Golden State Weather Warriors
California, parched by drought and shrinking mountain snowpacks, hopes cloudseeding (yes, cloudseeding) could help quench its driest year on record.

A small flurry of “who knew?” news reports accompanied last week’s opening of California’s annual cloudseeding season. The Sacramento Bee, in a widely distributed feature, outlined active weather modification projects in 15 California watersheds, citing a state report estimating that cloudseeding adds 400,000 acre-feet of water annually to California’s reserves—enough to supply three out of every ten households in the Bay Area for a year. The San Jose Mercury News noted that water managers across the state fear the impacts of drought, and with good reason: San Francisco has just experienced its driest year on record. Grist quickly weighed in, opining that cloudseeding was “certainly not a real fix for climate change.”

Perhaps not, but Jeff Tilley, director of weather modification at the Desert Research Institute, welcomed the public’s apparent embrace of cloudseeding as a weapon in the war on drought, declaring: “The message is starting to sink in that this is a cost-effective tool.”

If so, the sinking-in has been a long time coming. As I reported in the Fall 2013 issue of OnEarth, the practice of seeding clouds with silver iodide to increase rain or snowfall was pioneered by GE in 1946 and has been in use ever since, particularly in the arid West. Utilities in California started seeding high Sierra watersheds in 1948. Today there are weather modification programs operating in ten Western states, including hail reduction efforts in North Dakota, rain enhancement in Texas and Kansas, and snowpack augmentation in Wyoming, Idaho, Colorado, Utah, and Nevada.

But California remains perhaps the best example of how cloudseeding can potentially help fight droughts. Not only is the state perpetually in need of more water, but its geography and climate come together to make cloudseeding over the Sierra Nevada especially effective. Moisture-laden clouds roll off the Pacific and hang up on the Sierra’s peaks. Those clouds represent an untapped water resource if they don’t precipitate on their own.

Contrary to science fiction and conspiracy theories, rainmakers cannot “make rain.” What they can do is help existing clouds precipitate. Clouds do not always release their stored water vapor—in fact the majority of it never falls, partly because water droplets in clouds are often supercooled, meaning they remain liquid even at temperatures well below freezing. Without forming ice crystals, they are too tiny to fall. “Rainmaking” provides a nucleus to which the cloud’s supercooled water droplets can adhere until they grow heavy enough to fall to the ground as rain or snow. Silver iodide, with a crystalline structure similar to that of water, is most commonly used; it is aerosolized and dispersed via burners on the ground or mounted on airplanes.

Weather modifiers call what they do “precipitation enhancement,” and declare that it bolsters cloud efficiency—sometimes “downstream” as well as in the target area. It does not, as many fear, rob Peter to pay Paul, though public understanding of that fact has lagged behind the science from the beginning. (As reader comments on some of the articles noted above demonstrate, there’s no shortage of ill-informed paranoia about weather modification.)

Immediately after inventing the process in 1946, GE scientists teamed up with the military on Project Cirrus, an ambitious series of cloudseeding experiments aimed at ending droughts, controlling snowfall (more for ski resorts, less for cities), preventing forest fires, averting hail, and even busting hurricanes. The popular press, caught up in the excitement, announced the dawn of a new era of weather control. Man was finally going to do something about the weather.

That never happened. Concerned about legal ramifications and unclear profit potential, GE got out of weather control in the early fifties, and although a series of government and private experiments ensued, the irrational exuberance of weather modification’s early years caused the shadow of junk science to blight it for decades. By the eighties, interest had died down so much that even the U.S. Bureau of Reclamation—whose motto is “Managing Water in the West”—largely ceased work in the field. Rainmakers point out that this lack of enthusiasm coincided with an exceptionally wet period in the United States. They have a saying for this phenomenon: “Interest in cloudseeding is soluble in rainwater.”

There’s no shortage of ill-informed paranoia about weather modification.

Today, however, as climate uncertainty grows, the West languishes in an epic drought, and wildfires rage, interest in cloudseeding is resurgent. A rigorous study being done in Wyoming, spearheaded by the National Center for Atmospheric Research, will publish its results in summer 2014. At the annual meeting of the Weather Modification Association this year, a scientist on the study reported that they expect to report precipitation increases of around 10 percent, with 95-percent confidence, in seeded clouds. That’s not quite a climate-control bonanza. But it is significant to states that depend heavily on water stored in mountain snowpacks. And for states making hydropower from run-off, 10 percent more water through their turbines adds up to real money.

Weather modification strikes some people as creepy, a form of tampering with nature. But in a state where hydro projects have already dammed and diverted all the state’s major rivers, turned a breathtaking valley into a reservoir, made a dust bowl of a former inland sea, and—by accident—created the state’s largest lake, wringing a little extra precipitation from the winter clouds seems minor in comparison.

Cloudseeding will not, of course, solve California’s water problems. What it should do is draw attention to the fact that our rapid development of the West, with no regard for the drain on its natural resources, is already forcing us to take extreme measures—and things are only getting worse.

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