After the Thomas wildfire scarred hillsides in the Santa Barbara County community of Montecito, rainstorms triggered debris flows that killed 23 people, injured 167 and damaged more than 400 homes. On average, 25 to 50 people are killed by landslides - including debris flows and rock falls - every year in the United States, according to the U.S. “We don’t want to inappropriately raise the thresholds and then have a debris flow occur in the absence of an evacuation and have people get hurt or killed.” “We’re trying to err on the side of caution to protect public safety,” Strudley said. It’s not clear if debris flows occurred in those areas, according to Strudley, which included some remote regions of Bonny Doon, Davenport and Swanton. Those thresholds were also met during a rainstorm that impacted some areas of Santa Cruz County Thursday night and early Friday morning. “We didn’t have any catastrophic debris flows but we did have some small ones.” “What we saw this last year was that the thresholds were meaningful,” Strudley said. Scientists still need more data to determine if debris flow risk thresholds should be raised, said Mark Strudley, Santa Cruz County Flood Control Division manager. Some nine months ago, a January storm triggered evacuations for thousands living near CZU Complex burn scars in the Santa Cruz Mountains, but did not result in damaging debris flows or floods. Officials are cautioning residents to drive carefully, and secure objects on high profile vehicles. Gusty winds could reach speeds up to 45 mph in the Santa Cruz Mountains on Sunday. “It’s not how much rain, or how big the drops are, it’s just how quickly it’s coming.” “If you slowly pour out a gallon of water, you can kind of let that water fizzle out, but if just drop it and it all comes at once, it’s going to be a mess,” explained National Weather Service meteorologist David King. The risk the storms pose to triggering debris flows and floods largely depends on how fast the rain falls to the ground. They’re rated on a system of 1 to 5: Sunday’s is currently at category 5. “Atmospheric river” storms can produce large amounts of rainfall, and drop that moisture quickly. “For this time of year we’re going to get a decently strong atmospheric river event,” Miller said. The “atmospheric river” is forecast to make landfall in Santa Cruz County sometime in the Sunday afternoon to evening timeframe, and could bring 3 to 5 inches of rain said National Weather Service Meteorologist Sean Miller. “There is a possibility that we’re going to exceed the debris flow thresholds and we are taking that seriously,” Coburn said. The alert specifically targets the CZU Complex burn scar areas, as well as the cities of Boulder Creek and Scotts Valley. On Friday, The National Weather Service San Francisco also issued a “Flash Flood Watch” for the Santa Cruz Mountains. Areas near hillsides that the CZU Lightning Complex fire stripped of trees, shrubs and other vegetation are most at risk. The data from that report are informing more targeted evacuations, Coburn said. Officials updated those zones in September and incorporated information from a recent debris flow study completed by consulting geologists in the Santa Cruz Mountains. The zones under evacuation warnings as of Friday at 7:50 p.m. Residents are urged to visit evacuation zone maps at to see if their address is impacted and memorize a “zone ID.” Evacuation orders, Coburn said, would likely follow and go into effect by Sunday. Saturday, according to Santa Cruz County Assistant Administrative Officer Nicole Coburn. The Santa Cruz County Sheriff’s office will begin “door-to-door” notifications starting at 8 a.m. FELTON - Evacuation warnings have been issued for parts of Boulder Creek, Ben Lomond, Felton and Santa Cruz County’s North Coast ahead of Sunday’s forecast “atmospheric river” storm, that could set loose dangerous fast-moving slurries of rock, soil and sediment called debris flows.
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