Independent researchers studying the Colorado River say the federal plan for reducing water deliveries to Arizona, California, and Nevada would force cutbacks on a scale the region has not faced before.
For Arizona communities that depend on the river — especially around Phoenix and Tucson — that could mean a much harder and more expensive path to keeping water flowing to homes and businesses.
Here's what to know
The paper, as KJZZ reported, says the Lower Basin proposal would reduce supplies by about two-fifths a year from 2028 through 2036.
Arizona leaders had already worked out a shorter-term plan with cuts of about 20% for 2026 and 2027, but they remain deeply concerned about the steeper reductions that could follow.
Jack Schmidt, a co-author of the report who has spent years researching the river at Utah State University's Center for Colorado River Studies, called the potential reductions a "really, really big number."
Rising temperatures, prolonged drought, and steady demand from the seven states that use the river are all intensifying pressure on the Colorado. After those states could not agree on their own path for future cutbacks, the federal government put forward its own proposal.
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At the highest end of the proposal, Lower Basin use would drop below a benchmark built by combining the lowest-use month from each year in the 17-year analysis, bringing annual totals down to levels "not seen since 1935," KJZZ said.
More background
In Arizona, the Central Arizona Project canal system primarily serves cities and suburbs around Phoenix and Tucson.
If those supplies decline sharply, city leaders say water can still keep reaching taps, but the fixes will cost a lot.
Even before any new rules take effect, the Lower Basin has already been using relatively little water. Schmidt said, "To achieve those kind of cuts would be completely unprecedented in the Lower Basin. We're not arguing that it should or shouldn't be, but we're saying — don't kid yourself, those are unprecedented numbers, and the economic impacts of implementing those kind of very large numbers, for which there's no historical analogy, would be very serious issues."
What's being done?
One of the biggest debates is whether the burden should be shared more evenly.
KJZZ reported that the federal approach would leave the Upper Basin states — Colorado, Utah, Wyoming, and New Mexico — without mandatory cuts, even as Lower Basin users are being asked to make historic reductions.
Schmidt said, "The fact that those magnitude cuts are without historical precedent leads me to think that there's no way you can ask the Lower Basin to make those magnitude cuts and not ask the Upper Basin to do anything."
The study also identified areas where additional water savings may still be possible, especially in agriculture.
In Southern California's Imperial Irrigation District, the report said additional conservation could come from reducing summer irrigation for field crops such as alfalfa while still protecting winter vegetable production.
Since 2022, the authors found, Colorado River use through the Central Arizona Project has fallen 40%, while the rest of Arizona's users — mostly farms — have reduced use by just 6%.
"You're going to have to find a way in Arizona to reduce the sum of those other users," Schmidt said. "You can't have a system where all the cuts are being taken by CAP and the other users' line just sort of stays flat."
Where can I learn more?
Arizona's water worries are tied to a much bigger dispute over who absorbs Colorado River shortages and how states make up for dwindling supplies. This coverage helps explain why officials are warning about steep delivery cuts, looking for backup sources, and fighting over the river's long-term future.
• Across Arizona, California, and Nevada, 40% water cuts could begin under the federal proposal.
• Arizona is pursuing a Pacific desalinated water swap to backstop future Colorado River losses.
• Federal officials have extended 18 crucial agreements meant to steady management of the Colorado River.
Keeping water flowing to Phoenix and Tucson will require more than conservation alone. Decisions made across the basin could shape costs and water security for millions of people in Arizona.
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