How wildfire burn scars could have lasting impacts

Burn scars can create heightened risk of flooding for years to come

EL DORADO COUNTY, Calif. -- While most of the Caldor and Dixie fires in Northern California are out, the scorched Earth left behind could have a lasting impact on the area.

Wildfires in portions of the West are doing more than destroying vegetation. The part of the ground where a wildfire burns through is known as a burn scar. These steep regions create a heightened risk of flooding for the years to come. 

According to the National Weather Service, a layer of ash forms on the topsoil while a water-repellent coating is just below that layer of ash. Water-repellent soils form when organic materials such as trees, shrubs, plants and litter burn at high intensities. 

Water-repellent compounds are vaporized and condense on colder soil layers below, which prevents soil from absorbing water. When the rain starts to fall over these regions, the risk for a debris flow (or a mudslide) increases.

The NWS also cautions that a debris flow can start on a dry slope after only a few minutes of heavy rain. These debris flows are dangerous because they can travel faster than a person can run and even outpace a car. 

A debris flow can also pick up burnt material, including trees, and flow over areas that did not experience a wildfire.

Just one heavy downpour in areas with burn scars can cause a debris flow, and there might be little time to act. People living in areas that are affected by wildfires should have an evacuation plan in place.