GIS Methodology to Assess Landslide Susceptibility: Application to a River Catchment of Central Italy

This paper illustrates a geographic information system (GIS) supported methodology for the assessment of landslide susceptibility. The methodology involves four operational steps: survey, site analysis, macro-area analysis and susceptibility analysis. The Survey includes the production (or acquisition) of a large-scale litho-technical map, a large-scale geomorphological map, a detailed inventory of past and present landslide events, and a high resolution DTM (Digital Terrain Model. Site analysis leads to the definition of discriminating parameters (commonly, lithological and morphometric conditions necessary but not sufficient to trigger a landslide of a given type) and predisposing factors (conditions that worsen slope stability but are not sufficient to trigger a landslide of a given type in the absence of discriminating parameters). The different predisposing factors are subdivided into classes, whose intervals are established by descriptive, statistical analysis of landslide inventory data. A numerical index, based on the frequency of landslide occurrence, quantifies the contribution of each class to slope instability. Macro-area analysis includes the generation of Litho-Morphometric Units (LMU) by overlaying discriminating parameters, manual drawing of LMU envelopes (macro-areas), generation of predisposing factor maps from the spatial distribution of predisposing factors, and heuristic weighting of predisposing factor indices. Susceptibility analysis includes the generation of Homogeneous Territorial Units (HTU) by overlaying macro-areas and predisposing factor maps, and the application of a susceptibility function to the different HTU. The resulting values are normalized before the generation of the landslide susceptibility maps. The methodology has been applied to the Fiumicino River catchment, located in the western side of Latium Apennine (Central Italy) between 200 and 1300 m a.s.l. and developed on Late Miocene calcarenites, sandstones with clay intercalations, and marls. The resulting landslide susceptibility maps will be employed in environmental management. They also represent the preliminary step for the assessment of landslide hazard and risk.