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May 28 2025
6Groundwater reserves in the Colorado River Basin have been shrinking at an alarming rate over the past two decades, according to new findings from Arizona State University (ASU). Utilizing satellite data from NASA’s GRACE Follow-On mission, researchers found that the volume of groundwater lost since 2003 is equivalent to the entire capacity of Lake Mead, the largest reservoir in the United States.
The study estimates that approximately 34 cubic kilometers—or 28 million acre-feet—of groundwater has been pumped from the basin since 2003. That figure is more than double the amount of water lost from the Colorado River's reservoirs during the same period.
“The Colorado River Basin is losing groundwater at an alarming rate,” said lead researcher Karem Abdelmohsen from ASU’s School of Sustainability. He explained that the main driver of this depletion is intensive groundwater pumping for agriculture, particularly in the Lower Basin, where desert aquifers supply vast farmlands.
The Colorado River Basin spans parts of seven U.S. states, from Wyoming to Southern California, and northern Mexico. Its water is critical for urban centers like Phoenix and Las Vegas and supports over 5 million acres of farmland. Yet, the researchers found that about 75% of groundwater loss is concentrated in Arizona, where the groundwater is heavily relied upon due to limited surface water availability.
The researchers highlighted that groundwater loss in the basin averages over 1.2 million acre-feet annually—four times the annual allocation of Colorado River water to the Las Vegas area. With river flows diminishing due to persistent drought and rising temperatures, demand for groundwater has intensified.
“Groundwater is a crucial buffer, especially as surface water sources become less reliable,” the study states. However, the aquifers are being drained faster than they can naturally recharge, particularly as climate change exacerbates the region’s aridification.
Jay Famiglietti, senior author and director of ASU’s Arizona Water Innovation Initiative, emphasized the gravity of the situation. “If groundwater remains unprotected in large parts of the Southwest, it poses an existential threat to agriculture and urban life,” he said.
The research team used satellite data alongside measurements of snowpack, soil moisture, and surface water to calculate the groundwater loss. They found that declines below ground are far greater than those seen in surface reservoirs like Lake Mead and Lake Powell, which are currently two-thirds empty.
Despite the severity of the findings, much of the Colorado River Basin still lacks groundwater regulation. In Arizona, 82% of the state’s land has no restrictions on groundwater pumping. While some management efforts exist—such as laws requiring groundwater oversight in areas like Phoenix and Tucson—many rural farming regions remain unregulated.
In southeastern and northwestern Arizona, where groundwater is often the sole source of irrigation, large-scale farms growing water-intensive crops like alfalfa have significantly contributed to the depletion. These regions have experienced some of the fastest rates of groundwater decline.
The consequences are visible: dropping water tables have dried up domestic wells, caused land subsidence, and created surface fissures that damage infrastructure. Famiglietti noted that, unlike in the Upper Basin where groundwater pumping can affect streamflow, the Lower Basin’s deeper aquifers are largely disconnected from river systems, making replenishment even more difficult.
The study’s authors did not prescribe specific policies but suggested their data could guide efforts to curb overuse. One strategy would involve transitioning to less water-demanding crops. Others, like water researcher Brian Richter, argue that permanent reductions in farmland may be necessary to restore balance to the water system.
In California’s Central Valley, where similar groundwater issues have arisen, a 2014 law requires regions to reach sustainability goals by 2040. No such comprehensive law exists in Arizona, though recent moves to establish new groundwater management areas, such as in the Willcox Basin, represent steps toward more oversight.
Satellite data also show that water losses across the Colorado River Basin have tripled from 2015 to 2024 compared to the previous decade, with groundwater accounting for two-thirds of the total depletion.
Richter underscored the urgency of the findings. “We’re losing more stored water underground than we are from surface reservoirs,” he said. “That should be a wake-up call.”
With much of the region’s groundwater dating back thousands of years, depletion on this scale risks making these reserves nonrenewable. As climate change continues to dry the Southwest, experts warn that decisive action is needed to avoid a full-scale water crisis.
“We must come to grips with this great rebalancing act,” Richter said. “Otherwise, we’ll be moving deeper into the danger zone.”
Source:https://phys.org/news/2025-05-groundwater-rapidly-declining-colorado-river.html
This is non-financial/medical advice and made using AI so could be wrong.
