Groundwater Pumping Raises Sea Levels

Article excerpt

As people pump groundwater for irrigation, drinking water, and industrial uses, the water doesn't just seep back into the ground--it also evaporates or runs off into rivers and canals, eventually emptying into the world's oceans. This water adds up, and a new study calculates that by 2050, groundwater pumping will cause a global sea level rise of about 0.8 millimeters per year.

"Other than ice on land, the excessive groundwater extractions are fast becoming the most important terrestrial water contribution to sea level rise," said Yoshihide Wada of Utrecht University in the Netherlands and lead author of the study. In the coming decades, he noted, groundwater contributions to sea level rise are expected to become as significant as those of melting glaciers and ice caps outside of Greenland and the Antarctic.

Between around 1970 and 1990, sea level rise caused by groundwater pumping was cancelled out as people built dams, trapping water in reservoirs so the water wouldn't empty into the sea, Wada said. His research shows that starting in the 1990s, that changed as populations started pumping more groundwater and building fewer dams.

The researchers looked not only at the contribution of groundwater pumping, which they had investigated before, but also at other factors that influence the amount of terrestrial water entering the oceans, including marsh drainage, forest clearing, and new reservoirs. Wada and his colleagues calculate that by mid-century, the net effect of these additional factors is an additional 0.05 mm per year of annual sea level rise, on top of the contribution from groundwater pumping alone.

The research team's article was published in Geophysical Research Letters, a journal of the American Geophysical Union.

The last report of the United Nations Intergovernmental Panel on Climate Change in 2007 addressed the effect on sea level rise of melting ice on land, including glaciers and ice caps, Wada said. But it didn't quantify the future contribution from other terrestrial water sources, such as groundwater, reservoirs, wetlands and more, he said, because the report's authors thought the estimates for those sources were too uncertain. …