Sidebar by Allen Best
Cloud-seeding – April 2004 – Colorado Central Magazine
Random experiments will help Denver decide whether to continue cloud seeding
In pioneer days promoters of homesteading in the arid West said that rainfall follows the plow. While there is little evidence that those promoters were right, it can be said conclusively that cloud seeding follows drought.
After Colorado’s last major drought, in the winter of 1976-1977, cities, ski areas, and agricultural water districts across the state scrambled to buy the “insurance” of weather modification. But gradually interest fell off, particularly after 1983-84, years that were so wet that Glen Canyon Dam nearly washed away without assistance from Edward Abbey and his Monkey Wrench Gang. Since then, while ski areas occasionally ponied up to seed the clouds, only Vail Associates (now called Vail Resorts) steadily continued funding.
That changed again after 2002, the driest year for streamflows in portions of Colorado since 1685. Everybody from Telluride to Denver was back on the silver-iodide bandwagon again. Among those areas being seeded is the Gunnison Basin, where county government has combined with several water districts and towns to install 28 generators.
The most extensive cloud-seeding program, however, is being done on behalf of the Denver Water Department. Providing not just for Denver itself but also for many of its suburbs, the department relies upon rivers from Hartsel to Dillon to Winter Park. These are all targeted by the city’s new cloud-seeding program, which is being conducted by Durango-based Western Weather Consultants. Larry Hjermstad, another of Lew Grant’s former grad students, is the proprietor.
But, aside from Grant’s work at Climax many years ago, does it work? That was the intent of studies last winter in the upper Blue River drainage. One study suggested that snow packs had been augmented 10 to 15 percent. A second study, conducted at winter’s end, found no traces of silver iodide in the snow pack. The latter may or may not be surprising — a better methodology, say some scientists, is to look for silver iodide in the snow after each storm instead of waiting until season’s end.
This year, with federal money, a more elaborate study is being conducted by scientists from Colorado State University. They are using a randomization technique similar to what Grant used at Climax. By seeding some storms but not others, they seek to predict beforehand how much seeding will increase snowfall in certain areas compared to unseeded areas. The study will then determine if there is any systematic difference between what is predicted and what actually occurs.
This study seeks to determine not only whether weather modification works but also whether the seeding delivery was adequate. If this seeding is successful it will be clear that cloud seeding works and that the delivery was adequate. If it is not successful, it will be difficult to know whether the seeding didn’t work or whether the delivery was inadequate.
“It’s something that has not been attempted very often, if at all, and it’s a very sophisticated model,” says Don Griffith, president of Utah-based North American Weather Consultants, which is seeding the clouds in Gunnison County, among other places.
Conclusions of that study may be important in determining whether Denver continues to fund cloud seeding.
In Utah and the Sierra Nevada, there is a stronger, steadier commitment to winter cloud seeding. Mountains between Cedar City and Nephi have been seeded annually for 30 years. In the Sierra Nevada, near the California-Nevada line, the record goes back even longer. Some watersheds there have been seeded for 50 years on behalf of Nevada, which wants to augment water for farmers and ranchers on the Truckee, Humboldt, and other rivers.
Griffith says cloud seeding should not be considered an antidote to drought. “Cloud seeding should not be viewed as a panacea. It will not solve the drought problem,” he says. “It may help alleviate the drought. It can augment the snow pack 10 to 15 percent. If the natural snowpack is 50 percent of average, it can bring the snow pack up to 60 to 65 percent of average. But it cannot make the drought go away. The best way to see cloud seeding is to see it as a way to help fill reservoirs in good years, to prepare for the drought years.” –A.B.
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