The hazard indices as a tool to support the territorial planning: The case study of Ischia island (Southern Italy)

The best knowledge of hazardous events and the precise mapping of the zones that they could involve are essential to plan the actions aimed at reducing the territorial vulnerability and promoting the development of a resilient community. In this framework, the main goal of the present research is to propose a quantitative spatial modeling approach that, starting from hazard indicators, defines multi-hazard indices to compare the degree of hazard among different zones allowing the establishment of intervention priorities for risk reduction. The method was applied to the case study of Ischia island, located in the north-western zone of Napoli bay (Southern Italy): indeed, the exposure to many natural hazards (seismic, volcanic, landslide, coastal erosion and marine inundation) coupled with the intense urbanization make the island a good test area to validate the methodology here proposed. Taking into account the different recurrence times of natural events, two multi-hazard indices were quantified, the total multi-hazard index that illustrates the hazard status of the territory considering all the natural events and the partial-hazard index that only takes into account those occurring yearly to decadally. Moreover, with the aim of easily and globally visualizing the hazard status of the territory, the indices were depicted into maps that could facilitate the communication to stakeholders and consequently the reduction of social vulnerability. The municipalities of Serrara Fontana, Barano d'Ischia and Casamicciola Terme show the highest total multi-hazard index of the study area, all the other municipalities display a value (always exceeding 0.5) that, although lower than in the previous three, signifies that the entire island needs attention with regard to natural hazards. The partial multi-hazard index confirms the highest value for Serrara Fontana and Barano d'Ischia. Multi-hazard hotspots, identified at the censual district scale for the Forio d'Ischia municipality, enlighten the areas where a comprehensive risk assessment is needed. We also took advantage of spatial and temporal analysis in order to compare the evolution of population and urban development to spatial distribution of hazard zones over the last 80years. This analysis evidenced that the urban development was insensitive to the dangers impending on the territory, as the expansion in the zones with medium-high level of hazard testifies. Because of this, the present status of the island postul