New research from Arizona State University professors shows the Lower Colorado River Basin has lost as much groundwater as is contained in Lake Mead over the past 20 years.
"We're losing a lot of water," said Jay Famiglietti, an Arizona State University professor in the School of Sustainability.
The study, published this week, used NASA satellites to track water loss both in reservoirs and underground aquifers throughout the Southwest.
“We used NASA-grade satellite data and integrated it with land surface models to assess the groundwater change in the upper and lower Colorado basin,” Karem Abdelmohsen, also with ASU, said.
Even though major Arizona cities are in the desert, there are aquifers underground with millions of acre-feet of water. Famiglietti said most of the groundwater used won't be replenished anytime soon.
"It was deposited underground tens of thousands of years ago, and we have been burning through it in a century,” Famiglietti said.
The research says the losses are due to a combination of drought conditions, increased urban growth demands, and agricultural use throughout the region.
As Colorado River reservoir levels continue to decrease, researchers say just as much, if not more, water is being lost underground, creating a dual crisis for the Southwest's water supply.
Famiglietti believes difficult decisions are coming that will require balancing the Southwest's growing population and economy against current water usage.
“You can only do that for so long,” Famiglietti said. “The challenge is how do we balance the economic growth, the food we need to grow, versus some of the things we don't need to do like farm so much alfalfa and ship it out of the country.”
Mesa Mayor Mark Freeman, who also operates a Valley alfalfa farm, says alfalfa is an important crop to Arizona.
“If you like ice cream, cottage cheese, milk, this is the foundation of where it comes from, for feed and livestock," Freeman said.
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Alfalfa growth contributes hundreds of millions of dollars to the Arizona agriculture economy. The Arizona Farm Bureau estimates that about 20% of it is exported to other countries, but that number has been growing over the years.
Freeman says on his farm in Mesa, water use is closely monitored with specific limitations in place.
"What we do in Mesa and in other municipalities is we bank extra water underground. We're only allowed to pump ‘X’ amount of water from well sites, and they're monitored," Freeman said.
The issue, he says, is that this is not the standard across Arizona and the country, leading to unregulated water pumping.
"In other areas of Arizona, they don't have those guard rails, and there's unlimited pumping," Freeman said.
The ASU-led study and Freeman both say there needs to be better regulation for groundwater pumping in Arizona.
“The active management areas, like Phoenix, Tucson, and Pinal County, still have depletion, but much less than the unmanaged areas,” Famiglietti said. “It really argues for the expansion of that management.”
With Colorado River Basin states currently negotiating new water agreements for after 2026, going forward any cuts could increase pressure on the already decreasing groundwater supply.
"The surface water gets all the policy attention. The groundwater is quietly disappearing," Famiglietti said.
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