Advances in Rainfall Thresholds for Landslide Triggering in Italy

We reviewed the Italian scientific literature published in the period 2008-2018 on the topic of rainfall thresholds for the landslide triggering, with the aim of analyzing the most significant advances and the main open issues. In the international literature, Italy occupies a relevant position from both a quantitative and a qualitative viewpoint: 65 out of the 163 thresholds published worldwide in the considered period are defined in Italy. The main improvements can be ascribed to rigorous cataloguing of landslides; definition of standard and objective methods for thresholds analysis; quantitative validation of the results and evaluation of the performance of related warning systems; attempts to improve the spatial resolution of the forecasts. However, some shortcomings still limit the research on landslide rainfall thresholds and some open issues recently emerged as priorities to be further investigated: the effects of climatic and environmental changes on the thresholds; their implementation into hazard management procedures and early warning systems; the adoption of combined approaches to account for the hydrological conditions of the slopes; the quantification of diverse uncertainties. This review disseminates the best practices among scientists and stakeholders involved in landslide hazard management, and it draws a national framework of procedures for defining reliable rainfall thresholds, in particular for early warning purposes.