Whenever there is a large storm within the American West, pilots are seemingly flying into the attention, seeding clouds with a substance referred to as silver iodide. The purpose is to extend precipitation.
Cloud seeding has been round for the reason that Nineteen Forties. It’s change into widespread of late because the West battles a drought of historic proportions. States, utility firms and even ski resorts are footing the invoice.
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While it was was assumed for many years to be efficient, current research have helped show that cloud seeding works, and there is no proof that silver iodide is dangerous at present ranges. Experts say cloud seeding usually yields a 5% to fifteen% enhance in precipitation.
It’s no remedy for drought, however cloud seeding will be an necessary water administration device.
“We can’t make a storm happen and we can’t create conditions in this storm that are ideal. Those happen naturally,” stated Jason Carkeet, a utility analyst and hydrologist with the Turlock Irrigation District in central California. Turlock began its cloud-seeding program in 1990.
“What we’re doing is just taking advantage of existing conditions, naturally occurring conditions, and trying to make the storm again more efficient from a water supply perspective,” Carkeet stated.
How cloud seeding works
When carried out aerially, cloud seeding entails loading up a aircraft with silver iodide. Flares are positioned on the wings and fuselage.
The pilot reaches a sure altitude, the place temperatures are superb, and shoots the flares into the cloud. The silver iodide causes particular person water droplets throughout the clouds to freeze collectively, forming snowflakes that finally change into so heavy that they fall.
Absent the freezing course of, the droplets would not bond collectively and change into giant sufficient to precipitate as both rain or snow.
“The cloud initially is all water,” stated Bruce Boe, vice chairman of meteorology at Weather Modification International, a personal firm that is been offering cloud-seeding companies since 1961. “Eventually, as it gets toward the summit of the mountain, it may be 50% ice or maybe more than that. But even if it is, there’s still a lot of liquid water left there.”
Boe stated there is a “window of opportunity” to get the precipitation large enough to fall “before it crests the mountain and starts to descend and thus warm.”
Pilot Joel Zimmer, who works for Weather Modification International, affixes silver iodide flares to the underside of a cloud seeding aircraft.
Katie Brigham | CNBC
For cloud-seeding pilots like Joel Zimmer, who works with Weather Modification International to seed clouds for the Turlock Irrigation District, flying into the storm will be an exhilarating however intense expertise.
“By the time the wheels are up, you’re in cloud,” stated Zimmer, whose route entails seeding over the Sierra Nevada mountains. “And we’re in cloud the entire mission until we’re shooting an approach back into an airport and then pop out of the clouds and have a visual on the runway. It feels like you’re a sub commander in the Navy. You don’t see anything.”
From a water provide perspective, it is most beneficial to seed clouds over mountains, the place the water is actually saved as snow till the spring runoff.
“When it’s out on the plains such as North Dakota, it’s still a benefit because it helps recharge soil moisture,” Boe stated. “But it can’t be stored and used for a later date.”
While Texas makes use of cloud seeding to assist irrigate fields for farmers, it is extra widespread within the West, the place states like Idaho, California, Colorado, Utah and Wyoming use it to assist replenish their rivers and reservoirs. Most packages use planes for cloud seeding, however some use ground-based flares.
“It’s a lot more common than people think,” Carkeet stated. “More basins have a seeding program than do not have a seeding program.”
Costs and influence
Boe says the associated fee is nearly all the time price it.
“It makes a lot of sense to water managers to go ahead and do it, even if the increase is on the order of a few percentage points,” he stated.
Idaho Power spends about $4 million a yr on its cloud-seeding program, which yields an 11% or 12% enhance in snowpack in some areas, leading to billions of gallons of further water at a price of about $3.50 per acre-foot. That compares with about $20 per acre-foot for different strategies of accessing water, corresponding to by way of a water provide financial institution.
And although Turlock solely sees a 3% to five% enhance in runoff from its program — which has a most finances of $475,000 — California will take all the additional water it may well get.
“It’s one of the things that makes it so hard to evaluate, is you don’t see a doubling or tripling of the precipitation,” Boe stated. “You see an incremental increase, but you add that up over the course of a winter and then it can be significant.”
Watch the video to be taught extra about what it takes to make it rain.