(The Hill) — A heating planet and expanding commercial agriculture are putting increasing pressure on America’s vital aquifers — underground reservoirs that supply water to an estimated 145 million Americans, as well as supporting much of the nation’s food supply.
New research published Tuesday in Nature uncovered rapid and accelerating declines in underground water sources across the world, with some of the fastest and most significant collapses impacting aquifers that supply the American West.
Researchers told The Hill that declines aren’t inevitable, and that they can be reversed — but doing so requires a clear understanding of where the losses are happening, and what is driving them.
Based on the data gathered by the scientists behind the Nature study, here are six states where the collapse of groundwater supplies poses the biggest challenge.
The collapse of groundwater reserves beneath California’s Central Valley stands out as particularly severe — even among all the global losses.
The state, which has for years struggled with drought, depends more heavily on its underground water stores than any other in the country: Currently, California accounts for 21 percent of total groundwater usage in the U.S., and draws about 67 percent of its fresh water from its groundwater reserves.
That reliance is taking a toll: Of California’s 183 groundwater basins evaluated by the Nature team, three-quarters are in decline — and for many, that decline is occurring very quickly.
The most significant of the losses are hitting the state’s Central Valley — a result of 25 percent of the nation’s agriculture being concentrated in less than 1 percent of its area, in a region that combines near-desert aboveground conditions with rich reserves of underground water that have accumulated over thousands of years.
Or at least, once-rich reserves.
The Nature team considered groundwater “deepening” — or the dropping of groundwater levels further into the earth — to be rapid when it surpassed 0.5 meters, or 19 inches, per year.
The team found that 15 of California’s basins showed rapid decline — virtually all of which are beneath its Central Valley.
For five of these, decline was particularly fast: Water levels were dropping at more than a meter a year (36 inches) in the Cuyama Valley, White Wolf Basin, San Pasqual Valley, Chowchilla Basin and Northern Kern Basin.
Of these, the Cuyama Valley — where farms, homes and businesses alike must draw all their water from wells — is experiencing particularly quick losses of 1.45 meters (almost 5 feet) per year.
But all five of these rapidly depleted areas are part of the San Joaquin Valley, which accounts for half of California’s agricultural production.
That connection isn’t a coincidence. Eighty percent of the groundwater California uses goes to agriculture, according to data from the United States Geological Survey (USGS).
Both for Central Valley farms and for the rest of California, the state’s reliance on underground water stores poses a particular concern as its other water sources are becoming ever more scarce: The Colorado River, the source of 15 percent of the fresh water California doesn’t get from groundwater, is declining, and a heating planet is pushing the state’s vital snowpack — a kind of water battery that slowly drips water down into the lowlands that would otherwise disappear into flash floods — higher and higher into the mountains.
While the aquifers beneath Texas don’t face the level of critical collapse that California’s do, the hot, dry Southwestern state is also facing a thirsty century
According to the Nature researchers’ data, 82 percent of Texas’s aquifers are in some form of decline. Of these, one — Lobo Flat, the site of a ghost town that once thrived when the water did — is in rapid decline, losing 0.6 meters (23 inches) per year.
Another, the Edwards-Trinity or High Plains aquifer, is just below that threshold, with annual losses of 0.45 meters (just under 18 inches).
As The Hill reported in 2022, that region has faced the twin onslaughts of drought and a boom in water-hungry dairies — both of which have put added pressure on the already declining aquifers, and stirred fears about agriculture in the Texas High Plains coming to an end.
While the story for most state aquifers is a more protracted decline than punctuated drop-off, in more than a quarter of Texas’s underground basins — 28 percent — groundwater loss is speeding up. Levels in those basins are receding at twice the rate in the 21st century as they did at the end of the 20th.
In some, the decline is accelerating even faster than that.
One example: the Edwards Aquifer, which supplies the expanding subdivisions sprouting up on the old cattle ranches in the hills west of the state capital of Austin — and its old colonial capital of San Antonio.
In the 1990s, that pumping was already taking its toll, with water levels dropping 0.06 meters (2 inches) per year. But in this century it’s expanded threefold to losses of 0.17 meters (about 7 inches) per year — enough that the region’s beloved springs are beginning to go dry.
This state has the dubious honor of hosting the fastest collapsing aquifer in the Nature researchers’ dataset: the Mill Creek Aquifer, which is losing 2.17 meters (more than 7 feet) of water per year — a serious concern for the 200,000 people who rely on it for drinking water.
While Mill Creek is the only aquifer in Idaho experiencing rapid decline, levels are falling in 60 percent of the state’s other groundwater stores, and in 11 percent of them that decline has more than doubled since the last century.
As elsewhere, this decline is driven by farming. Despite having a population of less than 2 million, Idaho accounts for 6 percent of the nation’s total groundwater usage, 92 percent of which it puts toward crops and livestock.
The driving forces behind Arizona’s water woes are a mix of those causing the losses in California and the Texas High Plains: declines in the Colorado River, which supplies Arizona with more than a third of its water, booming cities and an agriculture industry that is growing thirsty crops such as alfalfa using sparsely regulated groundwater.
With surface water supplies diminishing and rain famously scarce in the desert, 41 percent of Arizona’s water supply comes from wells — and according to the Nature study, 70 percent of these are in decline across the state.
One farming region, the Gila Bend Basin, has become a “top priority” for state water managers due to the precipitous collapse in its aquifer levels, which have fallen nearly 300 feet since the 1990s.
According to the Nature researchers’ data, that basin has seen 1.21 meters (47 inches) of deepening per year — marking the most dramatic decline in any of the state’s basins, but far from the only one.
Another basin, the Ranegras Plain aquifer, is showing deepening rates just a bit under the rate of rapid decline, according to the Nature study.
While state water managers have attempted to create rural water management districts to regulate the pumping of groundwater, so far they haven’t been able to so much as get a committee hearing in Arizona’s conservative Legislature — though they are trying again this week.
For now, Utah’s big cities can rely on the snowmelt that comes off the Wasatch Front, which looms above the urban corridor that includes Salt Lake City — a metropolis that gets just 10 percent of its water from underground.
But the state as a whole depends on groundwater to meet 60 percent of its water needs — of which 80 percent is consumed by agriculture.
Under pressure from both growing cities and irrigation, 82 percent of Utah’s aquifers are in a state of decline — 11 of them at twice the rate of last century.
Two of these deepening aquifers, the Parowan and Goshen Valley, are declining at either just above or just below the rate the Nature researchers consider rapid.
Coincidentally, neighboring New Mexico has exactly the same share of declining aquifers — 82 percent — though they are not failing at quite the same rate as in Utah.
These declines are concerning because like California, Utah can expect its patterns of precipitation to change as the climate heats up — and while more water may fall from the sky than does currently, a greater share will fall as easily lost rain, rather than the steady, reliable drip of snowpack.
Despite Mississippi’s position beside the enormous river that gives the state its name, groundwater provides its residents with 82 percent of their fresh water.
That level of dependence on underground water is unparalleled in the eastern U.S. And it’s exacerbated by the fact that farmers and cities in neighboring states — from the rice farmers of Arkansas to the city of Memphis, Tenn. — depend on many of the same subterranean reservoirs.
One of these in particular — the Middle Claiborne, which stretches in a vast rounded triangle from Jackson, Miss., to Memphis almost to Little Rock, Ark., but was owned by Mississippi — was the cause of a suit between Mississippi and Memphis that reached the Supreme Court in 2021.
In that case, Mississippi complained that Memphis’s use of the Claiborne water beneath Tennessee was sucking its own resources dry — forcing the high court to determine whether aquifers were governed by the same rules as interstate surface river basins like the Colorado.
It ruled they were, and that the two states must share the water by equitable apportionment. But Mississippi has less and less to share.
According to the Nature researchers’ data, 57 percent of the state’s aquifers are in decline. The part of the Middle Claiborne that lies just outside Jackson, Miss., is dropping by 0.72 meters (28 inches, or a little more than two feet) per year.
That decline is sufficient to make the Jackson region’s artesian wells — those that bubble forth on their own from water pressure beneath — stop flowing entirely, according to 2023 research by one of the Nature study’s co-authors.
As agriculture is the primary driver of this decline, the U.S. Forest Service has proposed one possible solution for the region: turn marginal croplands back into forests.
A 2021 study found that areas with new forests on them lost groundwater at one-eighth the rate of croplands — which Forest Service scientists ascribed to the fact that after the trees were planted, no more groundwater pumping was being pumped to prop up “less productive croplands.”
While these states are facing particularly urgent water crises, many of their neighbors are experiencing widespread declines of their own.
In Oklahoma, where more than half of state water comes from underground, 82 percent of aquifers are in decline.
That share of decline is matched by New Mexico, where 7 state aquifers are dropping at more than twice the rate they were in the late 20th century.
And in Kansas, where 71 percent of water comes from groundwater, 65 percent of state aquifers are deepening.
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