Much of the country faces severe declines in groundwater even under climate change scenarios with only moderate warming. 

Warmer weather stresses plants, and in response, they rely even more on water supplies just below the surface. And if plants use it all up, it could be gone forever.

University of Arizona researcher Laura Condon says invisible reservoirs under our feet matter just as much as rivers fed by rain and snow.

“We have to think about things that are happening in the subsurface and the water you can’t see, because that can help get us out of droughts and help sustain our water supplies through droughts," she said.

The western U.S. has already seen steep declines in groundwater after decades of pumping. As climate change progresses, Condon says the line dividing the country into the arid West and more humid East could continue moving eastward.