The Nature researchers found that the most severe depletion is concentrated "in a few regions that rely significantly on overexploited aquifers to grow crops, mainly the USA, Mexico, the Middle East and North Africa, India, Pakistan and China, including almost all the major breadbaskets and population centres of the planet."
The group mapped global food trade flows from these areas with the most-stressed aquifers—places like the California Central Valley, the Midwest’s High Plains (where farmers have for years been draining the Ogallala aquifer to grow corn and cotton), India’s breadbasket, the Punjab, and China’s main growing region, the North Plain.
Note that the group was looking at data from a period just before the onset of California’s recent drought (2011-2016), which triggered a massive frenzy of water-pump drilling and an epic drawdown of aquifers.
The new study underlines a point I’ve made before: Water reserves in California’s Central Valley are in a long-term state of decline—aquifer recharge during wet years never fully replaces all that was taken away during dry times.
Of those seven countries that use massive amounts of water from dwindling aquifers to grow crops, just three are major exporters of those crops: the United States, Mexico, and Pakistan.
They also looked at countries that rely most on imported food grown with fossil water.
The researchers found that a "vast majority of the world’s population lives in countries sourcing nearly all their staple crop imports from partners who deplete groundwater to produce these crops, highlighting risks for global food and water security."
Along with Mexico, Iran, and China, the researchers placed the United States among a handful of countries that are "particularly exposed" to the risks of groundwater scarcity "because they both produce and import food irrigated from rapidly depleting aquifers."
The paper isn’t trying to make the point that food trade is somehow bad.
Rather, it’s that global food trade hinges increasingly on a vanishing resource, and that the water footprint of our food supply is largely invisible to both end consumers and policymakers.