Modelling effects of forest fire and post-fire management in a catchment prone to erosion: Impacts on sediment yield

The present paper contributes to bridging the gaps in modelling post-fire impact and mitigation measures on soil erosion. The specific aims were to predict the effects of forest fires and post-fire mitigation measures on runoff and specific sediment yield (SSY) in a river basin (Celone, S-E Italy). The Soil and Water Assessment Tool model, calibrated with field observations, was used to evaluate runoff and SSY for the current land use (baseline) and six post-fire scenarios. From 1990 to 2011, at the basin scale, the average annual SSY was 5.60 t hayr (SD = 3.47 t hayr). 20% of the total drainage area showed a critical value of SSY (>10 t ha yr). The effects of different fire-severity levels were predicted for one year after the fire, acting on a limited area (2.3% of the total basin area). At the basin scale, the post-fire effect on surface runoff was negligible for all scenarios (<0.4%), and the impact on SSY increased from 5.86 t ha yr up to 12.05 t ha yr. At the subbasin scale, the post-fire logging scenario showed the highest increase of soil loss (SSY increased from 9.48 t ha yr to 57.40 t ha yr). Post-fire mitigation treatments like straw mulching and erosion barriers effectively reduced soil erosion in high- and moderate-severity fires (19.12 t hayr and 20.93 t ha yr, respectively). At the hydrological response unit level, the SSY estimated for the forest in the baseline ranged from 1.18 t hayr to 2.04 t ha yr. SSY increased more than one order of magnitude for the high-severity fire scenarios and ranged from 4.33 to 6.74 t ha yr in the very low-severity fire scenario, underlining the scale effect from the HRU to the basin scale.