St. Vrain watershed will pilot cloud seeding on Front Range

As the precarious future of water supply looms over Colorado’s Front Range, one surprising solution on the St. Vrain watershed might be to simply make more water.

The St. Vrain watershed will be piloting a cloud seeding project this winter, the first of its kind on the Front Range, to see how infusing silver iodide into the clouds might improve winter snowpack.

While cloud seeding has taken place on the Western Slope since the 1950s, the pilot project led by the St. Vrain and Left Hand Water Conservancy District, or SVLHWCD, will be the first project in the state along the urban corridor.

North American Weather Consultants is the contractor that will be responsible for the cloud seeding. President Garrett Cammans explained that his company goes back to the early 1960s when they started researching weather modification in California.

“Cloud seeding is actually very simple in nature once you understand the mechanisms behind it,” Cammans said. “Storm systems are actually very inefficient at creating precipitation. Ninety percent of the moisture inside of a typical storm system will remain in the air and will not fall to the ground as precipitation.”

In order for moisture to fall out of a cloud, it needs to freeze and form a snowflake large enough that it can fall past the upward drafts in the sky. Cloud seeding introduces microscopic particles in the form of silver iodine into the cloud deck that instigate the freezing process, turning liquid water into snowflakes faster.

This means that cloud seeding cannot create storm systems; an existing cloud is needed for seeding to work. The seeding takes place in consecutive storms throughout the season, typically about 15-20, which could increase the snowpack of the watershed by 5-10% or thousands of additional acre feet of water during the spring runoff.

The per acre-foot cost of additional water is usually between $5-20 in most Colorado and Utah projects, Cammans said. SVLHWCD Executive Director Sean Cronin and Water Resources Engineer Scott Griebling said the project this winter will cost $140,000 in total.

“That’s one of the most appealing aspects of this is, especially compared to the cost of buying water or even renting water on a cost per acre foot basis, this is one of the cheapest ways of increasing the water that’s available to use,” Griebling said.

SVLHWCD is not a water user, so they won’t directly benefit from the effort they are leading and financing with taxpayer dollars, but their constituents will likely all benefit regardless of how they use water.

Cronin said the idea of cloud seeding the St. Vrain watershed came about in 2019 when they began identifying approaches to manage and develop water. Water entities historically increase supply by buying it from someone else, essentially moving the same amount of resources between different users, Cronin explained.

“Colorado’s water plan really highlighted that that is something that could be problematic for the entirety of Colorado and the South Platte Basin,” he said. “One of the drivers and ideas behind St. Vrain and Left Hand Water Conservancy District’s water plan is, how can we provide water supplies that provide mutual benefits for all uses and not create winners and losers?”

That’s when the conservation district started looking at the science of cloud seeding, not wanting to create any unintended consequences or issues. They were eventually satisfied that this was something worth exploring at the pilot scale.

The Colorado Water Conservation Board is co-sponsoring the project by taking on the capital costs, roughly $80,000-$90,000. The Left Hand Ditch Company will also be paying a portion of the operational costs with SVLHWCD, and the Highland Ditch Company will be contributing in kind support by allowing one of the two cloud seeding generators to be built on their property.

These generators, located at the base of the foothills, will shoot the silver iodine into the atmosphere to be carried up into the clouds as a snowstorm is forming.

Griebling pointed out that much of the water on the east slope comes from the West Slope through transmountain diversions, meaning many residents and agricultural producers on the Front Range are using Colorado River water. 

“As the megadrought and persistent aridification in the Colorado Basin has occurred and continues to occur, the availability of that supply is likely to diminish, so this is a great way of us shoring up our local water supply and doing what we can to alleviate our need for additional Colorado River supplies,” he said.

At build out, Longmont’s water managers plan to have one-third of its water supply from West Slope sources and two-thirds from its native basin, the St. Vrain.

While the SVLHWCD has seen mostly support for the pilot project, there have been concerns about cloud seeding’s impacts on the environment since it started being used decades ago.

Gammans said his company adheres to strict environmental protection practices and only a small amount of silver iodine is released for cloud seeding — he estimated it would be about two pounds of seeding agent for the St. Vrain watershed over the entire season.

“We’re introducing molecules that are naturally existing, naturally occurring elements into the cloud and all it’s doing is making the process of converting liquid to a solid more efficient in the cloud,” Gammans said.

Another long standing worry is whether cloud seeding takes moisture away from other areas that would have otherwise gotten it. The American Meteorological Society said in 2010 that the unintended consequences of cloud seeding have not been clearly demonstrated, but can’t be ruled out.

A 2014 assessment of the effects of cloud seeding outside the intended area found that it may actually help increase precipitation in surrounding areas, though it called for further research.

Gammans argues that the impact is small compared to the overall water system. He pointed out that in a storm, which typically drops about 10% of its moisture, cloud seeding increases productivity by 5-10%.

“So 10% of 10% is only 1%, and that means that instead of dropping 10% of its moisture, it’s going to drop 11% of its moisture,” he said. “There’s still 89% of that storm’s moisture that’s moving on to the next watershed. So it’s very insignificant in the grand scale of things that we’re pulling out.”

Cronin added that the data on the St. Vrain pilot project  will be reviewed as it comes in this winter and beyond. If the project is successful, he said there will likely be an appetite to add more stations locally.