Eight States Are Seeding Clouds to Overcome Megadrought — Scientific American

Graphic credit: “Literature Review and Scientific Synthesis on the Efficacy of Winter Orographic Cloud Seeding” — CIRES

From E&E News (Chelsea Harvey) via Scientific American:

Interest in cloud seeding is growing as temperatures steadily rise, increasing drought risks in places like the Mountain West. But there’s a catch. Scientists aren’t sure how well cloud seeding works today, let alone in a warmer climate.

Amid growing concerns about water resources in the western U.S., scientists are working to answer those questions. Today, cloud seeding research represents the cutting edge of weather and climate science—a convergence of questions about the influence of warming on our dwindling water resources and our ability to control those consequences.

“Certainly we’re in a better position now to address that question than we were 10 years ago,” said Jeff French, an atmospheric scientist at the University of Wyoming. “The state of the science has progressed to the point that it is a question that we can and should be trying to address now.”

Cloud seeding can take a few different forms. In some places, it’s used to boost rainfall or prevent hailstorms. But in the U.S., it most commonly aims to enhance snowfall, and usually with silver iodide.

Extra snow can be a boon for water resources, especially in places like the drought-plagued West…

Boosting snowpack is being pursued with growing urgency. Much of the western U.S. has been gripped by drought for the last 20 years…

Weather experiments are notoriously difficult to conduct. The scientific gold standard would be a study that proves cloud seeding produced an outcome that definitely would not have happened without it. But that kind of research requires a combination of specialized experimental design and highly advanced technology.

For most of cloud seeding’s long history, it just wasn’t possible. Only within the last few years has technology advanced enough for researchers to really dig into the problem…

Today, cloud seeding operations take place in at least eight states across the western U.S., with varying levels of investment often shared among state agencies, utilities and private companies such as mountain resorts.

Cloud seeding programs in the upper Colorado River Basin, for instance, cost around $1.5 million each year. The costs are split among state agencies in Colorado, Utah and Wyoming, where the majority of the operations take place, as well as Nevada, California, New Mexico and Arizona, which also stand to benefit from increased flow on the Colorado River.

In the last few years, cloud seeding has featured more prominently in drought management strategies across the West. The cost-sharing agreement in the Colorado River Basin was finalized in 2018, after states had spent years individually managing their cloud seeding operations. The agreement extends through the fall of 2026.

Since 2018, Wyoming and Colorado have strengthened their programs by investing in aerial cloud seeding operations—that’s seeding conducted by aircraft—in addition to the ground-based machines they already have scattered throughout the mountains.

These are relatively inexpensive investments, all things considered—a low risk for a potentially high reward. But is it actually making a difference?

Most programs point to statistical studies to justify their efforts. These studies indicate that seeded clouds can produce around 5% to 15% more snowfall compared with areas where no cloud seeding took place.
If that’s right, it puts the cost of cloud seeding at around a few dollars per acre-foot of water (equivalent to about half an Olympic-size swimming pool). That’s far less expensive than the cost of many other water-saving interventions, such as water conservation, recycling or desalination, which can cost hundreds of dollars per acre-foot.

Still, statistical studies don’t prove that cloud seeding is actually causing the heavier snowfall. That requires a more specialized scientific experiment—and only within the last few years have scientists finally been able to make that happen.

As recently as 2015, an extensive report prepared for the Bureau of Reclamation concluded that continued research is still warranted, but it noted that “the ‘proof’ the scientific community has been seeking for many decades is still not in hand.”

[…]

On Jan. 19, 2017, a research plane roared through the gray skies above Idaho’s Payette River Basin, spewing silver iodide into the air. Assembled on the snow-capped peaks below, snow gauges and portable radar machines were poised to measure the snow that scientists hoped would follow.

It was the beginning of an experiment that would turn cloud seeding science on its head. Known as the SNOWIE project—short for “Seeded and Natural Orographic Wintertime Clouds”—the study provided some of the first quantitative evidence that cloud seeding actually works.

For three days that January, weather conditions would align to set up the perfect cloud seeding experiment. The sky was cold and cloudy—but no snow was falling. Over the course of these three days, the research plane would make more than a dozen trips over the mountaintops, releasing the same amount of silver iodide each time.

“For three days there was cloud cover, but no snowfall, no natural precipitation,” said Katja Friedrich, an atmospheric scientist at the University of Colorado, Boulder, who helped lead the SNOWIE project. “We put the seeding material into the supercooled liquid cloud, and we were able to generate precipitation. And that was very revolutionary.”

Thanks to high-tech radar equipment, the scientists were able to monitor the response of the clouds from the moment the silver iodide was released into the air until the moment snow began to fall. Over the course of those three days, the scientists estimated that around 286 Olympic swimming pools’ worth of snow fell from the clouds they seeded.

Friedrich and her colleagues, including scientists from Colorado, Wyoming, Illinois and Idaho, published their findings in a groundbreaking paper last year in Proceedings of the National Academy of Sciences.

SNOWIE came in the midst of a kind of a renaissance for cloud seeding research in the United States. After years of relatively little scientific interest in weather modification, a series of projects over the last decade have paved the way for new insights.

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