The rate of water losses in the seven-state Colorado River Basin has tripled in the past decade, mainly due to intensifying groundwater over-pumping in southeast and northwest Arizona, a new study finds.
The study, written by researchers at Arizona State University and elsewhere, explored the magnitude and causes of water losses in rivers and aquifers along with melting snows and moisture in soils.
It concludes that while public and official attention has been mainly focused on the declines in lakes Mead and Powell and other surface water reservoirs, losses of groundwater — to pumping levels far in excess of what is naturally recharged — has been more severe.
Generally, groundwater depletion is a bigger threat to Arizona’s water supplies than the pressures on the Colorado River, said the study’s senior author, ASU Professor Jay Famiglietti.
In a departure from many academic studies, this one takes a nod toward advocacy. It calls for more groundwater management to insure a long-term, sustainable supply. It even suggested federal oversight may be necessary to insure proper state groundwater management.
“The work suggests that, in states like Arizona, where only 18% of the area of the state has groundwater management, that expansion of groundwater management across the entire state is a critical step towards preserving this precious resource for future generations and for long-term economic vitality in the region,” Famiglietti told the Arizona Daily Star in an email.
The current, “patchwork approach to groundwater management in the U.S.” hasn’t been enough to insure long-term sustainability of the groundwater supply, the study says.
“In regions like Arizona and California, where reliance on groundwater is constantly increasing, federal oversight may be necessary to ensure that groundwater resources are effectively managed in conjunction with surface water allocations,” it concludes.
When you look specifically at the Southwestern U.S., “we are running out of water,” said Famiglietti.
A well head stands in a field in Elfrida in the Willcox Basin.
“We need to make sure we preserve the groundwater for our economic security, our food security and our water security,” said Famiglietti, who is with ASU’s School of Sustainability and is also science director of ASU’s Arizona Water Innovation Initiative. “If states aren’t going to do it, the federal government has to come in and encourage states or tell states to do it.”
The study comes as Arizona farmers, other rural residents, environmentalists, county officials and state agency officials and legislators are locked in a seemingly endless dispute over how to create new groundwater regulations for rural Arizona. While everyone involved agrees the state has a problem with unregulated rural pumping, they can’t agree on solutions, particularly on how much farmers should have to cut from their current levels of groundwater pumping.
Specifically, the new study finds, based on data gathered via satellites, computer models and other means, that:
— The entire river basin since 2003 lost nearly 28 million acre-feet of groundwater — roughly the amount of water stored in Lake Mead — to over-pumping; diversions from the Colorado and other rivers; and hotter, drier weather.
— The entire basin lost 2.2 million acre-feet of fresh water annually from 2015-2024. That compared to 690,000 acre-feet a year during the previous decade. The fresh water includes all natural water sources available — groundwater, surface water, melted snows and soil moisture.
— The groundwater losses were driven primarily by increasing groundwater depletion in southeast and western Arizona.
— The lost groundwater represents two-thirds of all the water losses in the basin since 2003. The total water loss figure of 42.3 million acre-feet includes snowmelt and soil moisture as well as groundwater and surface water.
— Most of the total water losses occurred in the drier Lower Colorado River basin. It lost 20.7 million acre-feet of groundwater since 2003. That accounted for 71% of the total water losses in the lower basin in that period, including from surface waters such as the Colorado. Arizona, California and Nevada make up the Lower Colorado basin.
— The hotter, drier Lower Basin states lost far more groundwater during the study period than did the cooler, wetter Upper Basin states of Colorado, New Mexico, Utah and Wyoming.
— Groundwater losses were less in large groundwater basins that also had access to surface water, compared to those with no surface water. Those groundwater basins include the Tucson and Phoenix active management areas, where the state regulates groundwater pumping and where extensive use of Central Arizona Project water in the past few decades has reduced pressure on their aquifers.
The study didn’t break down surface water or groundwater losses by individual states. But the study’s substance and its tone made it clear the authors saw groundwater pumping in Arizona as key sources of the regionwide water losses.
A map included in the study showed that Arizona’s greatest groundwater losses have occurred in southeastern Arizona, centered on the Willcox and Douglas basins, and in La Paz and Mohave counties in west and northwest Arizona. In both areas, out-of-state companies have moved in over the past decade or so and begun pumping large amounts of groundwater to grow alfalfa, other forms of hay and grain, and tree nuts including pecans and pistachios.
Famiglietti said we’re already seeing many of the negative effects of this over-pumping in the form of land subsidence or ground sinking, fissures and drying residential wells. If something isn’t done to better manage aquifers, eventually the groundwater in those areas could become so depleted as to be useless, although he can’t predict when, he said.
“If groundwater remains unprotected in large swaths of the southwestern U.S. and continues to disappear, it will dramatically limit food production,” Famiglietti said. “Groundwater is critically important in desert states like Arizona and desert cities like Phoenix and Tucson, and if it disappears, then it becomes an existential crisis.”
“We are on a very dangerous trajectory. We have to take more action like here in the state of Arizona. I wrote a paper like this 10 years ago and almost uniformly things are getting worse,” he said. “I don’t know what it takes to get people to act.”
In Arizona, legislation to extend groundwater management to rural areas has bogged down in part because Republican opponents of sweeping rural groundwater legislation proposed by Democratic Gov. Katie Hobbs have sought to limit future cuts in groundwater use to no more than 10% from current levels.
Hobbs and other Democrats have backed legislation that would allow cuts of up to 40% over 40 years and accused Republicans in the legislative majority of “stonewalling” the legislation.
But Yuma Republican Sen. Tim Dunn, a key author of less restrictive legislation sought by his party, said the new study doesn’t tell him anything he doesn’t already know: “We’re in a drought. The whole Western U.S. is in a drought.
“When you look at proposing regulations in unregulated areas, limiting someone’s right to pump is a big deal,” said Dunn, noting that the two sides have already agreed to close three groundwater basins including Willcox’s to new pumping. “Something that’s good for Cochise County is not good for the rest of the state.
“There are a lot of details in management as you do these tings, in how it affects cities, utilities and mines. There’s a lot more detail in crafting of this alternative legislation as opposed to just a percentage. We trying to work on a pathway to get there when you are impacting livelihoods, cities and counties,” Dunn said.
Longtime Arizona Daily Star reporter Tony Davis talks about the Colorado River system being "on the edge of collapse" and what it could mean for Arizona.
