Many of America’s critical sources of underground water are in a state of rapid and accelerating decline, a new study has found.
More than half of the aquifers in the United States (53 percent) are losing water, according to research published on Wednesday in Nature.
And in about 1 in 8 American aquifers — roughly 12 percent — the collapse of underground water levels has sped up during the 21st century, the researchers found.
“Groundwater levels are declining rapidly in many areas,” coauthor Scott Jasechko of the University of California Santa Barbara told The Hill.
“And what’s worse, the rate of groundwater decline is accelerating in a large portion of areas,” Jasechko said.
The impacted aquifers support much of the U.S. food system, as well as providing water used by many Americans. And the country is not alone in its losses: The study found rapid loss of water in aquifers that supply hundreds of millions of people worldwide.
But the researchers added that these grim findings came with a bright spot: many once-declining regions have bucked the trend
“Long term groundwater losses,” they wrote, “are neither universal nor inevitable.”
Hydrologists talk about aquifers in terms of “shallowing” and “deepening” — that is, is whether groundwater is getting closer to or further from the surface.
When it came to the global trend of shallowing, the prime culprit the researchers identified was agriculture: 70 percent of global withdrawals of underground water went toward irrigation.
This helps explain declines in aquifers that support large amounts of U.S. agriculture and cities — particularly the breadbaskets of California’s Central Valley and the dairies and alfalfa farms of Arizona’s Gila Bend.
“We’re finding that in dry places where a large portion of the land is under cultivation, groundwater level declines are if anything accelerating over time,” Jasechko said.
But agriculture isn’t the whole story. The researchers found another pattern in regions where groundwater declines were accelerating: less water entering the system.
Regions where there had been a decrease in rain and snowfall in the early 21st century — compared to a wetter late 20th century — were more likely to see their aquifers declining faster than places where rainfall had held constant.
This suggests a dual cause of loss — less rain entering the system to recharge the aquifers, which also drove farmers to turn to groundwater to make up for what precipitation and surface water no longer provides.
As groundwater losses accelerated, so too did their impacts, the researchers wrote.
Some of the problems caused by a shallowing aquifer are obvious: For one, wells — which after all are holes drilled down into the groundwater – begin to run dry.
“Wells are only so deep,” Jasechko said. As groundwater levels deepen, “they get rendered useless for extracting groundwater.”
But this is only the beginning. As an aquifer deepens further into the earth, structural problems begin to arise, Jasechko said.
The aquifers beneath our feet can be thought of as colossal water balloons pressing upward on the land and water — boosting up rivers, lakes and creeks so they stay on the surface, keeping the sea at bay and giving structure to the ground.
But as the balloon begins to sag, that structure fails in turn. Creeks and rivers leak into the ground and disappear into the space left as groundwater levels fall. Sinkholes open up in the land.
And in areas along the coast, seawater begins to move inward, fouling water supplies, killing crops and sickening ecosystems.
The staggering variety of potential external factors that shape these impacts — whether an aquifer is surrounded by saltwater, for example — make it hard to come up with uniform, hard and fast rules about what constitutes an alarming rate of decrease, coauthor Debra Perrone told The Hill.
But 24 U.S. basins experienced groundwater declines greater than about 0.5 meters per year (around 18 inches), or what the Nature team called “rapid deepening” – nearly 60 percent of which were in California.
To an outsized extent, the problems identified in the Nature study are — for Americans at least — problems of California, and of the national food systems’ reliance on the fertile Sacramento and San Joaquin Valleys and the groundwater beneath.
More broadly, they are problems that connect to the declining supplies of water from the overallocated and diminishing Colorado River — a body of water that serves roughly 40 million people across the American West and is still divvied up based on the much-higher levels it attained in the cooler, wetter climate of the early 20th Century.
As that river has declined and the population that relies on it has surged, municipalities and commercial agriculture alike have become ever more dependent on groundwater — a trend that has led to a rash of dry wells in states like Arizona, where the Willcox-Douglas Basin is currently dropping by more than a foot per year.
But Nature researchers noted that the Colorado River has also been the silent partner in two successful attempts to bring underground water sources back from decline — though they questioned how long these projects could last.
West of Tucson, Arizona, water managers diverted excess water from the Colorado River to the Avra Valley, allowing it to filter back into the underground aquifer of the same name — a once-declining, thousands-year-old water source that is now regaining about half an inch of water per year.
And in New Mexico, a channel connects the Colorado River to the San Juan, a tributary of the Rio Grande — enabling Albuquerque to meet more of its municipal needs with surface water, and relieving pressure on groundwater reserves like the Albuquerque or Palomas Basin, which are now recovering by about an inch per year.
But these gains are fragile, Jasechko said, and he’s skeptical of their long-term viability.
“I think it would be generous to call diversion from the Colorado River to other water-stressed areas a solution,” he said, adding that further diversions from the overpromised waterway were “likely to be noticed.”
More promising, he said, is a plan in Arkansas, where — amid broader overpumping from aquifers across the state — the community of El Dorado has drastically cut its use of groundwater thanks to a two-step solution.
First, county officials began charging a fee for pumping groundwater — which
in turn helped incentivize local industry to the nearby Ouachita River a few miles away, which helped take the strain off of underground wells.
Thanks to those reforms, El Dorado and its surrounding county stand out as a bright spot amid the generally dismal state of Arksansas groundwater, according to a 2023 state report.
Compared to the state as a whole, the Sparta aquifer under El Dorado “experience[d] the most recovery, having the greatest average change in the five and ten-year intervals,” the state report found.
Several wells in the area saw up to 17 meters (56 feet) of shallowing, or recovery, in the past decade — or according to the Nature study, a steady gain of more than 0.05 meters (2 inches) per year.
Because it relies on pulling water from one basin to another, Jasechko said, this solution, too, is potentially fraught — though “it’s possible that there’s adequate surface water in river to meet needs of ecosystems and communities that depend on that river.”
One element of the Arkansas plan, which is rather unusual for the United States, has been very successful in other countries.
That’s Union County’s decision to charge groundwater users a fee for what they pump — as opposed to many Western jurisdictions, where scarce and irreplaceable groundwater can offer a back door irrigation source for agriculture, industry and homeowners unable to get access to highly regulated creeks, lakes and rivers.
But an example from Bangkok, Thailand, suggests that when water is less free, people are less free with it.
In 1994, with sinkholes opening and land sinking across the sprawling city, the metropolitan government imposed a fee of up to $.21 for every cubic meter (about four bathtubs) pumped by industrial users — a fee that was higher if water was taken for more sensitive areas.
This was added to an additional $.21 to be paid by everyone who used groundwater — meaning that “in the most critical areas industrial and commercial groundwater users could be paying a total of $0.42″ per cubic meter, according to a World Bank summary.
In conjunction with these fees, the government began a strict campaign of fines and legal punishments for illicit well construction — and sealed wells that were drilled without permission.
Thanks to all this, the city — which was once sinking in places by about .10 meters (4 inches) per year — is now declining by less than an inch, and aquifers that had deepened to more than 55 meters (180 feet) has now shallowed back to 40 meters (130 feet).
This approach, Jasechko suggested, offers a model for water stressed U.S. regions — if they’re willing to take the time.
That, he told The Hill, was the biggest thing about his findings that surprised him: that given “clever, locally relevant interventions, with adequate scope and scale — we can make things better.”
“Groundwater depletion is not inevitable,” he said.
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