Recovery of small-scale infiltration and erosion after wildfires

Abstract

Wildfires naturally occur worldwide, however the potential disruption to ecosystem services from subsequent post-fire flooding and erosion often necessitates a response from land managers. The impact of high severity wildfire on infiltration and interrill erosion responses was evaluated for five years after the 2003 Hot Creek Fire in Idaho, USA. Relative infiltration from mini-disk tension infiltrometers (MDI) was compared to rainfall simulation measurements on small burned and control plots. Vegetation recovery was slow due to the severity of the fire, with median cover of 6-8% on burned sites after 5 years. Consequently, interrill sediment yields remained significantly higher on the burned sites (329-1200 g m-2) compared to the unburned sites (3-35 g m-2) in year 5. Total infiltration on the burned plots increased during the study period, yet were persistently lower compared to the control plots. Relative infiltration measurements made at the soil surface, and 1- and 3-cm depths were significantly correlated to non-steady state total infiltration values taken in the first 10 minutes of the hour-long rainfall simulations. Significant correlations were found at the 1-cm (ρ = 0.4-0.6) and 3-cm (ρ = 0.3-0.6) depths (most p-values <0.001), and somewhat weaker correlations at the soil surface (ρ = 0.2-0.4) (p-values <0.05 and up). Soil water repellency is often stronger below the soil surface after severe wildfire, and likely contributes to the reduced infiltration. These results suggest that relative infiltration measurements at shallow depths may be useful to estimate potential infiltration during a short-duration high-intensity storm and could be used as an input for post-fire erosion models.

Keywords

• interrill erosion
• mini-disk infiltrometer
• post-fire erosion
• rainfall simulation
• water repellency