In the end, all it took was a combination of radars and snow gauges.
Scientists at the Boulder-based National Center for Atmospheric Research, the University of Colorado, the University of Wyoming and the University of Illinois at Urbana-Champaign tried a new technique to measure cloud seeding in 2017: They left behind the precipitation gauges and statistical models that have been used in the past.
The end result was a critical research finding: On three occasions, injecting clouds with silver iodide generated significant precipitation, more than doubling the rate of snowfall that had been falling naturally.
“As a scientist, this is kind of what you live for,” said Sarah Tessendorf, a scientist at NCAR and co-author of a new paper about the research “You’re always trying to answer those unanswered questions.”
Scientists flew an airplane that had high-resolution cloud radar that could see features in clouds that are undetectable to the naked eye. Scientists also positioned mobile Doppler radars on wheels that storm chasers use high in the mountains above basins to observe changes in weather.
“Having these mobile radars positioned up on top of mountain ridges to be able to see over the basins where we were targeting cloud seeding, we were able to get measurements that we wouldn’t have seen otherwise,” Tessendorf said.
The results are critical for Western states like Colorado which have seen more frequent and extreme drought. Tessendorf said the next step is potentially even more important: Scientists can figure out what conditions lead to the best cloud seeding opportunities. Then through the use of computer models, she and others can determine how cloud seeding might work in a hotter, drier climate in the west.
“So understanding that we can look at future climate projections and make some assessments about, ‘Is cloud seeding still going to even have the same opportunities … in that future climate?’” she said.
WOLCOTT, Colo. – Each winter, anxious water managers, farmers and city leaders across the Southwest turn their eyes toward the snowy peaks of the southern Rocky Mountains. The piling snow is a massive frozen reservoir, and its depth and weight can foreshadow the year ahead. Millions of dollars are spent divining what a heavy or light snowpack means for the region’s reservoirs, for its booming cities, for its arid farmland.
A lot of the current water scarcity problems in the Southwest could be eased if it just snowed more and more frequently in the high country of Colorado, Utah and Wyoming. More snow means more time to deal with the Colorado River’s fundamental supply-and-demand imbalance.
The onus to correcting that imbalance often falls more on the demand side of the equation, with myriad policy pushes that either incentivize or force people to use less water. On the supply side, options are limited.
There’s one tempting proposition for Western water managers feeling the pressure to dole out cutbacks to users due to the region’s ongoing aridification – inducing clouds to drop more snow.
For decades, states have invested in weather modification programs, also known as cloud seeding, in the hopes of boosting precious snowpack. The practice showed up in a recent agreement among Colorado River Basin states, and investment is expanding, with water agencies in Wyoming and Colorado for the first time putting funds toward aerial cloud seeding rather than solely relying on ground-based generators.
“I can say that we’re up significantly in the last 24 months on the number of smaller large-scale programs that we’re modeling and completing feasibility studies for,” said Neil Brackin, CEO of Weather Modification Inc., a North Dakota cloud-seeding company that operates across the West.
Brackin’s company is in charge of the Colorado and Wyoming aerial programs, flying when moisture-laden snowstorms arrive in northern Colorado’s Never Summer Mountains or southern Wyoming’s Medicine Bow and Sierra Madre ranges.
“Low water and low precipitation over a number of years is creating a lot of interest and demand,” Brackin said. “So we’re excited to be at the table and be part of the solution going forward.”
Despite increasing interest, big gaps remain in our understanding of how well cloud seeding delivers on its promises.
Cloud Seeding 101
Eric Hjermstad huddles around a beige drum about the size of a trash can on a snowy hillside in Colorado’s Vail Valley. It’s filled with a solution of silver iodide — the necessary ingredient for cloud seeding. It’s running low and there’s a snowstorm on the way, hence Hjermstad’s trip from his home base in Durango to fill it up. On top of the drum is a box of valves and a small chimney. A propane tank sits a few paces away.
I told Hjermstad, co-owner of Western Weather Consultants, that I had imagined something more high tech: “Like, is this an old coffee can?”
“This one could be a coffee can,” he replied. “It’s just up on top of the chimney to keep any kind of precip from falling directly into the chimney.”
Hjermstad’s company operates dozens of generators like this one. In theory, these machines send the particles into clouds and force them to drop more snow in desirable locations, such as ski slopes or the headwaters of drought-stricken river systems.
From the site, you can almost see the ski slopes of the nearby Vail and Beaver Creek resorts. This generator works part-time seeding clouds that drop snow for skiing. It also is used to make more snow for water users in the Colorado River Basin, one piece of a broad network of cloud-seeding operations under the purview of the Central Colorado Mountain River Basin Weather Modification Program.
It’s not snowing when we visit the generator, but Hjermstad demonstrates how it works. First, he gets propane flowing and then turns on a valve to the silver solution. With a fire starter, he lights the chimney on top. A bright orange flame flares from the generator, sending microscopic bits of silver iodide into the air.
If there was a stormstorm right now and the wind was blowing the right direction, Hjermstad said, this generator could be influencing how much snow eventually drops.
“We cloud seed to try and pull a little bit more precipitation out of a storm than it would naturally occur,” he said.
A certain class of clouds are particularly ripe for seeding, he said. Some clouds are full of supercooled liquid water, but they’re not dropping that moisture. By injecting small particles into the cloud, a snowflake is able to form. The silver iodide acts as the “seed,” which enables the growth of a new ice crystal. That new snowflake can ricochet through the cloud, amplifying its impact.
“One little ice nuclei out of this could end up creating another hundred, two hundred snowflakes potentially,” Hjermstad said.
From late November to April, Hjermstad keeps an eye on each weather system forecast to drop snow or pass over his generators. If it looks promising, he’ll contact the landowners where the generator sits, tell them when to turn it on and turn it off, and watch its track on radar with ground truthing, courtesy of Colorado’s highway webcams.
For decades, the practice has had a problem with its reputation. Anecdotal accounts from farmers and ski resort owners confirmed cloud-seeding effectiveness. Recent scientific studies have given it more credence, but top experts in the field argue there’s still a lot we don’t know about how well it works.
Science Improves, But Gaps Remain
Picture this: You’re in a small airplane, flying inside a blizzard. The turbulence is intense. You’re sweating because of the stacks of computers on board. There’s no restroom. And you’ll be up in the air for at least four, maybe six hours.
“And then compounded on all of that, you’re watching a little computer screen the entire time,” said Jeff French, an atmospheric science professor at the University of Wyoming.
Could be enough to get most people to lose their lunch, but it’s what French lives for.
“There’s been more than one or two people that have been sick on this plane,” he said.
Parked in a hangar outside Laramie, Wyoming, we’re sitting inside the research plane French uses to study clouds. To get to know a cloud, he said, you need to get inside it. An expensive suite of onboard instruments lets him look at how snow forms in real time.
“Ice crystals come in many many different shapes,” French said. “They can look like six-sided plates. They can look like long needles or columns. They can look like dendrites, which is kind of the typical snowflake shape.”
For years, French has devoted much of his research to understanding the science behind cloud seeding. In 2017, he partnered with the Idaho Power Co. and other researchers to fly his plane behind another plane that was seeding clouds. The result was a series of scientific articles. A 2018 report French co-authored showed for the first time how aerial cloud seeding worked.
“If you put silver iodide into clouds with certain characteristics, you can generate ice. That ice can grow. That ice will eventually fall to the surface as snow,” he said.
The study, called “Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment” (SNOWIE) and conducted in the Payette River basin near Boise, Idaho, was a big deal. Before then, no one had solid evidence showing the physics of cloud seeding in the real world.
With new data in hand, French was able to say, “Yes, the amount of snow that was falling at this location increased.”
That might sound like a definitive endorsement of cloud-seeding effectiveness. But the scientists producing the research are circumspect about their findings, and they caution against taking away too much from SNOWIE’s early results.
“When somebody says, ‘I know that it works,’ I would say, ‘Show me the evidence,’” French said. “Show me the evidence that you know that it works. And I can quantify that.”
Sarah Tessendorf is a researcher at the National Center for Atmospheric Research in Boulder who worked with French on SNOWIE. People ask her frequently whether cloud seeding works. She replies that it depends on how you define “works.” If the question is whether cloud seeding is capable of producing more ice inside a cloud, then the answer is yes. But more often than not, the question is more complicated, and people are hoping for more.
“Sometimes the question … is: ‘Does it produce additional snowpack on the ground?’ And we’re still working to try to answer that question,” Tessendorf said.
She’s cautious about what she can prove when it comes to cloud seeding. In the past, studies have shown the practice could boost snowpack by as much as 15 percent. Tessendorf said the increase in snowpack cited in those studies has been a moving target over the years, with varying levels of rigorous data gathering. When she and other researchers want solid proof, they’re looking for a 95 percent level of confidence that cloud seeding caused the increase, rather than a serendipitous series of storms.
“There’s still enough chance that (the increase) could have been a random effect,” Tessendorf said. “From a scientific perspective, we haven’t been fully convinced.”
There are plenty of other caveats from the study. In SNOWIE, planes sprayed silver iodide into more than two dozen clouds that looked ripe for seeding. But they could only draw a clear link between seeding and snowfall in three cases. There’s a small signal cloud seeding created additional ice in a handful of others. And then no signal in at least 20 cases.
Figuring out which clouds will respond to seeding and which won’t remains an open question. Plus, she said, the study was limited based on geography, only seeding clouds in southern Idaho, which undoubtedly are different from clouds in other parts of the West.
“It’s a complicated problem and the results that we see in one cloud will not automatically apply to every cloud everywhere,” Tessendorf said.
But those scientific blind spots haven’t stopped states and water agencies from investing in the technology. French, at the University of Wyoming, said water leaders should know gaps remain in our understanding of how well cloud seeding works.
“The evidence is pointing into the direction, that it does have an impact and we can increase snowpack,” he said. “But I’m skeptical still when I hear people say 10 to 15 percent because that number to me is something that is difficult to justify.
“They should realize that there is a risk associated with it, and that risk is that it may not be having an impact at all.”
Still, given the shortages within the Colorado River Basin, he’s not surprised that some see the practice as worthwhile and are willing to front the cost to make it happen.
Water Managers Place Their Bets
In a gilded Las Vegas conference room in December 2017, water managers detailed their solutions to the Colorado River Basin’s chronic water scarcity, and how to wean the Southwest from total reliance on the overtaxed river.
A representative from the Upper Colorado River Commission laid out what Colorado, Wyoming, New Mexico and Utah would bring to the table. A three-pronged Drought Contingency Plan included a focus on demand management, which would create a dedicated pool of saved water within Lake Powell. Another prong dealt with reservoir operations to streamline decision-making between state and federal agencies. The third was a recommitment to weather modification programs that had been in place in some form since 2007.
In mid-2018, before wrangling over Colorado River Drought Contingency Plans reached a fever pitch in the river’s Lower Basin, water agencies in California, Arizona and Nevada agreed to spend upward of $1.5 million each year on cloud-seeding programs in the watershed’s upper reaches.
“The reason that cloud seeding is being implemented on a relatively large scale in the Colorado River Basin is it’s a very low-risk, high-reward scenario,” said Dave Kanzer, an engineer with the Colorado River District and manager of the Central Colorado Mountain River Basin Weather Modification Program, which receives funds from Lower Basin water agencies.
If you’re a water manager in the Southwest, it’s easy to think of cloud seeding like an extra battery for a smartphone. The guy selling the battery tells you it will probably only charge your phone another 4 or 5 percent, maybe more if you plug it in at exactly the right time. So it’s not reliable, but it’s the cheapest on the market. Every other battery is expensive and takes years to make. And if a lot of people are counting on you to make a call, you might just be willing to buy the battery, even if it ends up doing nothing in the end.
Kanzer said investors understand the risks involved and aren’t under a delusion that it will be the basin’s saving grace.
“It’s sort of a common sense look at the issue where we are imbalanced between water supply and water demand,” Kanzer said. “We can change water demand by changing habits by conserving, by increasing efficiencies. When you look at supplies, what can we do? There’s very few options.”
Colby Pellegrino, with the Southern Nevada Water Authority, the water utility for Las Vegas, said her agency’s investment in Upper Basin cloud seeding is worthwhile.
“Most of the information out there says yes, some water is gained through weather modification,” she said. “The amount of water that’s gained is pretty inexpensive water compared to the other options that are out there.”
Concerns Reach Beyond Effectiveness
Even though cloud seeding has occurred over the basin for more than a decade, not everyone is on board.
“You read one side of the story and yes, it’s really working,” said Patti Clapper, commissioner in Colorado’s Pitkin County. “You read the other side and we really don’t know.”
Discussions are occurring in her county now about expanding a cloud-seeding program and using tax dollars to pay for it. She has lots of unanswered questions about the long-term effects of spewing silver iodide into the air, and broader philosophical concerns about forcing snow to drop in one place at the possible expense of somewhere else.
“The data’s not there,” she said. “Yes, we need to be concerned about the water in our rivers because of the drought, because of climate change. But you have to be careful when you mess with Mother Nature because she can bite you in the butt.”
Katja Friedrich, an atmospheric science professor at the University of Colorado-Boulder, hears such concerns often.
“This is a really big stretch to say we are stealing water vapor,” she said, adding that clouds and weather systems are incredibly dynamic.
And, given how difficult it is to measure the effectiveness of cloud seeding in a very specific target area, it’s even more difficult to quantify any effect further downwind, she said. Even if cloud seeding were wildly successful — say it was able to produce 15 percent more snow — it’s likely that any downwind effect would be minimal as clouds are constantly changing, recharging with new sources of moisture as they move through the atmosphere.
“This is a good question that we should not just throw off the table,” Friedrich said. “But it’s very difficult to quantify.”
The public should be questioning state leaders who invest in cloud seeding programs, she said, and demand stronger monitoring of stream health and proof of effectiveness. But at the same time, she knows why agencies are increasingly interested in the process.
“The general public has to understand that we are in a water crisis,” she said. “So we need to ask the question, what kind of luxury do we have? Do we want to have a shower every day? That comes at a price. If we don’t want to have cloud seeding, then we need to reduce our water demand.”
This story is part of a project covering the Colorado River, produced by KUNC and supported through a Walton Family Foundation grant. KUNC is solely responsible for its editorial content.