New rules for Colorado’s cloud-seeding program

‘Target and control’ studies to evaluate effectiveness of snowfall enhancement efforts

Can humans enhance one of nature's finest products? Bob Berwyn photo.
Can humans enhance one of nature’s finest products? Bob Berwyn photo.
A ground-based silver-iodide generator in Colorado. Photo courtesy CWCB.

By Bob Berwyn

FRISCO — Colorado’s $1 million cloud-seeding program continues to expand, and under new rules adopted this past summer, the state and the water providers and ski areas who pay for the program hope to get a better idea if their efforts to boost snowfall are effective.

As part of the state-authorized weather modification plan, operators of cloud-seeding operations are required to complete annual “target versus control” analyses, comparing snowfall in target areas against similar non-targeted control areas. Over time, the data from those evaluations may help determine if cloud seeding really does boost snowfall by up to 15 percent, as claimed by the operators.

“This method is credible and develops relationships between snow data and tracks precipitation totals over time in both seeded areas and non-seeded areas to help track the efficacy of the program,” said Maria Pastore, of Glenwood Springs-based Grand River Consulting, who manages the central mountains cloud-seeding rogram.

“In addition, the State has new data types and evaluation methods suggested for cloud seeding programs,” Pastore said. “They are not required but are suggested as good periodic evaluations that can help the long-term sustainability of these programs.”

Cloud seeding in Colorado involves burning silver iodide in ground-based generators to inject tiny particles of the material into approaching weather systems. The silver iodide is said to provide nucleii for crystal formation and growth, helping to wring a bit of additional moisture from the clouds.

For the 2012-2013 season, the central mountains program will cost $293,600 and target an area of about 1,668 square miles of the Upper Colorado River Basin, generally above elevation 8,500 feet, in parts of Pitkin, Eagle, Summit, and Grand counties. If it works, the program could benefit A-Basin, Breckenridge, Keystone and Winter Park, all included in the target area.

Pastore said there are 16 manual generators, 2 remotes, plus 11 co-shared with the Vail program (same number as last year), however not all are operational at the same time during a seeding event.

Generally, cloud-seeding in Colorado begins during November snowstorms, but this year the program is off to a tough start, with only one seeding opportunity in November — the lowest ever —according to Larry Hjermstad, of Durango-based Western Weather Consultants, who runs the seeding operations that cover the central Colorado mountains.

Are there negative impacts?

Over the years, some communities downstream of seeded areas have complained that the operations “steal” moisture, but there is no evidence that the process depletes moisture to the point that it affects precipitation in outside the target area — on the other hand, there is no evidence that it doesn’t either.

To date, there are few environmental concerns about the impacts of adding silver iodide to the atmosphere. Again, there’s very little, if any, evidence that the material accumulates in any measurable amounts on the ground or in the water. Several years ago, Denver Water examined targeted areas for traces of silver iodide as a way to try and confirm the effectiveness of seeding, but no traces of silver iodide were found in the snow.

A 1995 environmental study in California found that, so far, accumulations in the soil, vegetation, and surface runoff have not been large enough to measure above natural background. In 2004, an expert panel in Australia confirmed those results.

It’s not clear exactly how much additional snow and water the cloud seeding will yield, although past data suggests a 10 to 15 percent boost.

“A number is difficult to quantify as it depends on the weather (seedable storms) and effectiveness of the program, which varies year to year,” Pastore said.

The funding comes from the Front Range Water Council including Aurora Water, Denver Water, Colorado Springs Utilities, Northern Colorado Water Conservancy District, Twin Lakes Reservoir & Canal Company, Southeastern Colorado Water Conservancy District, and Pueblo Board of Water Works. The Colorado River Water Conservation District, A-Basin, Keystone, Breckenridge, and Winter Park also participate.

“Although not a participant, additional funding will be provided from the Colorado Water Conservation Board and the Lower Basin States which includes Southern Nevada Water Authority, Central Arizona Water Conservation District, and California Six Agency Committee,” Pastore said.


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