Scientists at the University of California Center for Hydrologic Modeling in Irvine said water has been disappearing beneath southern Argentina, western Australia and stretches of the United States, ScienceNews.org reported Thursday.
The findings raise concerns farmers are pumping too much water out of the ground in dry regions, researchers said.
"Groundwater is being depleted at a rapid clip in virtually of all of the major aquifers in the world's arid and semiarid regions," hydrologist Jay Famiglietti said.
The drop is especially severe in parts of California, India, the Middle East and China, where expanding agriculture has increased water demand, the researchers said.
"People are using groundwater faster than it can be naturally recharged," Matthew Rodell, a hydrologist at NASA's Goddard Space Flight Center in Greenbelt, Md., said.
Current water use in many areas has become unsustainable, another researcher said.
"There are too many areas in the world where groundwater development far exceeds a sustainable level," Leonard Konikow, a hydrogeologist at the U.S. Geological Survey, said. "Something will have to change."