MODELLING FOREST FIRE AND POST-FIRE MITIGATION MEASURES: Impacts on sediment yield

De Girolamo Anna Maria(a)*, Cerdan Olivier(b), Grangeon Thomas(b), Vandromme Rosalie(b), Lo Porto Antonio(a)
(a) Water Research Institute, National Research Council, Francesco De Blasio 5, 70132 Bari, Italy
(b) Bureau de Recherches Géologiques et Minières, Département Risques et Prévention, 3 Avenue Claude Guillemin, 45100 Orléans, France

Forest fires may alter the hydrological processes, modify soil properties, and increase soil losses. To mitigate the effect of fire on soil erosion, post-fire rehabilitation measures are generally adopted. Hydrological models are useful tools to estimate the hydro-sedimentary response at the different spatial scales (basin, subbasin, hydrological response units) and temporal scales and to evaluate the effects of the measures on soil losses contributing to managing the post-fire risk management.

Within the SERV-FORFIRE Project, a framework was defined and tested for predicting forest fire impact on hydro-sedimentary response and the effects of some post-fire mitigation measures on runoff and specific sediment yield (SSY) in a case study: the  Celone River Basin (S-E Italy).

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The Soil and Water Assessment Tool model, calibrated with field observations, was implemented to estimate runoff and SSY for the land use in the current conditions (baseline) and for six post-fire scenarios. From 1990 to 2011, at the basin scale, model results showed that 20% of the total drainage area was under critical soil erosion (SSY >10 t ha-1 y-1). 

Different fire-severity levels were simulated on a limited burnt area (2.3% of the basin). At the basin scale, the post-fire effect on surface runoff was negligible for all the scenarios except for high-severity fire and post-fire logging (Fr1), and the impact on SSY was an increase up to 12.05 t ha-1 y-1. At the subbasin scale, Fr1 scenario showed the highest increase of soil loss (57.4 t ha-1 y-1), meanwhile, the post-fire mitigation treatments such as straw mulching and erosion barriers were effective to reduce soil erosion in high- and moderate-severity fires (19.1 t ha-1 y-1 and 21 t ha-1 y-1, respectively). At the hydrological response unit level, SSY estimated for the forest in the baseline ranged from 1.18 t ha-1 y-1 to 2.04 t ha-1 y-1. It increased more than one order of magnitude for the high-severity fire scenarios and ranged from 4.33 to 6.74 t ha-1 y-1 in the very low-severity fire scenario.

This work highlighted that several efforts are needed to prevent forest fires and that mitigation measures to reduce soil erosion must be promoted to better manage the post-fire.

 

SERV-FORFIRE project, Wednesday 15 December 2021