Determining future evolution of landslides from the past: the historical evolution of shallow landslides in the upper Cassarate catchment (Southern Swiss Alps)

Christian Ambrosi, Samuel Arrigo, Claudio Castelletti and Cristian Scapozza

In mountain environments that were subject to intensive pastoralism, the abandonment of alpine pastures and the natural reforestation caused the main modifications in land use. These two factors may have had a significant effect on evolution of shallow landslides. In the upper Cassarate catchment, the evolution of the number and surface of shallow landslides between 1900 and 2014 was studied with diachronical mapping on historical analysis. Quantitative analysis of precipitation and antecedent standardized precipitation index (IPAS) allowed triggering thresholds of 55 shallow landslide events to be calculated. The good statistical fits between the difference of IPAS and, respectively, the minimal value of IPAS and the sum of precipitations, allows defining the shallow landslide triggering thresholds. Two scenarios of shallow landslide triggering were implemented thanks to numerical modeling with the TRIGRS program and allowed a validation of the triggering thresholds determined by the historical analysis. A forecasting of future shallow landslides evolution was possible by defining 1) potential aggravation zones of observed landslides; 2) potential triggering zones of new instabilities.

2016/1 396-405