Defining Areas of Negligible Landslide Susceptibility in Italy and in the Mediterranean Region

Landslide susceptibility is the likelihood of a landslide occurring in a given area. Over the past three decades, researchers, and planning and environmental organisations have worked to assess landslide susceptibility at different geographical scales, and to produce maps portraying landslide susceptibility zonation. Little effort was made to determine where landslides are not expected, where susceptibility is null, or negligible. We propose a statistical method for the definition of non-susceptible landslide areas, at the synoptic scale. We applied the method in Italy and to the territory surrounding the Mediterranean Sea and we produced two synoptic-scale maps showing areas where landslides are not expected in Italy and in the Mediterranean area. To construct the method we used digital terrain elevation (3-arc-second SRTM DEM) and rainfall triggered landslide information. The landslide information was obtained for 13 areas in Italy where landslide inventory maps were available to us. Model performances have been evaluated using independent landslide information on Italy and Spain. Best results were obtained using a quantile regression model. The results show that the 41.6% of the whole Italian territory is classified as nonsusceptible while the percentage increase to 63% for the Mediterranean Region.