On the high plains of Texas, tens of thousands of wells pumping from the 10-million-year-old Ogallala Aquifer have reduced the water content by 50 percent.
Most of the remaining underground water source will probably be useless within about 30 years.
Katharine Hayhoe, professor and director of the Climate Science Center at Texas Tech University in Lubbock, says big changes are on the way for agriculture on the Great Plains.
"We're seeing major shifts in places and times we can plant, the types of crops we can grow and the pests and diseases we're dealing with.
"There's no question we can adapt to some of the change, but whether we can adapt to all of it is a very open question."