Geomorphology and landslide susceptibility assessment using GIS and bivariate statistics: A case study in southern Italy

AbstractThis article assesses the landslide susceptibility inthe Calaggio Torrent basin (Campanian Apennines,southern Italy). landslide susceptibility was assessedusing two bivariate-statistics-based methods in a GIS environment. In the first method, widely used weighting values (Wi) have been calculated for each class of the selected causal factors (lithology, land-use, slope angle and aspect) taking into account the landslide density (detachment zones + landslide body) withineach class. In the second method, a modification ofthe first method, only the landslide detachment zone(LDZ) density has been taken into account to calculatethe weighting values. This latter method is characterizedby a major geomorphological coherence. In fact, differently from the landslide bodies, LDZ mustnecessarily occur in geoenvironmental classes prone to failure. Thus, the calculated Wi seemed more reliablein estimating the propensity of a given class to generate failure. The thematic maps have been reclassified on the basis of the calculated Wi and overlaid to produce landslide susceptibility maps. The methods indicate that most part of the study area is characterized by a high/very high landslide susceptibility and in the location and extent of the low-susceptible areas.However, an increase of both the high/very high andmoderate/high susceptible areas occurs in using thesecond method. Both the susceptibility maps produced have been compared with the geomorphological map,highlighting an excellent coherence which is higher using method-2. In both methods, the percentage of each susceptibility class affected by landslides increases with the degree of susceptibility, as expected. However, the percentage at issue in the lowest susceptibility class obtained using method-2, even if low, is higher than that obtained using method-1. This suggests thatmethod-2, notwithstanding its major geomorphologicalcoherence, probably still needs further refinements.