Groundwater depletion rate more than doubled in recent decades: Study

WASHINGTON - After a global assessment of groundwater use, scientists have suggested that groundwater depletion has more than doubled in recent decades.

Today, people are drawing so much water from below that they are adding enough of it to the oceans (mainly by evaporation, then precipitation) to account for about 25 percent of the annual sea level rise across the planet, found researchers.

Soaring global groundwater depletion bodes a potential disaster for an increasingly globalized agricultural system, said Marc Bierkens of Utrecht University.

“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,” warned Bierkens.

Bierkens and colleagues compared estimates of groundwater added by rain and other sources to the amounts being removed for agriculture and other uses, the team taps a database of global groundwater information including maps of groundwater regions and water demand.

The researchers also use models to estimate the rates at which groundwater is both added to aquifers and withdrawn. For instance, to determine groundwater recharging rates, they simulate a groundwater layer beneath two soil layers, exposed at the top to rainfall, evaporation, and other effects, and use 44 years worth of precipitation, temperature, and evaporation data (1958-2001) to drive the model.

Applying these techniques worldwide to regions ranging from arid areas to those with the wetness of grasslands, the team found that the rate at which global groundwater stocks are shrinking has more than doubled between 1960 and 2000.

The new assessment has shown the highest rates of depletion 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.

“But then you see a sharp increase which is related to the increase of upcoming economies and population numbers; mainly in India and China,” said Bierkens.

As groundwater is increasingly withdrawn, the remaining water “will eventually be at a level so low that a regular farmer with his technology cannot reach it anymore,” he added.

The findings were published in the Geophysical Research Letters, a journal of the American Geophysical Union. (ANI)