New research on the world's groundwater supply shows that many of the planet's largest underground aquifers are experiencing depletion.
Of the 37 biggest underground aquifers worldwide, 21 have had more water extracted than replenished over the 2003 to 2013 decade. Those were the years examined for the two new studies, which were based on NASA satellite data and led by the University of California Irvine (UCI).
Thirty-five percent of the world population's fresh water comes from underground aquifers.
The Arabian Aquifer, which supplies water to over 60 million people, is the world's most overstressed underground water basin, researchers found.
In a news release, Alexandra Richey, lead author of the two UCI studies, asked, "What happens when a highly stressed aquifer is located in a region with socioeconomic or political tensions that can't supplement declining water supplies fast enough?"
"We're trying to raise red flags now to pinpoint where active management today could protect future lives and livelihoods," Richey said.
In the United States, the Central Valley Aquifer in drought-stricken California is the most stressed.
"As we're seeing in California right now, we rely much more heavily on groundwater during drought," said Jay Famiglietti, principal investigator of the UCI studies and senior water scientist at NASA's Jet Propulsion Laboratory. "When examining the sustainability of a region's water resources, we absolutely must account for that dependence."
Researchers say climate change and population growth are factors expected to put even more strain on many of the world's aquifers.
It is unknown exactly how much water remains in the world's underground aquifers, meaning it is unclear when the groundwater could run out.
"Available physical and chemical measurements are simply insufficient," Famiglietti added. "Given how quickly we are consuming the world's groundwater reserves, we need a coordinated global effort to determine how much is left."