Idaho Power briefs Senate committee on collaborative cloud seeding program, cites snowpack gains and safety studies

Cresta Davis, senior manager of water resources at Idaho Power, told the Senate committee the company’s collaborative cloud seeding program aims to augment winter snowpack to benefit irrigation, hydropower, aquifer recharge and fish and recreation.

Davis said Idaho Power’s program now uses 63 remote ground generators and three aircraft stretching from western Wyoming through the Payette Basin, and that the program’s estimated average annual benefits by basin are roughly: Boise Basin 240,000 acre-feet, Wood River Basin just over 100,000 acre-feet, Upper Snake Basin about 600,000 acre-feet and Payette Basin close to 200,000 acre-feet — totaling just over 1 million acre-feet across the Snake River Basin. Davis reported an approximate cost of about $4 per acre-foot when program costs are spread across beneficiaries.

Explaining the method, Davis said cloud seeding in Idaho targets snowpack enhancement and relies primarily on silver iodide as an artificial ice nucleus; the program also added liquid-propane ground generators in 2024. She described the propane generators as a cooling mechanism that “acts to cool the air as it passes,” allowing supercooled liquid water to adhere to particles and form snow. On the scientific and environmental record, Davis cited studies including Solak et al. (2003), North American Weather Consultants and work summarized by the Weather Modification Association and Australia’s Natural Resource Commission. She said those studies — and more than 20 others — found no evidence of environmentally harmful effects or human health impacts from the silver iodide concentrations used in cloud seeding.

On potential downrange impacts, Davis said target-control analyses show increased precipitation not only within target areas but in some cases downstream; she cited studies finding up to a 14% increase within targets and smaller increases up to hundreds of kilometers downrange. She also described suspension criteria used by the program — developed with state and federal partners and reviewed annually — that halt seeding if snowpack or reservoir conditions exceed thresholds to avoid increasing flood risk.

Committee members asked technical questions. Sen. Taylor asked whether propane or silver iodide is emitted; Davis replied propane cools the air while silver iodide provides the nucleation surface. Senators also asked whether silver iodide is measurable in local water samples; Davis said Idaho Power’s sampling could not detect program-related silver above background levels and that naturally occurring background levels exceed any program contribution. Several senators noted Idaho’s hydroelectric-heavy generation mix and the importance of reliable water supply to the state’s power system; Davis said cloud-seeding is one tool to help sustain hydropower as other resources are added to the grid.

No formal action was taken in the hearing; the item was a presentation and Q&A.

Ending: Committee members thanked Idaho Power and closed the session. The record shows the company will continue coordination with state agencies and local water users and that monitoring, suspension criteria and annual benefit analyses are part of the ongoing program.