Wildfires can Cause Dangerous Debris Flows

Oct 22, 2020 at 8:00am

Jules Bernstein, UC Riverside

Wildfires don’t stop being dangerous after the flames go out. Even one modest rainfall after a fire can cause a deadly landslide, according to new UC Riverside research.

“When fire moves through a watershed, it creates waxy seals that don’t allow water to penetrate the soil anymore,” explained environmental science doctoral student and study author James Guilinger. 

Instead, the rainwater runs off the soil surface causing debris flows, which are fast-moving landslides that usually start on steep hills and accelerate as they move. 

“The water doesn’t behave like water anymore, it’s more like wet cement,” Guilinger said. “It can pick up objects as big as boulders that can destroy infrastructure and hurt or even kill people, which is what happened after the 2018 Thomas fire in Montecito.”

Guilinger and his team of mentors and collaborators wanted to understand in detail how multiple storm cycles affect an area that’s been burned by wildfire, since Southern California tends to have much of its rain in the same season.

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