Water & Drought

Desperate for new water supplies, SLO County bets on cloud-seeding program

It was the summer of 2015, and San Luis Obispo County was in the fourth year of severe drought with no rain in sight.

Half-empty reservoirs were declining, the water table was noticeably dropping, farmers had fallowed fields. Water managers responsible for city and agricultural supplies frantically looked for possible emergency water sources if conditions got worse.

Brian Talley, third-generation farmer and president of Talley Fields and Talley Vineyards in Arroyo Grande, made the tough call to plant fewer crops in the fields around Huasna Road after the wells used to irrigate the farm and vineyard “became very unproductive.”

“As Lopez Lake continued to drop, we were concerned they may have to shut off the flow to Arroyo Grande Creek, which would reduce or eliminate the recharge of our aquifer. Fortunately, that did not happen,” Talley told The Tribune in a recent phone conversation.

That experience was likely on his mind Tuesday when he stood before the county Board of Supervisors and urged the implementation of a weather modification program that could, maybe, in the right conditions, increase the flow of water into Lopez Reservoir by 5,500 acre-feet a year.

“I support cloud seeding because we need more water,” Talley told the board. “It’s cheaper than any other way to increase our water supply.”

Board members unanimously agreed and approved a weather modification program for the Lopez Lake watershed. With $300,000 already set aside by Zone 3 of the San Luis Obispo County Flood and Control Water Conservation District, cloud-seeding airplanes could fly over the reservoir as soon as January.

What is cloud seeding? An experiment

Cloud seeding has been used around the world and in parts of California for decades to increase rain or snowfall during storm events. Water managers are convinced they see results, although there is no scientific consensus on its efficacy.

Here’s how it works: Particles are released into clouds from either ground flares on hilltops or dropped by an airplane. Water droplets attach to the particles, creating mass, and the heavier frozen particles fall toward the ground as rain or snow.

Generally, the material used is silver iodide because the compound has a similar molecular structure of an ice crystal. So, basically, they shoot silver into the sky from cannons to make it rain. Kind of.

cloud seeding.JPG
How cloud seeding works. County of San Luis Obispo Public Works Department

The process doesn’t make rain out of thin air. Rather, it is supposed to “augment rainfall and runoff in watersheds,” as described by the Santa Barbara County’s Public Works Department, which has operated a cloud-seeding program since 1981.

“Sometimes, there are predictions of an inch of rain and nothing happens,” said Ray Dienzo, an engineer with the water resources department of county Public Works. “The idea of cloud seeding is, it would take those opportunities and make some rain of it.”

It could increase rainfall of each storm event this winter by between 9 and 17 percent, according to estimations provided in a 2017 feasibility study based on local cloud-seeding studies performed by Santa Barbara County in the 1990s.

The idea of the government conducting routine weather modification might sound a little sci-fi, and it is certainly fodder to feed conspiracy theories. But Dienzo thinks it will work.

“I’m an engineer, so I’m curious to try different technology, especially in the realm of weather augmentation,” he continued. “I think there’s been enough science to prove it. I believe it will work.”

There are some reasonable concerns.

flare dispersing silver iodide.JPG
Flares at ground sites are used to distribute silver iodide at high elevations to attract water droplets in storm clouds. County of San Luis Obispo Public Works Department

Critics are wary of bio-accumulation of silver iodide, for example. Officials point to a brief environmental review that says the compounds have “a rather low order of toxicity,” and that accumulations in soil, vegetation and surface runoff “have not been large enough to measure above natural background levels.”

Then there’s the issue of modifying the weather. Given that there is a definitive amount of water on Earth and in its atmosphere, it seem logical to wonder if manipulating water droplets to fall in one place would result in fewer water droplets falling elsewhere.

To that, the answer is basically that storm systems are complicated. There’s not strong evidence that nearby areas would see any decrease in rainfall. Instead, they might see a slight increase.

Still, some say the program distracts from what the focus should be: conservation.

“Rather than potentially throwing money away on an unproven technology, the county should fund efforts that we know will work, such as increasing conservation,” Cynthia Replogle, of Oceano wrote to the county.

Racing for water before drought returns to Arroyo Grande

It’s not the only program local agencies are banking on to increase water stability, but it is one of the quickest and the cheapest.

“In the Lopez area, it’s very important. We were the first to go into the drought and the last to get out of it,” Supervisor Lynn Compton said at Tuesday’s board meeting.

“There are many different solutions and projects that people are looking at to bring water in,” she continued. “This is just one of the tools in the tool box.”

In the time since the drought officially ended, nearly all the reservoirs in the region have refilled except Lopez.

Unlike other reservoirs in the county at 75 to 99 percent capacity, Lopez Lake is currently about 60 percent full.

Thousands of people rely on the watershed for their drinking and irrigation water — including in Pismo Beach, Arroyo Grande, Grover Beach and Oceano. In addition, groundwater there sources irrigation for thousands of acres of prime farm land, and fresh water in Arroyo Grande Creek is essential for habitat protection for species like steelhead.

In the midst of the drought, the reservoir dropped below 20 percent full, and municipalities had to cut use. Scrambling for a solution as the situation worsened, some people on the Zone 3 advisory committee recalled the studies Santa Barbara County did in the area two decades earlier.

“We didn’t see any rain on the horizon, no sign that rain was even going to come. There was talk that the whole Arroyo Grande area was going to run out of water in three years. The talk was: We need to do something,” Dienzo said.

The cloud-seeding program aims to increase rainfall into Lopez Lake, which saw lake levels fall precipitously during the drought, as seen here in 2016. David Middlecamp dmiddlecamp@thetribunenews.com

That’s when cloud seeding was reintroduced as a viable option.

They ranked potential emergency water supply options with an initial evaluation based on cost, time to implement, and average supply of benefit. They discussed supplies from the State Water Project and water market purchases.

Cloud seeding was near the top of the list, with enhanced conservation and land fallowing in the No. 1 and 2 spots.

The ideas of conservation and irrigating less land fell from the collective priority when heavy rains returned. By 2018, Zone 3 consumed more water than it had historically, according to advisory meeting notes.

Other options, like desalination and water recycling are far on the horizon. They cost millions of dollars in infrastructure and time to work through permit approvals, design and building. And the cost per acre-foot is estimated to be between $1,000 and $2,000, according to Talley.

Those are still viable in the long run. The Central Coast Blue project aims to increase the area’s available water supply by 30 percent with recycled water. And there’s talk of using the desalination plant attached to the soon-to-be-closed Diablo Canyon nuclear power plant. That’s years in the future, and requires a long pipeline.

Meanwhile, cloud seeding — with an estimated cost of less than $150 an acre-foot — is enticing.

Plus, Dienzo said, if it doesn’t work, they’ll just stop doing it.

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Monica Vaughan reports on health, Cal Poly, San Luis Obispo County, oil and wildlife at The Tribune. She previously covered crime and justice in the Sacramento Valley, is a graduate of the University of Oregon journalism school and is a sixth-generation Californian. Have an idea for a story? Email: mvaughan@thetribunenews.com