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As people pump groundwater for irrigation, drinking water, and industrial uses, the waterdoesn t just seep back into the ground it also evaporates intothe atmosphere, or runs off into rivers and canals, eventuallyemptying into the world s oceans. This water adds up, and a newstudy calculates that by 2050, groundwater pumping will cause aglobal sea level rise of about 0.8 millimeters per year. Other than ice on land, the excessive groundwater extractions arefast becoming the most important terrestrial water contribution tosea level rise, said Yoshihide Wada, with Utrecht University inthe Netherlands and lead author of the study. In the comingdecades, he noted, groundwater contributions to sea level rise areexpected to become as significant as those of melting glaciers andice 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.His research 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 today inGeophysical Research Letters, a journal of the American GeophysicalUnion. 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 from thegroundwater and the reservoirs would cancel out, Wada said. Wefound that wasn t the case. The contribution from the groundwateris going to increase further, and outweigh the negativecontribution 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,is to improve water efficiency in agriculture to grow more withless groundwater. I am an expert from turbinewheel.com, while we provides the quality product, such as China Jet engine parts , Turbo Kits, Turbine wheels,and more.
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