Alba Yerro-Colom is a geotechnical engineer in the Charles E. Via, Jr. Department of Civil and Environmental Engineering at Virginia Tech. Photo by Virginia Tech.
News — Heavy rain might seem like a welcome relief after a blazing wildfire, but scorched earth is susceptible to mudslides. Wildfire destroys vegetation like trees and shrubs, whose roots fortify soil and protect against these dangerous, natural events.
, assistant professor in the Virginia Tech , researches how vegetation and rainfall can predict and prevent mudslides.
With an atmospheric river storm now brewing in Southern California after wildfires ravaged the state last month, experts are warning residents to stay alert and informed. The first year after a fire — especially the first rainy season — brings the risk of the fastest-moving, more destructive landslides, Yerro-Colom said.
Why is heavy rain so dangerous after a big fire?
“These events can move really fast, exceeding 35 mph, carrying large items such as boulders, trees, and cars, and can have large runouts extending beyond the burned areas, impacting communities unaware of the imminent risk,” Yerro-Colom said. “What increases the risk even more in California is that these zones are densely populated.”
How do location and California’s soil conditions and desert vegetation increase the risk of mudslides?
“The weather in California is heavily influenced by the presence of the Pacific Ocean, which typically moderates extreme temperatures with seasonal changes, warmer, drier summers and cooler, wetter winters. In addition, this area is also affected by heavy coastal storms or atmospheric rivers that bring high-intensity, short-duration rain episodes,” Yerro-Colom said.
“In regards to soil and vegetation, the presence of loose material and erodible soils, both present in California, makes the conditions critical. Desert vegetation typically has a slow regrowth, making the burned slopes vulnerable for a longer period of time.”
Does the amount of time between the fire and the rainfall also contribute to hazardous conditions?
“The link between wildfires and landslides declines rapidly over time when vegetation recovers.
In as little as five years after a fire, indicate the likelihood that a landslide can return to pre-burned conditions.
“Within the first year after a fire, though, it’s common to see runoff-generated debris flows, especially during the first rainy season when heavy precipitation causes surface runoff, which then picks up loose debris or sediment and can be really destructive. In these conditions, what might be a moderate amount of rain – say, half an inch in a 15-minute period – can be a trigger for these fast-moving, destructive landslides,” Yerro-Colom said.
How much rainfall poses an increased risk for mudslides?
“Short-duration rainfall intensities — those lasting less than 15 minutes — are the most likely to cause a landslide. These brief, intense bouts of rain are a key predictor of how much surface run-off there will be, which contributes to the dangerous debris flows common in the first rainy season after a fire,” Yerro-Colom said.
How can residents stay safe right now? What resources can local authorities provide?
Avoid steep slopes and canyon-like topography during or soon after rainfall events.
Avoid flow paths, even if they are currently dry.
Make an evacuation plan and be ready to leave on short notice.
Monitor slopes and drainage paths.
Check for warning signs, like cracks on the ground, small rockfalls, sudden runoff or muddy water in streams, sudden rumbling noises, ground shaking, strong smells of soil or mud.
Use NOAA weather radios, local emergency services, and wireless emergency alerts. Public awareness of debris flows and rainfall-triggered landslides is very important to reduce human losses during such catastrophic disasters.
About Yerro-Colom
, a geotechnical engineer in the at Virginia Tech, studies how to predict and prevent landslides. Using numerical frameworks and artificial intelligence, her research aims to advance the understanding of rainfall-triggered landslides to better predict their potential damage and increase public preparedness.
For media inquiries or to schedule an interview, please contact:
Margaret Ashburn | [email protected] | 540-529-0814
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