Water in the world’s largest aquifers is being pumped out at greater rates than can be replenished naturally. NASA says this poses a greater threat to US food supplies and global security than previously thought.

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Groundwater in the globe’s largest aquifers – the US High Plains, California’s Central Valley, China and India – is being depleted at alarming rates according to new analysis by the NASA Jet Propulsion Laboratory (JPL). The majority of the aquifers lie under the world’s great agricultural regions – and 80 percent of the world’s fresh water usage is in growing crops – meaning their reduction poses a serious threat to the world’s food supply.

“Nearly all of these [aquifers] underlie the world’s great agricultural regions and are primarily responsible for their high productivity,” wrote James Famiglietti, a leading hydrologist at the JPL, in the Nature Climate Change journal. “Vanishing groundwater will translate to major declines in agricultural productivity and energy production, with the potential for skyrocketing food prices and profound economic and political ramifications.”

Analysts used a new software program called Gravity Recovery and Climate Experiment (GRACE), which measures tiny changes in an area’s gravitational pull to determine its groundwater capacity and creates satellite-based images for analysis.

The map below shows the rapidity of depleted groundwater reserves.

“Further declines in groundwater availability may well trigger more civil uprising and international violent conflict in the already water-stressed regions of the world, and new conflict in others,” said Famiglietti.

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The GRACE surveys show, for instance, that the Northwestern India aquifer that straddles the border with Pakistan has been depleted at a rate of 17.7 cubic kilometers a year since 2013.

The Northern Middle East aquifer, meanwhile, loses 13 cubic kilometers a year with Iran, Iraq, Syria and Turkey all pumping water from it.

Two of the United States’ biggest groundwater reservoirs – the Central Valley aquifer in California and the Ogallala aquifer, which stretches from South Dakota to Texas – are losing a combined 15.6 cubic kilometers of water annually due to farmers and cities using up the supply.

Until this study, knowledge about groundwater has been absent because it is not visible like an empty riverbed or dry lake. Also problematic is the lack of data on how much groundwater there is on the planet.

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“Very few major aquifers have been thoroughly explored in the manner of oil reservoirs,” wrote Famiglietti, as reported by Takepart.com. “As a result, the absolute volume of groundwater residing the beneath the land surface remains unknown.”

Famiglietti said this needs to be studied further and agriculture has to be made more efficient.