The water's edge (Image: George Steinmetz/Corbis)
Nearly all our fresh water comes from obscure underground
deposits – now satellites and radioactive isotopes are telling us how
much we have to go round
Deep
beneath the eastern Sahara, the Nubian Sandstone aquifer was in
trouble. By the early 2000s, the aquifer - one of the largest and
oldest groundwater deposits in the world, which supplies Libya, Egypt,
Chad and Sudan - was emptying fast. Egypt was tapping the aquifer to
feed its growing desert cities far from the Nile. Libya, whose only
other water source is the salty Mediterranean, was drawing water off by
way of an underground network of pipes and aqueducts known as the Great
Man-Made River, which Libyans describe as the eighth wonder of the
world.
Soon
the Sahara's oases began to dry up, causing water shortages for nomadic
groups and wildlife. But no one could agree on who was to blame. The
ancient aquifer system was just too complicated: it was impossible to
pinpoint who was taking too much water, or even estimate when it would
run out.
Because
none of the countries trusted the others to provide an unbiased
analysis, they couldn't agree on what steps, if any, to take to protect
the aquifer. Mistrust and a lack of cooperation threatened to spiral
into something worse.
This
conflict exposed an ordinary truth that had somehow been forgotten:
most of the world's drinking water is hidden underground, and we don't
have a clue what's happening to it. But as global populations grow and
climate change kicks in, one thing is certain: we can no longer count
on the water to be where we expect to find it. Our groundwater is
dissipating into the ocean, being consumed at record rates and being
irreversibly contaminated; even as claims to what remains become
increasingly contentious. It won't be long before shortages cause
widespread droughts and the first water war begins.
How
can we stop this? The first step is knowing where the water is.
Conventional maps are no longer enough when you're dealing with an
invisible, moving target. But there is hope. Impressive new physics and
engineering tools are beginning to yield the first clear pictures of
the world's hidden water. These have already revealed some unexpected
good news, but their real promise is in the possibility of a world map
of a resource more precious than oil.
Although it comprises 97 per cent
of the world's accessible fresh water - the UN Environment Programme's
latest estimate - we have never really bothered to get a clear picture
of the water beneath our feet. Most hydrologists prefer to study the
water on the Earth's surface. "Certainly groundwater has suffered from
an 'out of sight, out of mind' problem," says Peter Gleick, a
hydroclimatologist who runs the Pacific Institute, an independent
think-tank based in Oakland, California.
Most
people would be surprised to hear that. After all, it's been easy
enough to exploit the water hidden in aquifers. These underground
stores are vast; the 40,000 cubic kilometres of water in the Guarani
aquifer in South America, for example, far exceeds what's in all five
of North America's Great Lakes. But this water isn't held in a vast
underground lake. Instead, it moves, often slowly, through complex
layers of permeable rock, sand and other geology. And unlike a lake,
how useful it is depends not only on how much water it contains, but on
how quickly it is refilled by rainwater or snowmelt.
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