Less than 6% of ground water in the upper two kilometres of the Earth’s landmass is renewable within a human lifetime, according to a new map showing the world’s hidden groundwater.
“This has never been known before,” said the study’s lead author, Dr Tom Gleeson of the University of Victoria in Canada.
“We already know that water levels in lots of aquifers are dropping. We’re using our groundwater resources too fast ~ faster than they’re being renewed.”
Using data and computer models, an international group of hydrologists has produced the first data-driven estimate of the Earth’s total supply of groundwater.
The study (subscription access only) published in the journal Nature Geoscience estimated the total volume of underground water to be almost 23 million cubic kilometres, of which just 0.35 million cubic kilometres is younger than 50 years old.
Underground water is found beneath the Earth’s surface and is recharged by rain, snow or water that leaks from the bottom of lakes and rivers.
Its age can be a few months to millions of years. It can be found as deep as nine kilometres, according to the United States Geological Survey.