Identification of urban critical context using multi-risk composite-index

Given the complexity of the urban environment and the intricate social fabric within cities the multi-risk assessment in urban settlements is a particularly challenging task. The nature of urban risk is inherently multi-dimensional, encompassing physical, social, economic, institutional, and environmental factors. Each element of the systems constituting the urban settlement is characterized by different exposure and vulnerability to natural hazards. Moreover, the key features of the exposed elements can vary spatially and temporally, leading to an even more complex estimation of potential across an urban area. Additionally, the interrelated nature of various hazards adds another dimension of complexity to traditional risk frameworks.

This study presents a framework for integrating multiple dimensions in risk analysis. A straightforward risk index that combines multiple hazards and physical, social, and environmental exposure and vulnerability information is proposed. The index is obtained by combining single indicators representative of the aforementioned dimensions, resulting in a more holistic representation of risk. Moreover, selected indicators are combined, defining suitable weights that may reflect stakeholders’ priorities in policymaking. Recognizing the extreme complexity of urban systems and the difficulties in capturing different exposure/vulnerability conditions with a single index, a viable approach is to define a priori the multi-hazard scenario and risk metric of interest and select only the most representative exposure/vulnerability indicators to build the composite risk index. To this end, risk storylines and related impact-chains can be used as a practice-oriented support to guide the selection of the basic elements contributing to the relevant impact scenario and to account for unexpected cascading effects activating different types of vulnerabilities and eventually amplifying the final impact.

This approach allows for ranking regions exposed to multiple hazards and identifying urban critical contexts, i.e., urban areas where potential risk generated by different sources is higher and that are more in need of application of disaster risk reduction strategies. The prioritization of urban areas exposed to natural hazard risks provides several advantages for effective risk management and mitigation strategies. Concentrating efforts on high-risk areas is often more cost-effective, as it minimizes the need for widespread interventions and allows for the efficient allocation of limited resources. Furthermore, by applying a variation of single indicators composing the index, the proposed approach enables accounting for the effect of mitigating actions in risk analysis. the Thus, this tool also represents a helpful mean to evaluate the effectiveness of risk reduction policies.

This study was carried out within the RETURN Extended Partnership and received funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005