Scientists say 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.
NIGER DESERT (REUTERS) - 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.
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.
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 unforeseen consequences.
Florence Sylvestre, research director at the Research Institute for the Hydro-Paleoclimatology Development, warned that although there was a great deal of water under the continent, much of it is what is regarded as fossil water that has been under ground for thousands of years.
"These aquifers, from what we know today, contain water that comes from the period of the green Sahara. So, we should know that these aquifers, at least that underneath lake Chad, it's a collection of subterranean layers separated by sediments. The deepest aquifer contains fossil water. We know that there was a great period of refill, during the holocene period, between 6,000 and 8,000 years ago, at the time we think the Sahara was green," she said.
Sylvestre said the problem was that if the water is accessed, it may not be replenished, so may not be available for long-term use.
"The big question is if it's still being supplied with water, because effectively they could be usable resources for the population provided that we could build wells sufficiently deep to reach it. But the big question is if these waters are still being replenished given the dryness context, and at what rate," she said.
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.
In Niger, water is already a scarce commodity according to well builder Mahamane Moutari Harouna.
"We build wells in a way that the population and the livestock have access to water. You see, we are in a Sahelian country and access to water is a rare commodity, it's really like gold in certain areas of the country," he said.
With the population growing Harouna said that there will be a time when people in Niger will have no choice but to access fossil water.
"I think these are water layers for the future. Its time hasn't come yet. Not now. Maybe in the next few years, when the population will rise, because you see Niger has a very high population density, and it rises at a high rate of 3.4 percent per year, which is a lot for Africa. Soon we will be forced to go look for water there where we can find it, so down there, in the fossil water layers," he added.
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.
And drought is still a problem - the Horn of Africa experienced its worst drought in 60 years in 2011, whilst Lake Chad, which provides livelihoods for about 30 million people in surrounding countries, has shrunk to a tenth of what it was in the 1960s.
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