The Effect of Soil Water Repellency on Post-fire Runoff

Abstract:

Soil water repellency is believed to contribute to sometimes catastrophic post-fire runoff. This is a critical issue as the frequency and size of wildfires are expected to increase, and as the Wildland Urban Interface expands near and into watersheds susceptible to wildfires. Current runoff models can only empirically account for water repellency as no physical representation was known to mechanistically account for the effect of water repellency on infiltration and runoff. The recent development of a physically-based sorptivity model, which can account for sub-critical water repellency, has been linked to the physically-based Kineros2/AGWA runoff model. Using data from the 2009 Station Fire in the Arroyo Seco watershed near Los Angeles, CA, the effect of soil water repellency is demonstrated. The hydrologic effect of water repellency on total runoff and peak flow is determined. The modeled results highlight the measurements necessary to better predict post-wildfire runoff, especially for flood warnings and emergency response.