A study using NASA satellite data shows many of the world's largest underground aquifers providing fresh water for hundreds of millions of people are being depleted at alarming rates, researchers say.
During the 10-year period of the study, more water was removed from 21 of the world's 37 largest underground aquifers than was replaced, pushing them past their sustainable tipping points, researchers at the University of California, Irvine, say.
Since it is difficult to determine exactly the amount of water that may remain in these aquifers, the danger is that a significant percentage of the world's population is continuing to consume groundwater at a high rate with no chance of any warning of when it might run out, says UCI Professor Jay Famiglietti.
"Available physical and chemical measurements are simply insufficient," says Famiglietti, the principle study investigator who also serves as senior water scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. "Given how quickly we are consuming the world's groundwater reserves, we need a coordinated global effort to determine how much is left."
Data from NASA's Gravity Recovery and Climate Experiment satellites has allowed the first in-depth assessment of the ability of the globe's major aquifers to keep pace with demands from agriculture and the world's ever-growing population, the researchers say.
Underground aquifers are the source of 35 percent of the water used by humans around the world, they point out.
Their assessment does not yield much in the way of good news, they say.
Of particular concern is the finding that the aquifers under the greatest stress are located in regions of the world that are the poorest and most densely-populated, such as North Africa, India and Pakistan.
"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?" asks study lead author Alexandra Richey, who led the research as a doctoral student at UCI. "We're trying to raise red flags now to pinpoint where active management today could protect future lives and livelihoods."
However, the problem of overstressed aquifers is not limited to the poorer parts of the globe, the researchers are quick to point out.
As California reels under the impact of a years-long drought and its rivers and above-ground reservoirs go dry, the state is tapping aquifers in its Central Valley for 60 percent of its water use, a significant increase over the usual 40 percent.
"As we're seeing in California right now, we rely much more heavily on groundwater during drought," Famiglietti says. "When examining the sustainability of a region's water resources, we absolutely must account for that dependence."
Because aquifers are often located in layers of soil or rock at great depths beneath the surface of the Earth, it can be difficult and expensive to drill down to bedrock to find where the water supply bottoms out.
Yet, that's exactly the task the world must undertake, the researchers say.
"I believe we need to explore the world's aquifers as if they had the same value as oil reserves," Famiglietti says. "We need to drill for water the same way that we drill for other resources."
