By Andy Tomaswick

Might 27, 2025

Because the Colorado River’s large reservoirs have declined over the last twenty years, even bigger quantities of water have been pumped and drained from underground, in accordance with new analysis primarily based on information from NASA satellites.

Scientists at Arizona State College examined greater than twenty years of satellite tv for pc measurements and located that since 2003 the amount of groundwater depleted within the Colorado River Basin is corresponding to the whole capability of Lake Mead, the nation’s largest reservoir.

The researchers estimated that pumping from wells has drained about 34 cubic kilometers, or 28 million acre-feet, of groundwater within the watershed since 2003 — greater than twice the quantity of water that has been depleted from the river’s reservoirs throughout that point.

“The Colorado River Basin is dropping groundwater at an alarming charge,” stated Karem Abdelmohsen, the lead writer and a researcher at ASU’s Faculty of Sustainability.

The losses are being pushed largely by heavy pumping to provide agriculture, he stated. On the identical time, extended drought and rising temperatures have sapped river flows and decreased the quantity of water percolating underground and recharging aquifers.

“As floor water turns into much less reliable, the demand for groundwater is projected to rise considerably,” the researchers wrote within the examine, which was published Tuesday within the journal Geophysical Analysis Letters. “Groundwater is a vital buffer … however it’s quickly disappearing attributable to extreme extraction.”

The Colorado River Basin covers elements of seven U.S. states, from Wyoming to Southern California, and northern Mexico. The river’s water sustains fast-growing cities together with Phoenix and Las Vegas, in addition to greater than 5 million acres of farmland and ranchland.

The researchers discovered that a lot of the depletion of groundwater (about three-fourths of the whole) is going on within the river’s decrease basin, largely in Arizona, the place the majority of the water is pumped from desert aquifers to irrigate farms.

They estimated that annual groundwater losses within the Colorado River Basin have averaged greater than 1.2 million acre-feet — about 4 instances bigger than the quantity of water the Las Vegas space is entitled to take from the Colorado River annually.

“If this development continues, it might result in extreme water shortages that influence not solely native farmers and residents but in addition broader agricultural markets and municipal water provides all through the southwestern U.S.,” Abdelmohsen stated.

The declines in water provides have worsened as local weather change has intensified drought conditions, driving what scientists describe because the aridification of the Southwest.

Analysis reveals that the previous 25 years have in all probability been the driest quarter-century in western North America in 1,200 years. Scientists have discovered that international warming is intensifying this lengthy megadrought and has triggered roughly half of the 20% decrease within the Colorado River’s common move this century.

“Local weather change is barely exacerbating the stress on groundwater,” stated Jay Famiglietti, the examine’s senior writer and science director for ASU’s Arizona Water Innovation Initiative.

“If groundwater stays unprotected in giant swaths of the southwestern U.S. and continues to vanish, it’s going to dramatically restrict meals manufacturing,” Famiglietti stated. “Groundwater is critically vital in desert states like Arizona and desert cities like Phoenix and Tucson, and if it disappears, then it turns into an existential disaster.”

The researchers used information from a pair of NASA satellites, referred to as GRACE Follow-On, which observe adjustments in Earth’s gravity discipline to measure shifts within the whole quantities of water, each above and under floor. They examined different information on snowpack, floor water and soil moisture to estimate how a lot groundwater has been depleted. They discovered that the losses of groundwater far exceed the declines within the river’s two largest reservoirs, Lake Mead and Lake Powell.

Regardless of this, Famiglietti famous that in giant parts of the Colorado River Basin, groundwater pumping stays unregulated and unmanaged.

“The regular decline of water availability within the Colorado River Basin has been occurring for many years,” he stated. “That the majority of those losses stem from groundwater overuse ought to put states like Arizona on excessive alert, and set off extra pressing dialogue about extending groundwater administration throughout the complete state.”

Efforts to forestall the river’s reservoirs from reaching critically low ranges have attracted widespread consideration and turn into the main target of inauspicious negotiations amongst seven states. With Lake Mead and Lake Powell now two-thirds empty, officers representing California and different states are below rising stress to negotiate a deal to take much less water from the shrinking river.

Much less extensively identified are the rising pressures on the area’s groundwater. Over the past decade, giant farming corporations have expanded in Arizona, planting hay and different water-intensive crops and drilling deep wells in desert areas the place there are no regulations limiting groundwater pumping.

Some residents have been left with dry wells as water ranges have dropped. In locations, collapsing aquifers have caused the land to sink, creating fissures within the floor which have broken roads.

The scientists discovered particularly speedy groundwater losses in elements of northwestern and southeastern Arizona the place large farms irrigate thirsty crops similar to alfalfa, which is used to feed cattle regionally and can be exported to international locations similar to China and Saudi Arabia.

These areas rely closely on groundwater and largely haven’t any entry to water diverted from the Colorado River.

The examine confirmed smaller, but vital, declines in groundwater ranges round Phoenix and Tucson. These areas obtain imported water from the Colorado River by way of the Central Arizona Mission canal, and they’re required to handle groundwater below a 1980 state regulation.

In different analysis, Famiglietti and his colleagues have discovered similar but larger losses of groundwater pushed by agricultural pumping in California’s Central Valley. There, native companies are required below a 2014 state law, the Sustainable Groundwater Administration Act, to curb overpumping and obtain a set of sustainability objectives by 2040.

In Arizona, in distinction, groundwater pumping stays unregulated in 82% of the state. Proposals to guard declining aquifers have repeatedly faced opposition and died within the Legislature, however state regulators final yr fashioned a brand new “active management area” within the Willcox basin in southeastern Arizona, the place they’ve proposed measures to gradually limit agricultural pumping.

Hay is saved on the Fondomonte alfalfa farm in Vicksburg, Ariz., in 2023.

(Caitlin O’Hara / For Washington Submit by way of Getty Pictures)

In elements of the river’s higher basin, groundwater pumping can cut back the move of streams by decreasing the water desk, Abdelmohsen stated. However within the decrease basin, the groundwater lies deeper and is basically disconnected from the river.

The scientists didn’t supply particular suggestions, however they stated their estimates could possibly be used as science-based targets to assist handle overpumping. They stated a method of lowering water utilization could be to shift from water-intensive crops like alfalfa to different crops that use much less.

In a separate evaluation, the researchers discovered that whole water losses throughout the Colorado River Basin have accelerated considerably, with the speed of depletion from 2015-2024 averaging roughly 3 times sooner than from 2002-2014 — a development pushed partly by drying circumstances within the Southwest. Groundwater accounted for two-thirds of the whole losses.

“These scientists are bringing to gentle the unhappy actuality that we’re dropping extra saved water underground than we’re on the floor,” stated Brian Richter, a researcher who was not concerned within the examine. “That tells us that our overconsumption of water within the Colorado River Basin is way worse than I believe a number of us perceived beforehand.”

The area’s desert aquifers comprise water that has been underground for thousands of years. In lots of areas, as soon as these water reserves are exhausted, they’re successfully gone for good.

Along with changing farms to crops that use much less water, Richter stated he believes “we’re going to have to start out speaking about everlasting reductions in agricultural farmland.” He stated laws and federal funds could be wanted to compensate agricultural landowners who conform to take cropland out of manufacturing.

Farmers within the Imperial Valley and different elements of Southern California have lately agreed to leave some fields dry temporarily to assist preserve Colorado River water in alternate for money funds. However they’ve strongly opposed permanent fallowing of land, which they are saying would hurt meals manufacturing and native economies.

Richter stated the newest information counsel extra farmland will have to be left dry to carry water consumption into steadiness with the restricted provide.

“Local weather warming is driving this drying of the Colorado River Basin for the long run, so we actually want to come back to grips with doing this nice rebalancing act,” he stated. “We have to begin transferring out of this hazard zone.”