists say that there are sufficient reserves to be able to cope with the
vagaries of climate change.
"Even
in the lowest storage aquifers in semi arid areas with currently very little
rainfall, ground water is indicated to have a residence time in the ground of 20
to 70 years." Dr Bonsor said.
"So at
present extraction rates for drinking and small scale irrigation for
agriculture groundwater will provide and will continue to provide a buffer to
climate variability."
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