Valutazione dei rischi ambientali con particolare riferimento alle zone colpite da problemi di dissesto idrogeologico e dal ripetuto passaggio di incendi boschivi.

Wildfires are one of the most widespread factors of ecosystem degradation around the world. The degree of change in both chemical and biological properties of soil inducted by forest fires depends on the temperature and the persistence of the fire as well as on the soil moisture content of fuel. This research, in a first step, deals the study of the stability variation of a hill slope crossed by a forest fire. The first site of investigation is located at western boundary of the rift of Campidano, south-western Sardinia, Italy, to the North-West of the urban area of Villacidro. The geological features are constituted by metamorphic rocks (Hercynian basement) overlying granitoid rocks with a sub-horizontal and weakly wavy contact surface. In order to perform the stability analysis, two geotechnical models were derived by the integration of the results of geotechnical surveys (NSPT measurements and direct shear tests) with electrical resistivity tomographies. Classical approach based on Limit Equilibrium Method is used to determine the safety coefficient. Furthermore, the effects of the forest fire on the slope stability have been discussed modifying the 2D models and introducing an ultra-shallow thin layer with the shear strength parameters determined on burned soil samples, collected after the fire crossing. In particular, this analysis has shown a marked reduction of safety factor at the interface between the burned soil layer and the underlying material for both geotechnical models, considering the infinite slope method with several saturation conditions of the shallow layer. In this study also were determined the concentrations of geochemical components in the soils affected by forest fires. The fire-burn severity was medium, but the effect of geochemical variation on soil is evident. We observe the variation of total content of Mn that increase in soils affected by a forest fires, respect the control soils. Moreover the C,N and P contents of soil decrease in the time, according with most of the international bibliography. Mapping the values of the geochemical components it was possible to see their mobilization after the rains. With these data we will try in the future to build a model of mobilization of contaminants that is able to predict the decrease in the concentration of the element considering the time elapsed from the fire, the intensity of rainfall and slope. In a third step the study aim is to develop methods for the analysis and the collection of field data, by means of a multidisciplinary approach, to evaluate land erosion hazard. The second experimental area is located also in Mediterranean basin, on a steep slope in a hilly area of north-western Sardinia (Municipality of Ittiri, province of Sassari, Italy),where a human caused fire occurred in august 2013. The area is mainly covered by the typical Mediterranean vegetation. Precipitations were recorded using tipping bucket rain gauge installed at the site. Soil erosion rates from experimental plots were measured and estimated with silt fences technique taking into account different slopes and vegetation distribution. The study aims to compare the results obtained by ERMiT (Erosion Risk Management Tool) model application and post-fire sediment yields measured in the study area. The application of the model shows that the area experienced most of erosion after the first rain events after fire occurring. Comparing experimental and model estimated data, there is evidence of ERMiT model overestimating in respect of sampled data for the first year. Future experimental data are needed to confirm this assumption and to contribute to calibrate ERMiT in a Mediterranean typical vegetation and climate environment.