Research shows that groundwater in the Colorado River Basin is falling rapidly.
As the giant reservoirs of the Colorado River declined over the past two decades, even pumping water from the ground and draining more water, according to NASA satellites.
Arizona State University scientists examined two decades of satellite measurements and found that since 2003, the amount of groundwater depleted in the Colorado River basin has rivaled the total capacity of Lake Mead, the largest reservoir in the United States.
Researchers estimate that since 2003, pumping water from the water has drained about 34 cubic kilometers, or 28 million acres-foot of groundwater, more than twice the amount of water consumed from the river.
“The Colorado River Basin is losing groundwater at a shocking rate,” said Karem Abdelmohsen, lead author of the ASU School of Sustainability.
He said the loss was driven mainly by a large amount of water pumping to supply agriculture. At the same time, prolonged droughts and temperature rises reduce rivers and reduce water in the underground and charged aquifers.
“As surface water becomes less reliable, the demand for groundwater is expected to increase significantly,” the researchers wrote in the study. “Groundwater is a crucial buffer…but it is rapidly disappearing due to overextraction.”
The Colorado River Basin covers part of seven states from Wyoming to Southern California and northern Mexico. The river’s water maintains fast-growing cities including Phoenix and Las Vegas, as well as more than 5 million acres of farmland and pasture.
The researchers found that most of the depletion of groundwater (about three-quarters of the total) occurs in the river’s lower basin, mainly in Arizona, where most of the water is pumped from desert aquifers to irrigate the farm.
They estimate that the annual groundwater loss in the Colorado River Basin averages more than 1.2 million acres, about four times the amount of water the Las Vegas region is entitled to take up from the Colorado River each year.
“If this trend continues, it can lead to severe water shortages that will affect not only local farmers and residents, but also the wider agricultural market and municipal water supply throughout the Southwest,” Abdul Molson said.
As climate change occurs, the decline in water supply has intensified Strengthen drought conditionspromote what scientists call the aridity of the southwest.
Research shows that the past 25 years may be The driest quarter century 1200 in western North America. Global warming is exacerbating such a long giant Morgan About half of 20% decrease in the average flow of the Colorado River this century.
“Climate change only increases the pressure on groundwater,” said Jay Famiglietti, senior author and scientific director of Arizona Water Innovation Intiative at ASU, the study.
“If groundwater remains unprotected in blockbusters in our southwest and continues to disappear, it will greatly limit food production,” Famiglietti said. “In desert countries like Arizona and desert cities like Phoenix and Tucson, groundwater is crucial, and if it disappears, it will become an existential crisis.”
The researchers used data from a pair of NASA satellites, called GRACE TOSTON, which tracks changes in Earth’s gravity field to measure changes in the total amount of water on and below the ground. They examined other data on snow accumulation, surface water and soil moisture to estimate how much groundwater was exhausted. They found that the loss of groundwater far exceeded the decline of Lake Mead and Lake Powell, the two largest reservoirs in the river.
Nevertheless, Famiglietti notes that groundwater pumping remains unregulated and unmanaged in much of the Colorado River Basin.
“The continued decline in water in the Colorado River Basin has been going on for decades,” he said. “Most of these losses stem from excessive groundwater use, which should put states like Arizona on high alert and spark more urgent conversations about extending groundwater management across the state.”
Efforts to prevent reservoirs of river water to reach critical levels have attracted widespread attention and have become the focus of difficult negotiations in seven states. With Lake Mead and Lake Powell now two-thirds empty, officials representing California and other states are under increasing pressure Negotiating a deal Take less water from the shrinking river.
Less well known is the growing pressure on groundwater in the region. Over the past decade, large agricultural companies have expanded in Arizona to grow hay and other water-intensive crops and drill deep wells in desert areas No regulations restrict groundwater pumping.
Some residents have Leave a dry well As the water level drops. In some places, the aquifer has Causes land to sinkcreate cracks on the ground that damages the road.
Scientists find that groundwater losses are particularly fast in parts of northwestern and southeast Arizona Irrigate thirsty crops on farms For example, Alfalfa Feed the cattle Locally, it is also exported to countries such as China and Saudi Arabia.
These areas rely heavily on groundwater and largely do not obtain water transferred from the Colorado River.
The study showed that groundwater levels around Phoenix and Tucson were smaller but significantly lower. These areas receive imported water from the Colorado River through canals in central Arizona, and under state laws of 1980, they must manage groundwater.
In other studies, Famiglietti and colleagues found Similar but greater losses Groundwater powered by agricultural pumping in the central California valley. There, must be in the local agency Laws of 2014The Sustainable Groundwater Management Act to curb excessive tilt and achieve a set of sustainability goals by 2040.
By comparison, in Arizona, groundwater pumping remains unregulated in 82% of states. Proposals to protect the aquifer collapse repeatedly Facing the opposition and died in the Legislature, but last year the state regulator formed a new “Actively manage the area“In the Wilcox Basin in southeast Arizona, they proposed measures Gradually restrict agricultural pumping.
Hay is stored in 2023 at Fondomonte Alfalfa Farm in Vicksburg, Arizona.
(Caitlin O’Hara / The Washington Post via Getty Image)
In parts of the upper river basin, groundwater pumping can reduce the flow of streams by lowering groundwater levels, Abdulmosen said. But in the lower basin, the groundwater is deeper and is largely disconnected from the river.
Scientists did not provide specific advice, but they said their estimates could be used as science-based goals to help address excessive tilt. One way to reduce water use, they say, is to transfer from water-intensive crops such as alfalfa to other less-used crops.
In another analysis, the researchers found that total water loss across the Colorado River Basin has accelerated significantly, with depletion starting from 2015-2024 faster than the average 2002-2014 than the 2002-2014, a trend driven partly by dry conditions in the Southwest. Groundwater accounts for two-thirds of the total loss.
“These scientists are revealing a pathetic reality that we are losing more groundwater underground,” said researcher Brian Richter, who is not involved in the study. “It tells us that we have a much worse overwater in the Colorado River Basin than I think a lot of us think.”
The desert aquifers in the area contain already Thousands of years underground. In many areas, once these water reserves are exhausted, they effectively disappear.
Richter said that in addition to converting farms into crops that use less water, he believes “we will have to start talking about permanent reductions in agricultural farmland.” He said legislation and federal funds will be needed to compensate agricultural land owners who agreed to withdraw farmland from production.
In recent years, farmers in Empire Valley and other parts of Southern California have agreed Make some fields temporarily dry Help protect the Colorado River water in exchange for cash. But they strongly oppose permanent recreation of the land, which they say will harm food production and local economy.
Richter said the latest data suggests that more farmland needs to be dried to balance water supply with limited supply.
“Climate warming is driving this dryness in the Colorado River Basin, so we really need to master this excellent rebalancing behavior,” he said. “We need to start leaving this dangerous area.”
