Wildfires and Cascading Post-Wildfire Impacts

Wildfire in mountain communities can be devastating. Unfortunately, in many cases the fire is the beginning of cascading events that can include flooding, severe erosion, and debris flows. These post-wildfire impacts can pose risks to life safety, homes, infrastructure, and ecosystems. There are ways that we can be prepared for, and in some cases lessen the severity of these events. This can be accomplished with robust emergency preparedness actions and a holistic approach to watershed restoration.

Due to the topography, number of homes, tree density and weather conditions in the Coal Creek area, high wildfire intensity and severity would not be unlikely. High intensity describes the, “energy released from the fire or characteristics of the fire behavior such as flame length and rate of spread and fire severity refers to the ecosystem impacts of a fire such as mortality of trees or loss in biodiversity” (J.E. Keeley, in Encyclopedia of Ecology, 2008).

Both high intensity and high severity wildfire have the potential to alter physical and chemical composition of soil and increase the rate and volume of water that runs down a hillslope for at least two to three years after a wildfire event. Fire removes vegetation, litter and duff on the ground and soil can become hydrophobic after a wildfire, temporarily becoming unable to absorb precipitation and runoff. When this occurs, there is a greater likelihood of sheet flow of water from hillslopes increasing flood risk downstream. With altered soil composition and watershed hydrology, hillslopes are more prone to severe erosion and debris flows.