Mapping Post-fire Monthly Erosion Rates at the Catchment Scale Using Empirical Models Implemented in GIS. A Case Study in Northern Italy

Post-wildfire geological hazards are an emerging problem for a number of different environments, including areas not typically associated with these events such as the Alpine Region. The risk connected with post-fire processes such as debris-flows and flood-type events threatens people, infrastructures, services and economical activities. Apart from a few examples, such as in the USA and Australia, there is a lack of models available to quantify the increase in susceptibility of the aforementioned phenomena as a result of the modification induced by the wildfires. In this work we test the application of a modified version of the RUSLE, on GIS, to quantify the post-fire erosive phenomena for a case study in the north-western Italian Alps. The results of its application, taking advantage of high-resolution rainfall series and data deriving from field surveys, highlight the marked increase (more than 20 times) in erosion rates, quantified by expressing both the EI (erodibility index), the A (monthly soil loss) and the SL (monthly sediment loss) rise. The months of April, May and June represent the larger share of the total quantities. This is a consequence of the noticeable increase of the EI, which for the post-fire scenario is more than one order of magnitude higher than the pre-fire one.