Planes will release silver iodide crystals in the Tuolumne County high country if a cloud-seeding project is approved by the U.S. Bureau of Reclamation later this year. Plans call for the project to commence this winter. The proposed five-year Walker River Basin Cloud Seeding Project is a continuation of cloud-seeding efforts in the central Sierra Nevada going back to 1992.
Planes have been releasing silver iodide crystals over Tuolumne County — the flight area includes the Stanislaus National Forest, Emigrant Wilderness and Yosemite — during much of that time. The planes are at work in the county generally from November to April. The seeding process works like this: The tiny silver particles hover in the air and serve as a condensation surface for water vapor, which eventually leads to rain or snowfall. A public comment period for an environmental assessment of the project ends Aug. 27. The ultimate target of the cloud-seeding project is Nevada’s Walker Lake, some 60 miles away as the crow flies from Pinecrest Lake, which sits at the northern tip of the proposed flight pattern. The goal is to increase the eastern Sierra snowpack and runoff into Walker River, which feeds Walker Lake. Jane Schmidt, of the Bureau of Reclamation’s Carson City, Nev., office explained that Walker River diversions for irrigation purposes have reduced flows into Walker Lake. “The lake has been in serious decline for some time,” she said. Specifically, according to the Nevada Wildlife Federation, the reduced flows have shrunk the lake’s shoreline and increased its salt and pollutant levels. This, in turn, has killed fish in the lake, including the endangered Lahontan cutthroat trout.
In 2009, the nearby town of Hawthorne canceled its Loon Festival because the lake, once a major stop for migratory loons, could no longer provide enough small fish to attract the birds. In addition to the cloud-seeding effort, Schmidt noted that conservation groups are working on plans to secure water rights that would allow more water to be fed into the dying high-desert lake.
The cloud-seeding, she said, is simply a supplementary effort that alone cannot make up for the lost inflows to Walker Lake. Indeed, studies from The Desert Research Institute — a nonprofit branch of the Nevada college system, which plans to do the cloud-seeding — show that cloud seeding in the central Sierra Nevada has resulted in a 2 percent to 10 percent increase in snow-water levels.
The difficulty with cloud seeding is it’s nearly impossible to determine how much snow would have fallen without the effort. Addressing concerns the public might have about the safety of the $1.4 million project, Schmidt said the cloud-seeding in Tuolumne County is scheduled to take place around 14,000 feet — 3,000 feet higher than area peaks — and the silver iodide used in the cloud-seeding formula has not been detected in streams and soils following years of seeding. “We’re talking parts per trillion,” she said.
In addition, seeding doesn’t “steal” water from the Western Sierra Nevada to fuel precipitation in the Eastern side of the range, according to Smith. That’s because the silver iodide is placed in areas where the wind is already carrying moist air to the eastern side, she said. Accusations of “stealing rain” are common in China — the world’s largest cloud-seeder — where, in many places, rockets are fired into the air to disperse silver iodide and bring precipitation to dry areas.
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