While Los Angeles faces additional red flag warnings in the coming days due to uncontained wildfires already estimated to cause between $40 billion in insured losses and $250 billion in economic damage, recent history shows that catastrophic natural hazard risks will persist even after the wildfires are contained.
Landslides pose a significant physical and economic threat to the area in the weeks and months ahead, compounding the damage already caused by the wildfires. Post-wildfire debris flows—a type of rapid landslide—can lead to extensive destruction of property and infrastructure. The economic impact of landslides in the United States is considerable, with annual damages estimated in the billions, according to a report released last year by the Congressional Research Service (CRS).
This risk is likely to increase in Los Angeles due to two key factors: increased development in hazardous areas, such as mountainous or hilly terrains, and the growing frequency of weather-related events that can trigger landslides, including intense rainstorms.
January through March are traditionally the wettest months in Southern California. Last year’s "atmospheric river" event, which struck Los Angeles, delivered seven inches of rain over a two-day period, causing billions in economic losses.
Risk Market News spoke with Dr. Farshid Vahedifard, Louis Berger Chair in Civil and Environmental Engineering at Tufts University in Boston, about the region’s risks of landslides and mudslides and his work on a post-wildfire landslide susceptibility model and measuring "cascading geohazards."
Risk Market News: You’ve done work on California wildfires and the subsequent mudslides and landslides that often follow these events. Could you provide some context about the cascading effects we might expect after a wildfire?
Farshid Vahedifard: This is a critical area we’re actively studying right now. Wildfires often set off a chain reaction of events that extend far beyond the fire itself. Once the vegetation is destroyed, the soil becomes unstable and highly susceptible to erosion. When rain follows, it can trigger mudslides and landslides, which are not only destructive but can lead to additional disasters.
These cascading effects often exacerbate the original damage caused by the wildfire. For example, road networks may become impassable, emergency response efforts can be hindered, and infrastructure like bridges and buildings may suffer further damage. Understanding and preparing for these interconnected risks is essential to mitigating the overall impact of these events.

RMN: Your work focuses on cascading hazards, such as landslides and mudslides following wildfires. Considering the region is still battling the fire, can you provide a timeline for when these geohazard risks might materialize? Are we talking about weeks or months?
Vahedifard: That’s a very important issue.
We recently published a document discussing the timeline and dynamics of wildfire-related cascading hazards. First, it’s worth noting that January isn’t typically considered wildfire season, which makes this situation somewhat unusual. However, when it comes to debris flows, they can occur as soon as the next significant rainstorm hits the area.
The key factor is the hydraulic trigger—a heavy rainfall event. January is a time when heavy rains are not uncommon, so it’s entirely possible for debris flows to develop shortly after the rain begins. All it takes is that hydraulic driver, and we could see a massive movement of debris.