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"Other than ice on land, the excessive groundwater extractionsare fast becoming the most important terrestrial water contributionto sea level rise," said Yoshihide Wada, with UtrechtUniversity in the Netherlands and lead author of the study. In thecoming decades, he noted, groundwater contributions to sea levelrise are expected to become as significant as those of meltingglaciers and ice caps outside of Greenland and the Antarctic. Between around 1970 and 1990, sea level rise caused by groundwaterpumping was cancelled out as people built dams, trapping water inreservoirs so the water wouldn't empty into the sea, Wada said. Hisresearch shows that starting in the 1990s, that changed aspopulations started pumping more groundwater and building fewerdams. The researchers looked not only at the contribution of groundwaterpumping, which they had investigated before, but also at otherfactors that influence the amount of terrestrial water entering theoceans, including marsh drainage, forest clearing, and newreservoirs. Wada and his colleagues calculate that by mid-century,the net effect of these additional factors is an additional 0.05 mmper year of annual sea level rise, on top of the contribution fromgroundwater pumping alone. The research team's article is being published May 9 in Geophysical Research Letters , a journal of the American Geophysical Union. The last report of the United Nations Intergovernmental Panel onClimate Change in 2007 addressed the effect on sea level rise ofmelting ice on land, including glaciers and ice caps, Wada said.But it didn't quantify the future contribution from otherterrestrial water sources, such as groundwater, reservoirs,wetlands and more, he said, because the report's authors thoughtthe estimates for those sources were too uncertain. "They assumed that the positive and negative contribution fromthe groundwater and the reservoirs would cancel out," Wadasaid. "We found that wasn't the case. The contribution fromthe groundwater is going to increase further, and outweigh thenegative contribution from reservoirs." In the current study, the researchers estimated the impact ofgroundwater depletion since 1900 using data from individualcountries on groundwater pumping, model simulations of groundwaterrecharge, and reconstructions of how water demand has changed overthe years. They also compared and corrected those estimates withobservations from sources such as the GRACE satellite, which usesgravity measurements to determine variations in groundwaterstorage. With these groundwater depletion rates, Wada and his colleaguesestimate that in 2000, people pumped about 204 cubic kilometers (49cubic miles) of groundwater, most of which was used for irrigation.Most of this, in turn, evaporates from plants, enters theatmosphere and rains back down. Taking into account the seepage ofgroundwater back into the aquifers, as well as evaporation andrunoff, the researchers estimated that groundwater pumping resultedin sea level rise of about 0.57 mm in 2000 -- much greater than the1900 annual sea level rise of 0.035 mm. The researchers also projected groundwater depletion, reservoirstorage, and other impacts for the rest of the century, usingclimate models and projected population growth and land usechanges. The increase in groundwater depletion between 1900 and2000 is due mostly to increased water demands, the researchersfind. But the increase projected between 2000 and 2050 is mostlydue to climate-related factors like decreased surface wateravailability and irrigated agricultural fields that dry out fasterin a warmer climate. If things continue as projected, Wada estimates that by 2050, thenet, cumulative effect of these non-ice, land-based water sourcesand reservoirs -- including groundwater pumping, marsh drainage,dams, and more -- will have added 31 mm to sea level rise since1900. The new study assumes that, where there is groundwater, people willfind a way to extract it, Wada said, but some of his colleagues areinvestigating the limits of groundwater extraction. One way todecrease groundwater's contribution to sea level rise, he noted, isto improve water efficiency in agriculture -- to grow more withless groundwater. We are high quality suppliers, our products such as Bicycle Trike Parts Manufacturer , China Bathroom Partitions Hardware for oversee buyer. To know more, please visits Custom Machined Parts.
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