Groundwater stocks around the world are being depleted at an accelerating rate, according to a research paper soon to be published by the American Geophysical Union. The rate more than doubled between 1960 and 2000, increasing the amount lost from 126 to 283 km³ of water per year.
Today, people are drawing so much water from below ground that they are adding enough of it to the oceans (mainly by evaporation, then precipitation) to account for about 25% of the annual sea-level rise across the planet, the researchers find.
Soaring global groundwater depletion bodes a potential disaster for an increasingly globalized agricultural system, says Marc Bierkens of Utrecht University in the Netherlands, and leader of the new study. He and his colleagues will publish their new findings A Worldwide View Of Groundwater Depletion in an upcoming issue of Geophysical Research Letters.
“If you let the population grow by extending the irrigated areas using groundwater that is not being recharged, then you will run into a wall at a certain point in time, and you will have hunger and social unrest to go with it,” Bierkens warns. “That is something that you can see coming for miles.”
The new assessment shows that the highest rates of depletion are in some of the world’s major agricultural centers, including northwest India, northeastern China, northeast Pakistan, California’s central valley, and the midwestern United States.
“The rate of depletion increased almost linearly from the 1960s to the early 1990s,” says Bierkens. “But then you see a sharp increase which is related to the increase of upcoming economies and population numbers, mainly in India and China.”
As groundwater is increasingly withdrawn, the remaining water “will eventually be at a level so low that a regular farmer with his technology cannot reach it anymore,” says Bierkens. He adds that some nations will be able to use expensive technologies to get fresh water for food production through alternative means like desalination plants or artificial groundwater recharge, but many will not.