Why Are Wildfires Followed by Flood Events?

A wildfire burns away the plants and leaf litter that normally absorb rainfall and slow runoff. The intense heat can also bake the soil, creating a waxy, water-repellent layer just below the surface. This hydrophobic soil acts like a paved driveway for water. When rain falls, it cannot infiltrate, so it immediately flows overland, gathering speed and force. The loss of root structures also makes the soil itself more prone to erosion. This combination of factors creates a landscape primed for rapid, uncontrolled water movement.

Flash floods in burn scars often carry more than just water. They pick up loose ash, soil, rocks, and charred debris, transforming into thick, fast-moving slurries. These debris flows can be incredibly destructive, burying roads, pushing boulders into properties, and depositing thick layers of mud inside homes. They pose a severe threat to structures downhill from burned areas. The force of these flows can undermine foundations and cause catastrophic structural damage. The consistency of these flows is often described as similar to wet concrete, making them extremely difficult to stop or divert.

If a wildfire has burned near your home, stay alert to weather forecasts and any flood warnings from local authorities. Before a storm, clear gutters, downspouts, and drainage ditches to ensure water can flow away. Consider installing temporary barriers, such as sandbags, to divert water away from your foundation. Move valuables to higher levels if possible. Have an emergency plan and kit ready in case you need to evacuate. Keep important documents in a waterproof container and know your planned evacuation route.