24 September 2010
Groundwater depletion accelerating worldwide
by Kate Melville
A new assessment of the planet's subterranean reservoirs shows the highest rates of depletion in the world's major agricultural centers, including northwest India, northeastern China, Pakistan, California and the Midwestern United States. The depletion rate has doubled in recent decades and study author Marc Bierkens, of Utrecht University in the Netherlands, warns of a looming disaster for an increasingly globalized agricultural system.
These fast-shrinking subterranean reservoirs are essential to daily life and agriculture in many regions, but people are drawing so much water that it accounts for about 25 percent of the annual sea level rise across the planet, Bierkens notes.
"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."
Bierkens' work, published in Geophysical Research Letters, uses a database of global groundwater information as well as various computer models to estimate the rates at which groundwater is both added to aquifers and withdrawn. Applying these techniques worldwide to regions ranging from arid areas to those with the wetness of grasslands, Bierkens and his fellow researchers found that the rate at which global groundwater stocks are shrinking has more than doubled between 1960 and 2000. The amount lost each year has increased from 126 to 283 cubic kilometers (30 to 68 cubic miles) during the same period. The total amount of groundwater in the world is unknown, so Bierkens can't say when supplies will vanish.
Groundwater represents about 30 percent of the available fresh water on the planet, with surface water accounting for only one percent. The rest of the potable, agriculture friendly supply is locked up in glaciers or the polar ice caps. This means that any reduction in the availability of groundwater supplies could have profound effects for a growing human population.
"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As groundwater is increasingly withdrawn, the remaining water; "will eventually be at a level so low that a regular farmer with his technology cannot reach it anymore," says Bierkens.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 desalinization plants or artificial groundwater recharge, but many won't.
Source: American Geophysical Union