Half of the world's biggest aquifers are being depleted

In two new studies, a team of researchers led by hydrologists from the University of California, Irvine assessed the depletion of groundwater on a global scale using readings from NASA's GRACE satellites. The satellites monitor changes in Earth's gravity and act as a "scale in the sky," measuring shifts in the total amounts of water, both above and below ground. They concluded that likely much less water remains in aquifers than previously estimated. Groundwater is the primary source of water for about 2 billion people.

Over half of the world's biggest aquifers are being depleted. They are past sustainability tipping points, and a third of those big aquifers - 13 of those - are seriously distressed. The most severe situations seen in dry areas where little or no water is seeping into the ground to offset the amounts pumped out. The researchers found the Arabian Aquifer System, which supplies water to more than 60 million people, to be the most overstressed in the world, followed by the Indus Basin aquifer of northwestern India and Pakistan, and the Murzuk-Djado Basin in northern Africa, the Canning Basin in Australia and the aquifer system of the North China Plain. The aquifer beneath California's Central Valley was labeled as highly stressed. The Ogallala Aquifer didn't show up as being in decline, overall, even though portions of it likely have only a few decades of water left.

These problems can be addressed with proper management strategies, including replenishing aquifers when possible, recycling wastewater and adopting water-saving irrigation techniques.