Cloud seeding: Applied science or alchemy?

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From the High Country News’ Goat blog (Emily Guerin):

Making rain may seem a bit like alchemy, but the practice has been around since the 1940s, when engineers at General Electric began experimenting with dumping dry ice into clouds from airplanes. Water districts and ski resorts around the West got into the practice in the 1970s, shooting silver iodide into winter clouds from mountain-top cannons…

Silver iodide crystals behave like ice, attracting water droplets to them until they grow big enough to fall to the ground as snow. Cloud seeding advocates say the practice is inexpensive—$10-20 per acre-foot of water created—and can boost snowfall by 10 to 15 percent. They’re also quick to point out there are no documented negative environmental effects of the process.

But it’s hard to separate cloud seeding-induced precipitation from what falls naturally from the sky. A 2010 study by Israeli researchers examining rainfall patterns and cloud seeding over the Sea of Galilee in Northern Israel found that a series of cyclones were responsible for increased rainfall over a six-year period, not cloud seeding. The state of Wyoming is currently spending $11 million on a multi-year study to determine whether the practice works and is cost-effective. Results are expected in 2014.

Still, the science is apparently convincing enough for water districts in Southern California, Nevada and Arizona to pay Upper Colorado River Basin states to seed clouds. Since 2006, Lower Basin states have spent over $800,000 in Colorado and around $500,000 in Utah and Wyoming.

More cloud seeding coverage here and here.

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