Slope stability following extreme precipitation events: analysis of causal factors in two study cases in Central Apennine Italy

Abstract

All over the world extreme events are generating more and more significant problems in terms of slope stability. Central Italy, in the same way, has shown in recent years an increase in the intensity of rainfall phenomena that can cause hydrogeological instability. The aim of this study is to propose a new methodology through which the triggering thresholds of the landslides investigated can be evaluated. The procedure is based primarily on the evaluation of extreme events that have characterised the area in past years, attempting to find the connection between slope dynamics and the geomorphological setting that are investigated in detail. At the same time, the land cover and vegetation conditions of the area are also evaluated in correspondence with each extreme event, through the NASA products, Landsat 7 and Landsat 8. The research focuses on an extreme precipitation event that occurred in a small area in central Italy in November 2013, which led to the triggering of some landslides. Through the evaluation of some satellite indices (NDVI and NDMI), land use, geology, geomorphology of the territory, characteristics are identified that could be exported to neighbouring areas and that allowed the identification of triggering thresholds for the analysed territories. The result of the study made it possible to identify the triggering threshold of the two landslides in the investigated areas between 150 and 200 mm of daily precipitation under low vegetation conditions. The geomorphological characterisation showed that these landslides are due to debris accumulation in particular slope and bedrock conditions, and also highlighted the type of landslides most susceptible to movements dictated by large meteorological events in predisposed hydrogeological contexts. However, these two landslides have a different genesis related to the different grain size of the material, which in one case develops an earth flow, in the other a debris flow.