Rainfall thresholds for triggering shallow landslides in Vara Valley (Liguria, Italy)

The Provincial Administration of La Spezia and the Department of Earth Sciences, University of Pisa, promoted a study to define rainfall thresholds for the shallow landslide occurrence. At present, the thresholds were defined for the Vara Valley (about 610 km2), where heavy rainfalls frequently cause shallow landslides with damage to population and environment. On 25 October 2011 a very intense rainfall event hit the Vara Valley causing about 2870shallow landslides. It was analyzed together with other 64 shallow landslide events occurred from 2008 to 2014. The rainfall conditions of these events were determined using an algorithm implemented by the CNR-IRPI of Perugia. The rainfall thresholds were defined using two statistical techniques: least-squares linear fit and quantile regression. The rainfall thresholds obtained by this study are higher than the thresholds obtained for some regions of Italy. The defined thresholds may be implemented in a landslide forecasting system to mitigate the landslide risk.