The board that oversees water delivery to Phoenix and Tucson has decided to stop paying into a program that seeds mountain storms hundreds of miles away in hopes of squeezing out a little extra snow for the Colorado River. On Nov. 5, the Central Arizona Project board voted 8-6 not to renew its funding agreement for the multi-state cloud-seeding effort, ending more than a decade and a half of participation in the collaborative program.
CAP had contributed about $447,000 to the program in Wyoming, Colorado and Utah the prior year, and would have been on the hook for up to $525,000 in the coming year, with that cap rising gradually to $750,000 by 2036, according to azcentral.com. The program sprays silver iodide molecules into advancing Rocky Mountain storms in an effort to squeeze more precipitation out of the clouds, the outlet reports. CAP has been part of the collaborative cloud-seeding effort since 2007, according to KJZZ, and the agency runs a 336-mile canal system that carries Colorado River water across the desert into the Phoenix and Tucson areas.
Board members who voted against renewing the funding raised doubts about what the money actually buys. Azcentral.com reports there was as yet no clear evidence of how much of that water ultimately flowed into Lake Powell, a concern board members voiced directly during deliberations. CAP board members also cited the difficulty of measuring impact as a reason for their skepticism, per the station's reporting, with one member saying it is difficult to measure exactly how much of an impact they're getting from the money they're spending.
A Program With Mixed Scientific Backing
The vote taps into a broader scientific debate that has simmered for decades. Research on cloud-seeding effectiveness has produced mixed results over roughly 70 years, according to Colorado State University. Most studies of seeding cumulus clouds have shown little to no effect, the university notes, while studies of wintertime orographic seeding — the kind used in the Rockies, where clouds form as air rises over mountains — have shown increases in precipitation.
Estimates of how much that translates to in snowpack vary widely depending on the measure. CAP staff have said studies suggest cloud seeding can boost the snowfall of a given storm by 10% or more, the station's report notes, while a 2015 study cited by Colorado State University found conditions in Wyoming were right for seeding only about a quarter of the time from November through April, with a likely seasonal snowpack increase of no more than about 1.5%. A separate account from KJZZ states that scientists estimate cloud seeding can contribute up to 20% more snow during some individual storms, but typically only about 5% to 15% over a full winter season.
How Other States Compare
Utah offers a useful comparison for the program's upside. The state's extension service estimates that where cloud seeding is used, it enhances local snowpack by 3% to 13%, according to Utah State University Extension. Utah has run its own program for more than 50 years and now operates more than 170 cloud-seeding generators, with seeding used during 184 storm events statewide in the 2023–2024 winter, including 20 events that involved aerial seeding by aircraft, the extension service reports. Utah also receives about $500,000 annually from Arizona, California and Nevada for cloud seeding, per the same source.
The economics can look compelling on paper. A 2018 study of Utah's program found that cloud seeding could create an acre-foot of water for less than $3, according to Inside Climate News, compared with more than $3,000 per acre-foot at the Colorado River basin's largest desalination plant. Arizona, California and Nevada water agencies together have sent about $1.5 million per year to upstream cloud-seeding work in recent years, per KJZZ's earlier reporting on the program.
A Vote Shaped by a Larger River Feud
The funding decision landed amid a multi-year standoff among Colorado River states over how to divide a shrinking water supply, according to azcentral.com's reporting. That dispute, between lower basin states and their upstream counterparts, has left the river's long-term management plan unresolved even as CAP's board weighed whether a faraway snow-boosting program was worth the cost. Whether that tension directly shaped individual votes isn't addressed in the available reporting, but the two issues were unfolding on parallel tracks as CAP reconsidered its commitment.
For now, the Phoenix-area utility has stepped back from a cloud-seeding partnership it joined nearly two decades ago, leaving the program's remaining backers — and the open questions about where that extra snow actually ends up — to carry on without CAP's share of the bill.
