By Janet Raloff
Pumping groundwater, some 70 percent of it to irrigate crops, has recently become a potent force in global sea-level rise, two new studies conclude.
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It sounds obvious: Once brought to the surface, water will eventually run into the seas, says hydrologist Yoshihide Wada of Utrecht University in the Netherlands. But until now, most major assessments of factors affecting sea-level rise — such as those reported by the Intergovernmental Panel on Climate Change — ignored the role of groundwater extraction, he says. For instance, the IPCC has assumed that groundwater extraction would be largely balanced by river water impounded by dams.
Such an assumption was probably accurate until about 1980, says Yadu Pokhrel of Rutgers University in Piscataway, N.J. Since then, the balance has shifted, he says, and groundwater extraction is now developing into a growing force behind sea-level rise.