Modelling the effects of a bushfire on erosion in a Mediterranean basin

A bushfire occurred in the Asinaro River basin in July 1998. The basin area is 55 km2 and about 74% of the whole area was set on fire. The aim of this paper is to test the influence of fire on both soil erosion and the spatial distribution of the areas characterized by the greatest sediment yield values. The RUSLE model and a spatial disaggregation criterion for sediment delivery processes (SEDD model) were used to test the effects of the bushfire. The basin was divided into 854 morphological units for calculating the topographic factor. The RUSLE climatic factor R was calculated using daily rainfall data. The soil erodibility factor was determined by sampling at sites distributed over the basin. The model was applied using different climatic hypotheses (mean year, rainfall events subsequent to the fire or occurring after 6, 12, 24 months) and was used to simulate different post-fire conditions of erodibility and vegetation cover. The analysis showed that immediately after fire, sediment yield rapidly increases in comparison to the undisturbed value (pre-fire). According to the hypothesis made on the cover and management factor, after 24 months the undisturbed condition is gradually reached.