By 2050 climate change will increase the groundwater deficit even more for four economically important aquifers in the western U.S.
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The new report is the first to integrate scientists' knowledge about groundwater in the U.S. West with scientific models that show how climate change will affect the region.
"We wanted to know, 'What are the expectations for increases and decreases in groundwater as we go forward in this century?'" said lead author Thomas Meixner, a UA professor and associate department head of hydrology and water resources. "In the West, 40 percent of the water comes directly from groundwater."
Climate models predict that in general, wet regions will become wetter and dry regions will become drier. The Southwest is expected to become drier and hotter.
"Aquifers in the southern tier of the West are all expected to see slight-to-significant decreases in recharge as the climate warms," Meixner said.
Groundwater is already being withdrawn from the aquifers of California's Central Valley, the central and southern portions of the High Plains and Arizona's San Pedro faster than the groundwater is being recharged.
Climate change will make the groundwater deficits worse in those aquifers, the researchers report.
For the Death Valley and Wasatch Front aquifers, the effect of climate change on the balance between usage and recharge isn't so predictable.
In contrast, western aquifers at about the latitude of Boulder, Colorado and further north are likely to be recharged faster than people withdraw the water, the team reports. The northern aquifers the researchers studied are the northern High Plains, the Spokane Valley, the Williston Basin and the Columbia plateau.
"In the long term, pumping has to equal recharge. You can get there through slow social adjustment. You could slowly decrease water withdrawal by conservation and efficiency," Meixner said. "Or you can hit bottom and have farm abandonment and dry wells."
"It's a social decision as to who gets the water," Meixner said. "The southern regions of the western U.S. must be prepared to adapt to a much drier future." ■