SANTA CRUZ, Calif. (KRON) — Mudslides are a major concern for residents living in the 2020 CZU wildfire burn scar and emergency services officials are asking residents to be ready for possible evacuations when the brunt of the storm blows in on Sunday.

A storm system known as an atmospheric river is forecast to dump between 3-5 inches of rain on the Santa Cruz mountains and San Lorenzo Valley Sunday.

If rain falls slow and steady, the ground will be able to absorb water without slides, county spokesman Jason Hoppin said.

Downpours, however, could trigger debris flows.

“If that rain comes down all at once, that could be a problem,” Hoppin said.

“Debris flows are large waves of mud, rocks, trees, and even cars and houses, if it’s big enough. The only way to protect yourself from a debris flow, because they move so fast, is to have moved out of the way before it even starts,” Hoppin said.

Populated areas under the greatest threat of debris flows are eastern-facing mountainsides along the San Lorenzo Valley, Hoppin said.

The National Weather Service Bay Area issued a flash flood watch for the Bay Area Sunday night, “with special emphasis on the 2020 burn areas.”

Roots from trees that usually hold soil in place were burned up by the CZU Fire, leaving the ground prone to slipping down mountainsides.

The Santa Cruz County Office of Emergency Services will issue evacuation warnings and orders similar to how wildfire evacuations are made. Residents are asked to sign up to receive alerts through . OES officials divided the county into hundreds of zones that each have a unique number.

Santa Cruz Regional 911 will also issue alerts through CodeRED reverse 911 calls.

Debris flows can be even more deadly than wildfires, Hoppin said.

The most devastating mudslide in California’s recent history, the 2018 Montecito mudflows, unfolded in a wildfire’s burn scar in Santa Barbara County. Twenty-three people were killed when walls of debris rapidly surged down hillsides and neighborhood streets.

“Some of those bodies have never been found,” Hoppin said.

Santa Cruz mountains and San Lorenzo Valley residents can expect to be alerted by county officials with a warning first, followed by an order, if evacuations are necessary.

“Our geologists have been all throughout the burn scar. They are talking again today about what the threshold should be for evacuations,” Hoppin said.

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