Cloud seeding not connected to California storms

Heavy rain pounded much of California beginning Feb. 18, leaving about 37 million people across the state under flood alerts at one point, according to news reports.

Some social media users baselessly tied the wet weather to a pilot cloud seeding program — a type of weather modification — that’s intended to increase precipitation and thus, the state’s water supply.

A Feb. 19 Instagram post shared a video with sticker text that read, "The rain in California."

"California, check this out. This may be the reason your weather is off lately," a man in the video said.

The video shows a woman speaking at a public meeting about a Santa Ana Watershed Project Authority cloud seeding program. She said there could be unintended consequences of cloud seeding, such as an increase in urban flooding and said the silver iodide used in the process is toxic.

The original video received more than 2 million views on TikTok. We found other social media posts making similar connections between the storms and the cloud seeding program.

This Instagram post was flagged as part of Meta’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Meta, which owns Facebook and Instagram.)

The Watershed Project Authority launched a four-year cloud seeding pilot program in November that will target four mountain areas in Southern California chosen for their contribution to seasonal runoff. Its goal is to increase the water supply in the Santa Ana River watershed, the region’s largest river basin. Cloud seeding works by releasing silver iodide particles into the clouds during storms to increase precipitation.

But the Instagram post misleads both about the cloud seeding program’s  connection to recent storms and silver iodide’s safety.

A storm fueled by an atmospheric river — narrow corridors packed with water vapor that the National Oceanic and Atmospheric Administration calls "rivers in the sky" — dumped buckets of rain, heavy winds and snow across California for three days beginning Feb. 18. In early February, similar back-to-back storms pummeled California, the second of which triggered hundreds of landslides in Los Angeles and killed at least nine people.

However, no cloud seeding took place during the two most recent severe storms, said Santa Ana Watershed Project Authority spokesperson Melissa Bustamonte.

"Cloud seeding was not performed during the Feb 3-8 storm events. These storm events were determined to be either too large or too close in succession to cloud seed," Bustamonte said. "Also, the storm event of Feb 18-19 was not seeded either."

The authority’s website lists the dates and areas where cloud seeding took place. The last cloud seeding happened Feb. 1, the website shows. Southern California that day was drenched by a storm dubbed a "Pineapple Express" — meaning an atmospheric river originating from Hawaii.

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"During the February 1 storm event, cloud seeding operations occurred in target areas within the San Gabriel Mountains, San Bernardino Mountains, and San Jacinto Mountains to increase snowpack," Bustamonte said in an email.

The pilot program targets four mountainous areas surrounding the watershed in Orange, Riverside and San Bernardino counties to enhance snowpack at those high elevations during storms, Bustamonte said.

The program does not seed areas in Los Angeles, Ventura or San Diego counties, she said.

The pilot program has "suspension criteria," safeguards that prevent cloud seeding when there are potentially hazardous weather conditions, according to a report produced for the Watershed Authority in 2020.

"The objective of suspension is to eliminate the real and/or perceived impact of weather modification when any increase in precipitation has the potential of creating or contributing to a significant flood hazard," the report said. 

Experts told PolitiFact the recent storms have no connection to the cloud seeding program, and that the silver iodide used in the process is considered safe.

"You only have to look at a satellite image to see where the rain is coming from," said Gudrun Magnusdottir, a University of California, Irvine earth system science professor. She pointed to massive weather systems that have associated atmospheric rivers.

"No attempts at cloud seeding in some mountain region would cause such widespread precipitation as we are witnessing all over California," Magnusdottir said.

Adele Igel, an associate professor in the University of California, Davis’ Department of Land, Air and Water Resources, said cloud seeding does not change general weather patterns.

She said estimates from the Santa Ana Watershed Project Authority feasibility study show that ground-based seeding could increase precipitation by up to 4.5%.

"This means that if an area would have received one inch of precipitation without seeding, it would instead receive 1.045 inches with cloud seeding," Igel said. "The cloud seeding then is not the determining factor for heavy rain."

Igel also said the silver iodide used in the cloud seeding "is harmless to the environment."

A pilot program fact sheet said more than 50 years of research has shown no "measurable human or environmental effects resulting from the use of silver iodide." The concentration of silver iodide in water or snow from a seeded cloud "is nearly 1,000 times less than the Environmental Protection Agency standards," the fact sheet said.

An Instagram post connected recent California storms and flooding to a pilot cloud seeding program underway in the state.

But the cloud seeding didn’t take place during the two most recent storms, and experts said it couldn’t cause the storms and heavy rainfall seen across the state. The claim is False.