Preparedness

California Faces 'Extra Risk' of Flooding after Series of Massive Wildfires, Officials Warn

Fires don’t just destroy trees and brush, they also singe root systems that hold hillsides in place.

by Joseph Serna, Los Angeles Times / October 24, 2018

(TNS) - Less than a year after a roaring mudslide left 23 people dead or missing in Montecito, state and federal officials will gather in Santa Barbara County on Wednesday to issue a warning to all Californians: Massive summer wildfires have left many communities facing an increased risk of flooding.

The announcement, part of California Flood Preparedness Week, comes as the state’s wet season is quickly approaching.

The massive Thomas fire that started in December was still burning when a storm cell pounded the scorched hillsides above Montecito and dissolved it into a deadly river of mud and rock in January. Now, authorities are warning that recent wildfires have created a recipe for similar disaster.

“It’s not just our coastal areas, or by rivers and streams. It’s hillsides and valleys. Suburban and urban,” said Chris Orrock, a spokesman with the Department of Water Resources. “California experienced [thousands of] fires this summer alone. In the last year we’ve had three of the largest fires in California history.”

Those fires don’t just destroy trees and brush, they also singe root systems that hold hillsides in place, Orrock said. Also, when the fires are hot enough, they create a waxy top coat on the soil that repels the rain, sending the water cascading downhill where it can dislodge heavy boulders or clog drains and bridge passageways with mud and debris.

In Montecito, the concern last year was that any rain falling at a rate of more than a half-inch per hour could trigger a mud flow. It rained far harder than that in early January and triggered a slide that killed 21 people and left two missing. Though vegetation has returned to those same hillsides, it isn’t much, and the potential for a mud flow will remain for years to come, experts say.

Now, more Californians than ever are sharing the risk of mud and debris flows because wildfires have grown bigger and more intense, Orrock said. These areas include the foothill and downslope neighborhoods around the Carr fire in Shasta and Trinity counties; the Mendocino Complex fire in Mendocino and Lake counties; the Ferguson fire in Yosemite National Forest; and the Holy fire in Orange County. The risk of mud and debris flows will last for years.

“In California, every single county has had a flood event occur in the last 20 years,” Orrock said. “We like to tell people they need to be aware. They need to know where they are — are they near a burn scar, near areas of potential flooding?”

Once the fire has passed and the rain arrives, residents should stay vigilant and listen to their local emergency officials, Orrock said. “When these storms come in and your local government says it’s time to evacuate, you need to evacuate.”

He pointed to the mudslide in Montecito, when only an estimated 10% of residents heeded the sheriff’s officials’ warnings to leave the area. Though many of those who died were in a voluntary evacuation zone, first responders had to make numerous rescues in the mandatory zone, in addition to recovering bodies.

In the Carr fire in July, residents fled for their lives with only minutes to spare. Many of them lived in areas that were under mandatory evacuation but had not heeded the warning.

Wednesday’s briefing on flood risk will include members of the DWR, U.S. Army Corps of Engineers, the Federal Emergency Management Agency and the California Governor’s Office of Emergency Services.

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