After Wildfires, L.A. Faces New Dangers: Floods and Landslides Loom Ahead

As Los Angeles grapples with the aftermath of recent wildfires, experts are sounding the alarm about an impending threat that could be even more dangerous than the flames themselves: rainfall that has the potential to trigger devastating floods and landslides. While firefighters continue to battle the blazes, teams of geologists and emergency response specialists are surveying the charred landscapes left in the wake of the Eaton and Palisades fires, assessing the extent of the damage and the risks that lie ahead. Jeremy Lancaster, California’s state geologist, emphasizes that the dangers following a wildfire are far from over. The focus has now shifted to understanding how the fire's destruction has altered the landscape. In the rugged terrain of the San Gabriel and Santa Monica Mountains, researchers are mapping areas that experienced varying degrees of burn severity, which will inform hazard maps aimed at protecting residents from the imminent threats of flash flooding and debris flows. Wildfires can transform once-absorbent soils into hard-packed surfaces that repel water, creating conditions ripe for flooding. In the absence of vegetation that would typically stabilize slopes, rainwater can rapidly funnel downhill, increasing the likelihood of dangerous runoff. Experts warn that even a moderate rainstorm can have catastrophic effects in recently burned areas. The combination of steep slopes, scorched earth, and rain creates a perfect storm for debris flows, a phenomenon likened to "a flood on steroids." These flows can carry a mix of soil, rocks, trees, and other debris, gaining momentum and causing significant destruction in their path. The aftermath of the Thomas fire in 2017 serves as a grim reminder of this reality; a debris flow in Montecito resulted in the tragic loss of 23 lives and extensive property damage. Insurance often fails to cover the impact of these debris flows, which are classified as landslides, leaving many homeowners vulnerable. The rise in frequency and intensity of wildfires, linked to climate change, is compounding the risk. As Dr. Jason Kean, a research hydrologist with the United States Geological Survey, indicates, the increasing size and severity of wildfires exacerbate the landscape’s vulnerability to post-fire hazards. Southern California, particularly Los Angeles, is regarded as a hotspot for these types of disasters. With millions of residents living in areas prone to flash floods and debris flows, proactive measures are critical. Established debris basins at the edges of fire-affected mountains aim to mitigate the impacts of these flows, but the threat remains ever-present. In response to the growing risk, the National Weather Service has collaborated with the Geological Survey since 2005 to implement an early warning system designed to alert communities of potential hazards. By setting rainfall thresholds that can trigger landslides, authorities aim to provide timely warnings to residents in high-risk areas. As of now, although the immediate forecast shows no rain, meteorologists caution that conditions could shift rapidly, and even a light rainfall could set off a chain reaction of hazards. Residents are advised to stay vigilant, monitoring weather updates and preparing for the possibility of evacuations. The unpredictability of nature, combined with the consequences of wildfire devastation, underscores the critical need for community preparedness and awareness in the face of these looming threats. As Los Angeles stands at a crossroads, the dual specters of fire and flood serve as a reminder of the challenges posed by a changing climate and the landscape's inherent risks.