Wildfires Ignite Flash Flood Risks in Southern California

The California wildfires have brought unprecedented destruction to the Los Angeles and Santa Clarita Regions. As of January 29th, more than 47,000 acres have been burned due to the Palisades, Hughes, and Eaton fires. The Eaton and Palisades fires have earned the spots of 2nd and 3rd most destructive wildfires based on structures damaged, respectively, in state history. Now that the fires are contained, it is important to note the future risks that may follow. 

Wildfires have long term effects on landscapes.  

Forests are crucial in many aspects of life, like storing and cleaning water, feeding streams and rivers, inhabiting wildlife, and holding the California hillsides together. Without these forests, we see an increased risk of flooding, mudslides and landslides. In areas where the fire burned hot enough, organic material such as scrubs, trees, plants, and litter (organic materials like leaves, grass, bark, needles, etc.) will have their water repellent compounds vaporized and the stabilizing vegetation incinerated. The vaporized water repellent compounds then condense on the cooler soil layers below, building a water repellent soil that does not absorb water. All the water absorbent soil that helped absorb excessive rainfall will act as pavement, repelling the water and creating flash floods, mud and debris flows, and mudslides.  

The timing of these wildfires does not bode well for the impacted residents in the area. According to 30 years of rainfall measurements at UCLA from the NOAA Online Weather Database, the month of February is the rainiest month of the year for the western Los Angeles area, seeing an average of 4.73”. Wildfires are traditionally more common in the months of June-July through October-November, which accordingly is the driest time of the year (averaging 2.01” over these 6 months). This means in wildfire season, precipitation is not common following an event, and neither is flash flooding. Climatology, however, says there will be rain following these recent destructive fires, and flash flooding is likely to ensue.  

Standard homeowners’ policies will typically not cover flooding and mudflows. However, in California, if the fire is deemed the “efficient proximate clause”, fire coverage may apply for mudslide and landslide damages. If your residence or business is downstream of a burned area, it is vital to reassess your flood risk, regardless of if you are outside of the traditional flood zone.