Cloud seeding to begin over Sierra Nevada

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    Power agency hopes to improve rainfall totals

    By Charity Maness

    In hopes of giving Mother Nature a helping hand, the Northern California Power Agency will begin its annual cloud-seeding program on Nov. 1 over the North Fork of the Stanislaus River Basin.

    Randy Bowersox, hydroelectric facilities manager for the power agency, said the cloud seeding target area is 74 square miles above New Spicer Meadow Reservoir.

    Cloud seeding is the deliberate introduction into clouds by aircraft, rockets or cannons of various substances, such as salts, calcium chloride, dry ice or silver iodide in an attempt to induce precipitation. A practice that dates back to the 1940s, seeding has been conducted yearly by the NCPA since 2006.

    But according to Bowersox, it isn’t easy determining the efficacy of seeding the Sierra Nevada because of so many variables at work.

    Determining statistically valid “results” is challenging due to natural variability and uncertainty in weather systems, and requires data over an extended time period, Bowersox said.

    He said there are numerous cloud seeding programs over other watersheds on the west slope of the Sierra Nevada, further complicating analysis.

    “Natural variability (like drought) as well as changing global weather patterns add further complications,” Bowersox said.

    In a letter submitted to the Calaveras County Board of Supervisors, Bowersox said the NCPA anticipates “that our weather modification project will yield approximately 3 to 4.5 percent increased augmentation of snow pack.”

    The seeding will continue through May 31 next year “if conditions warrant,” he said.

    If a predicted El Nino weather pattern produces above-normal rainfall or snowpack, the seeding program would be discontinued, Bowersox said.

    Weather Modification Incorporated will be conducting the cloud seeding. This is the same firm that provides aerial cloud seeding services for Sacramento Municipal Utility District, Turlock & Modesto Irrigation Districts, and the University of Nevada, Reno, Desert Research Institute.

    Since its invention in 1946 by American chemist and meteorologist Vincent J. Schaefer, cloud-seeding stories have been woven into history.

    During the Vietnam War, the long-running Operation Popeye from 1967 to 1972, was a U.S. operation that seeded clouds over the Ho Chi Minh Trail with silver and lead iodide to extend the monsoon season.

    After the deadly Chernobyl nuclear disaster, Russians seeded clouds over Belarus in 1986 to stop radioactive particles reaching Moscow.

    Since the launch of the United Nation’s Environmental Modification Convention in 1978, the potential for weather warfare has resulted in 75 countries agreeing not use weather modification for military reasons.

    Still, according to a National Academy of Science study, over 24 countries actively conduct weather modification to improve rainfall.

    In a 2011, Cardno Entrix, an environmental and natural resource management consultant, reported that the U.S. Department of Reclamation, the California Energy Commission and a Mokelumne Lake and Sediment Study were unanimous in their conclusion that silver iodide used in cloud seeding is practically insoluble (will not dissolve in water) and “instead remains in soils and sediments.”

    Soil contamination is one of the leading concerns for ranchers and farmers. Critics of seeding are also concerned about other potential consequences such as potential floods, hail, plant and wildlife mutation, and possible chemical danger to humans consuming water, plants or animals.

    However, the Weather Modification Association (WMA) maintains that use of silver iodide for cloud seeding is safe.

    The WMA noted in their position statement report on the environmental impact on cloud seeding with silver iodide that over 100 Sierra Nevada lakes and rivers have been studied since the 1980s for traceable amounts of silver accumulation. The results of these tests, the WMA said, showed no detectable silver occurring above what naturally occurs in nature to be found in seeded target area water bodies, precipitation and lake sediment samples, “nor any evidence of silver accumulation after more than fifty years of continuous seeding operations.”

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