Comparing predictive capability of statistic and deterministic methods for landslide susceptibility mapping: a case study in the northern Appennines (Reggio Emilia Province, Italy)

Statistical and deterministic methods are widely used ingeographic information system based landslide susceptibility mapping.This paper compares the predictive capability of three differentmodels, namely the Weight of Evidence, the Fuzzy Logic andSHALSTAB, for producing shallow earth slide susceptibility maps, to be included as informative layers in land use planning at a local level.The test site is an area of about 450 km2 in the northern Apennines ofItaly where, in April 2004, rainfall combined with snowmelt triggeredhundreds of shallow earth slides that damaged roads and otherinfrastructure. An inventory of the landslides triggered by the eventwas obtained from interpretation of aerial photos dating back to May2004. The pre-existence ofmapped landslides was then checked usingearlier aerial photo coverage.All the predictivemodelswere run on thesame set of geo-environmental causal factors: soil type, soil thickness,land cover, possibility of deep drainage through the bedrock, slopeangle, and upslope contributing area. Model performance wasassessed using a threshold-independent approach (the ROC plot).Results show that global accuracy is as high as 0.77 for both statisticalmodels, while it is only 0.56 for SHALSTAB. Besides the limited qualityof input data over large areas, the relatively poorer performance of thedeterministic model maybe also due to the simplified assumptionsbehind the hydrological component (steady-state slope parallel flow),which can be considered unsuitable for describing the hydrologicbehavior of clay slopes, that are widespread in the study area.