A source of sea-level rise to rival glaciers

irrigation-768

Groundwater irrigates a field near Mencosta, Mich. A new study finds runoff from groundwater pumping is raising sea levels as much as melting from glaciers and ice caps outside of Greenland and Antarctica. Photo by bnicholephoto/flickr

24 September 2010

New study finds groundwater pumping for irrigation contributes to one-quarter of the sea-level rise observed in today's oceans.

By Douglas Fischer 

Daily Climate editor

Melting glaciers aren't the only reason coastal cities need to worry about sea-level rise.

Agriculture is pumping groundwater for irrigation at such a rate that the runoff equals the contribution from melting of glaciers and ice caps outside of Greenland and Antarctica, according to a new study looking at groundwater depletion.

 It also exceeds or falls into the high-end of previous estimates of groundwater's contribution to sea-level rise, the researchers found.

Most water extracted from underground aquifers ends up in the ocean. The ceaseless pumping contributes about 0.8 millimeters of sea-level rise annually, about a quarter of the 3.1 millimeters per year scientists are observing worldwide, researchers reported. 

depletion-500The study, headed by Marc Bierkens of Utrecht University in Utrecht, the Netherlands, is to be published in an upcoming issue of the journal Geophysical Research Letters, the publication announced Thursday.

The study's main point was to assess the depletion rate of the vast underground stores that billions of people depend on for agriculture and drinking water and that sustain countless streams, wetlands and ecosystems.

The news wasn't good: The depletion rate has more than doubled between 1960 and 2000, with aquifers losing almost 70 cubic miles of water per year.

Because the amount of groundwater is unknown, scientists can't say how fast the global supply will vanish at this point. But if water was siphoned just as rapidly from the Great Lakes, they would go bone-dry in 80 years, according to the study.

"The rate of depletion increased almost linearly from the 1960s to the early 1990s," Bierkens said in a statement. "But then you see a sharp increase which is related to the increase of upcoming economies and population numbers; mainly in India and China."

Groundwater represents about 30 percent of the available fresh water on the planet, with surface water accounting for one percent. The rest of the world's potable, ag-friendly supply is locked up in glaciers or polar ice caps, according to the report.

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Global map of groundwater depletion courtesy American Geophysical Union.

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