The Effect of Wildfire On Soil Properties, Infiltration, and Runoff: Considerations For Hydrologic Modeling

The devastation caused by wildfires is well-known. The post-wildfire effects of flooding and debris flows can also present substantial risk to life, property, and infrastructure. Additionally, the threat of wildfires is expected to increase under changing climatic conditions and as the Wildland Urban Interface (WUI) expands into fire-susceptible areas. There is a need to better understand and predict the effect of wildfire on post-wildfire hydrology specifically, and on watershed management, in general.

Wildfires not only effect vegetation, they also directly affect soil properties resulting in immediate and lasting effects on infiltration and runoff processes when precipitation occurs. Wildfire-induced changes to soil hydrology can include the presence of ash, increased water repellency of the soil, soil crusting, and changes to soil structure. Our research objective is the identification and quantification of fire-induced changes to soil parameters necessary for post-wildfire hydrologic modeling. We use a fundamental physically based approach to understand and quantify processes and effects, and to identify data gaps and necessary field measurements. For example, we are now able to quantify the effect of fire-induced soil water repellency on initial post-fire infiltration and, therefore, runoff. Additionally, we can identify fire-induced changes to soil that separately or in combination contribute to alteration of measurable soil parameters. The overall objective of this effort is to improve the accuracy and timeliness of USACE post-wildfire modeling capabilities ranging from near real-time emergency response to longer-term watershed management.