Landslide Risk to the Population of Italy and its Geographical and Temporal Variations

Landslides cause damage to the population in Italy every year. Using an updated version of a historical catalogue of landslide events with human consequences we employed a new approach to investigate landslide risk to the population it Italy over time. We studied the temporal and geographical variation of risk on the basis of two classifications of the Italian territory. We used (i) the five zones based on the average terrain elevation and the distance to the seacoast of the Italian municipalities, and (ii) the topographic areas based on a semi-quantitative, stepwise approach of derivatives of altitude. We estimated individual landslide risk levels in the five zones for the north, centre, and south of Italy and for three different periods between 1861 and 2010. To determine new societal landslide risk levels, we established the probability of experiencing severe landslide events in the eight topographic areas by modelling the empirical distributions of events with a Zipf distribution. The catalogue used covers the period 91BC-2011; the number of events in the catalogue increased with time. The reduced number of events in the early part of the catalogue is attributed to incompleteness, a known bias in non-instrumental records of natural events. To overcome problems of incompleteness in carrying out the risk analysis, we used the recent portion of the catalogue between 1861 and 2010. We believe that the quantification of the risk posed by landslides to the population is an important step for increasing awareness of the problem among Italian administrators and citizens.