In the aftermath of devastating urban wildfires, a rainstorm might seem like a welcome relief. However, fire-scorched landscapes are highly vulnerable to floods, which can bring further destruction. Los Angeles has experienced this repeatedly, from the 1933 Griffith Park Fire to the 2009 Station Fire in the San Gabriel Mountains and the 2018 Woolsey Fire in Malibu.
Mitul Luhar, an expert in fluid dynamics and associate professor of aerospace, mechanical, civil, and environmental engineering at USC, is studying these risks. At the City of Los Angeles’s Hydraulic Research Laboratory in Frogtown, Luhar and his team have developed a 1:120 scale hydraulic model of a section of the L.A. River to simulate flood scenarios.
Luhar explains why floods often follow wildfires and what engineers can do to mitigate risks.
How Wildfires Lead to Flooding
Wildfires destroy vegetation, altering soil properties and increasing flood risks in several ways. “The exposed soil becomes extremely dry and less permeable, preventing it from absorbing rainfall efficiently,” Luhar says. “As a result, more water flows over the surface as runoff, and without vegetation to slow it down, the flow becomes faster and more destructive.”
In addition to increasing runoff, wildfires leave behind debris, which heavy rains can pick up and turn into dangerous mudslides and debris flows. These flows, rather than just water, often cause the most destruction in post-wildfire floods.
Mitigation Strategies
To reduce post-wildfire flooding, Luhar suggests rapid debris cleanup, especially when heavy rain is forecasted. Another approach involves carefully wetting the soil before storms arrive. “Lightly spraying the ground over several days can help improve infiltration and reduce runoff,” he says. However, this method requires precision over-saturation could trigger landslides instead.
LA’s Growing Climate Threats
Southern California faces a troubling climate paradox. “Global warming intensifies both wildfires and rainfall, creating what we call ‘hydroclimate whiplash,’” Luhar explains. This pattern sees L.A. oscillating between extreme wet winters that fuel vegetation growth and dry winters that turn that vegetation into wildfire fuel. In turn, the wildfires destroy plant cover, increasing flood risks when heavy rains return.
Engineering Solutions
Luhar and his collaborators are working to make L.A. more resilient by improving water management and flood control. One major initiative involves revitalizing the L.A. River to better manage floods while capturing and storing water for drier years.
Meanwhile, other USC researchers are exploring wildfire prevention and suppression strategies. One emerging area of study focuses on aerial firefighting in extreme winds. “The Palisades and Eaton fires spread rapidly due to strong winds, which also grounded aircraft that could have slowed the fires,” Luhar says. His team is researching new fire suppression techniques that remain effective even in unpredictable, high-wind conditions.
Beyond research, Luhar is actively involved in policy discussions. His work on the L.A. River is in partnership with local, county, and state agencies. Additionally, he co-chairs the New Voices program at the National Academies of Sciences, Engineering, and Medicine, which advises on infrastructure resilience and disaster response.
“We need better science communication, stronger public trust in research, and improved coordination between scientists, policymakers, and communities,” Luhar says. “Our goal is to bridge the gap between research and real-world solutions that protect people from climate-driven disasters.”
As wildfires and extreme weather events become more frequent, engineers, policymakers, and communities must work together to adapt. With innovative solutions and proactive planning, L.A. can reduce its vulnerability to the growing threats of fire and flood.