Modeling the vulnerability of complex territorial systems: An application to hydrological risk

One of the goals of urban planners is to define and to evaluate strategies to mitigate the effects of natural hazards. Adequate methodologies and models should be studied to support their decisions. In this work, an approach to evaluate the overall ‘‘systemic’’ vulnerability of a territory to extreme natural phenomena is presented. This approach is able to support decision makers in evaluating the key preventive planning actions to be exploited on a territory, taking into account both the specific possible damage that is likely to impact the different single relevant elements and the reduction in functionality of the overall territorial system caused by damage to a specific element. To achieve this goal, a graph-based approach is introduced to model the influences that each element may have on the functionality of the overall territorial system. The nodes of the graph represent all the relevant elements in the territory, whose failure or breakdown can seriously influence the functionality of the whole territorial system. The links represent the influences among the functionalities of these elements. An iterative algorithm to compute the consequent systemic vulnerability is also described. In the conclusive section, a case study pertaining to the hydrological risk in the Valle Roja Area located near the North-West coast of Italy is presented