What to do when the rain won’t come? If you’re California, you seed the clouds. At least that’s what water managers, utilities and ski-resort operators in the state are hoping to do this winter. 2013 was the driest year on record for the Golden State. So officials there plan to spray silver iodide into the clouds in an effort to squeeze every last possible snowflake out of them and replenish state water resources.
Cloud seeding has been around for almost 70 years now, since Vincent Schaefer, a self-taught chemist, dumped six pounds of dry ice into the clouds over the Berkshire Mountains in Massachusetts in 1946, making them snow. The experiment led to speculation that cloud seeding could fight drought, control storms, reduce hail and quench forest fires.
Indeed, today about 10 states, mostly in the West, have cloud-seeding operations to combat such conditions. In Arizona, California, Colorado, Idaho, Nevada, Utah and Wyoming, cloud-seeders are hired to increase the snowpack. In Kansas and Texas, they work to induce rain, and in North Dakota, they induce rain before the clouds can produce crop-damaging hail.
Cloud seeding is the process of spreading either dry ice or more often silver iodide into the upper part of clouds to try to stimulate the precipitation process and form rain or snow. With the recent glut of extreme droughts, floods, forest fires and other adverse weather conditions, interest in cloud seeding is growing. Jeff Tilley, director of weather modification at the Desert Research Institute (DRI), part of the Nevada system of higher education, told the San Francisco radio station KQED that the practice of cloud seeding has become more and more scientifically robust over the last 10 to 15 years. “As a result, we now know much more about how to seed clouds properly,” he said, “what techniques work under what conditions.”
But while the technology is better, there is still a dearth of good evidence on whether cloud seeding really works, or what, if any, the long-term consequences are of altering nature. There does seem to be a general consensus that cloud seeding isn’t harmful to the environment. The amount of silver iodide used is so little, according to the Centers for Disease Control and Prevention, that there is no reason to fear any toxic effects. As for complaints that cloud seeding robs Peter to pay Paul: Weather experts say there’s not a shred of evidence that shows cloud seeding affects snow and rainfall downwind of specific areas.
The biggest debate is over how much extra water cloud seeding actually generates. The DRI estimates that cloud seeding produces about a 10 percent increase in snowpack. A 2013 report by the California Department of Water Resources estimated an average snowpack increase of just 4 percent.
That lack of certainty is one reason why the weather modification world is eagerly awaiting the results of a Wyoming study to be completed later this year. The state has invested $13 million since 2005 in a project to determine whether cloud seeding really increases the amount of snowpack in several of the state’s mountain ranges. It is the first rigorous and comprehensive study of the field, and many believe it will bring new credibility to cloud seeding.
Similarly, Colorado recently asked cloud-seeding programs in the state to do more stringent target and control evaluations, comparing seeded areas with comparable geographic areas that aren’t targeted.
Cloud seeding isn’t a panacea for water woes, but it’s one of the cheaper solutions. The National Resources Defense Council (NRDC) reports that building and operating a desalination plant, for example, costs between $1,000 and $2,000 for every acre-foot of water it yields. Cloud seeding, on the other hand, yields that same acre-foot of water for $5 to $15.
But it is not the cheapest. In NRDC’s magazine, OnEarth, senior policy analyst Robert Moore said, “As it gets hotter and drier, efficient use of water is the cheapest and most reliable way of making more of it available for future use,” he said. “In the energy world, the cheapest kilowatt of electricity is the one you never have to generate. The same goes for water. The cheapest gallon of water is the one you never take from the tap.”