Systemic vulnerability in urban areas exposed to combined risk of landslide and flood. La vulnerabilità sistemica in aree urbanizzate esposte a rischio combinato di frane e inondazioni.

This paper aims to analyze the systemic vulnerability of an area as complex as urban when a fl ood and landslide occurs. The proposed approach of vulnerability evaluation, differs from those who prefer the traditional physical sense because of it provides an analysis of “systemic vulnerability” measuring the relationship between extreme event’s magnitude and direct and indirect consequences of this event on the territorial system. The model is an application of a mathematician-decisional model action to estimate the vulnerability of a complex territorial system to the landslide and fl ood events. The model uses a group of “pressure pointers” in order to defi ne, qualitatively and quantitatively, the infl uence exercised on the territory system from factors like as an example, those physicists, social, economic, etc. In particular, the model assesses the degree of exposure to the combined risk of natural phenomena as landslide and fl ood. This occurs, for example, when different natural events trigger at the same time, or are linked one to the other. For instance, landslides may obstruct the regular stream fl ow and produce a dam breaking effect downstream. This model, anchored in a GIS system, is characterized by the following phases: 1. topological characterization of the studied territorial system and assessment of the scenarios in terms of spatial landslide and fl ood hazard; 2. analysis of the direct consequences of a scenario event on the system; 3. defi nition of the assessing model of the systemic vulnerability in combined landslide and fl ood areas. The vulnerability of the system due to combined landslide and fl ood areas was evaluated in the urban area of Potenza city, in the south of Italy, which is well known for being characterized by a widespread state of hydrogeological upheaval. This is an area complicated by the presence of many elements that may be involved directly or indirectly during the disaster: roads, houses, offi ces, industries. The application shows that, during a combined landslide and fl ood event, the loss of functionality of the elements that fall within the risk areas may affect the functionality of elements farther but related, directly or indirectly, with them. The proposed procedure is to act as a support in planning decisions, in analyses of the consequences of combined landslide and fl ood events on complex territorial systems, and in defi ning intervention priorities.