Cloud seeding can increase the water supply in places that don’t have enough. The technology behind it goes back to the 1950s, and scientists are studying how effective it can be in the 21st century.
Jonathan Jennings is a meteorologist who directs the cloud seeding program for the state of Utah. Before that, he worked on cloud seeding in Texas for more than a decade. He recently finished a term as president of the Weather Modification Association.
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Jennings spoke with KUNC about the facts surrounding cloud seeding in the Western U.S. This conversation has been lightly edited for length and clarity.
KUNC: What is the state of cloud seeding in the Colorado River basin and the broader Mountain West?
Jonathan Jennings: Right now, the operational programs in the Mountain West, specifically in the Colorado River Basin, are all winter projects. The goal is to enhance precipitation on the snowpack, which leads to better runoff into the Colorado River. We have active programs in Colorado, Utah and Wyoming.
How much water does cloud seeding add to our mountains?
That is a very challenging question to answer, but through statistical evaluations that have been conducted over the last several decades, we're seeing anywhere from a 5 to 15% increase in additional precipitation. And when you look at the state of Utah as a whole, our evaluations are showing roughly 200,000 acre-feet of additional water into our streams.
That is a lot of water. One acre-foot is roughly the amount of water used by one or two homes each year. Does cloud seeding cause flooding by adding that much water?
Unfortunately, we don't have the capabilities to produce mass amounts of water in short periods of time, so that 200,000 acre-feet of additional precipitation is taking place over the course of a six-month season on a storm to storm basis. Cloud seeding technology today does not have the capabilities to produce flooding in short periods of time.
If we're adding snow that piles up throughout the winter, could it increase the risk of flooding in the spring, if it all melts at once?
If unregulated, yes, that could certainly happen. Fortunately, a lot of the cloud seeding programs across the Mountain West states — and the convective programs in Texas and New Mexico — there's regulatory oversight. Within the bounds of the licenses and permits that these operators have to apply for, suspension criteria exist. So for winter programs, we're always keeping an eye on the percent of normal snow water equivalent, and we have trigger numbers at certain points of the season where if we exceed that number, then we suspend the operations. We don't want to have too much precipitation melt too fast and result in flooding in our rivers.
How is cloud seeding in Texas different from the kind we see in Colorado or Utah? What are the two types of cloud seeding and how are they different?
In Texas, they do their cloud seeding during the warm season, and they're using aircraft with pyrotechnic flares to transport the material into the cloud. In winter programs, they're using ground-based generators to seed clouds that exist over the mountain ranges for the enhancement of the snowpack. The projects in the Mountain West are geared at snowpack enhancement for water supply, whereas a “convective” program like Texas is trying to create additional rain for agricultural use and recharging aquifers.
Cloud seeding uses a substance called silver iodide to cause clouds to drop precipitation. Is that safe for humans and animals?
Cloud seeding is certainly safe. Fortunately, we have the test of time behind us. These projects have been going on in Utah since 1974 and in Texas since 1995. All the testing that has been done in the snowpack and water has shown that the amount of silver that is able to dissolve into water from the silver iodide is minimal, about 0.9 micrograms per liter. The EPA safety level for drinking water is 100 micrograms per liter. Additionally, there's already naturally occurring silver in the environment, and that background level is about six to nine micrograms per liter.
Has cloud seeding ever been linked to human-caused climate change?
No, cloud seeding has never been linked to human-caused climate change. We have to remember that these cloud seeding operations are taking place on the local scale, where we're only enhancing precipitation by 5, 10, maybe 15% and that's just not going to have enough of an impact to cause any climate change at all.
Is cloud seeding causing water to fall in one area by taking it away from somewhere else? In other words, is cloud seeding “robbing Peter to pay Paul?”
You have to look at the amount of moisture that's in a cloud and try to figure out how much is actually precipitating out of that cloud. Data shows that, over the last 20 years, 6 to 9% of all the moisture in a cloud is actually precipitating out. So if we increase that precipitation by 10% now we're at 6.6 to 9.9%. That means we're only tapping into a very limited amount of moisture that's readily available in that cloud. Also, when you go from supercooled liquid water to a water drop or to an ice crystal, that releases latent heat in the cloud. That allows the cloud to grow more robust and allows it to live longer and extend precipitation downwind.
This story is part of ongoing coverage of water in the West produced by KUNC and supported by the Walton Family Foundation.
