Urban morphology parameters towards multi-risk scenarios for squares in the historical centers. Analyses and definition of square typologies and application to the Italian context

The historical built environment (HBE) in urban areas is prone to disasters, which threaten both people and the historical built heritage itself. In such a scenario, risks depend on the combination between different possible (multi-) hazards (including climate change-related ones), the vulnerability and exposure of HBE users, and the physical (morphology-, typology- and construction-related) features of the HBE. In this context, squares are relevant components of the HBE from a meso‑scale perspective, which is based on the layout and morphology of open spaces, buildings blocks and their users. Squares host cultural heritage and attract users, both tourists and citizens. Moreover, squares are nodal points for the emergency path network and are crucial and significantly affected during the immediate aftermath of the disaster occurrence (e.g. by debris on the ground in the case of seismic hazard during the evacuation phase). Current approaches for risk assessment and mitigation entail the consideration of each specific square, but this approach is time-consuming, scattered between the different hazards and complex to apply to a multi-risk perspective. Therefore, this work provides a methodology to identify and classify the most relevant physical features of squares in the HBE, which are able to improve or worsen the performance of the HBEs to multi-risks from multi-hazard scenarios. The research is rooted in the existing literature and strengthened by experts’ judgement analyses. The proposed methodology synthesizes the considered relevant features of the squares in the HBE into quantitative parameters, which allow to verify the vulnerability to multi-risk of the squares. Such parameters are further organized into classes for the typological assessment of the multi-risk. To test and detail the parameters, the method is tested on a relevant case study, which is the Italian context. Indeed, such a case study is relevant not only for being subject to multi-risks (e.g., seismic, terrorist, heatwave and air pollution), but also because the vast majority of the urban areas are composed by HBEs and hosts cultural heritage sites. Moreover, in this context, squares have not only an environmental, but also a social and economic importance in the HBE and are thus particularly relevant. Then, in the relevant case study of Italy, further detailing and calibration of the defined classes of the relevant parameters, as well as their ranges, are tested on 133 squares, which cover the entire Italian territory. Results demonstrate that the identified classes and ranges of the parameters are suitable for describing historical squares by arranging them into typologies for multi-risks assessment. Although the parameters are here presented for the Italian context, they are of general value and could be tested in other contexts, by calibrating the ranges as illustrated for the specific considered sample. Thus, the outcomes of this work allow moving towards the classification of squares into built environment typologies according to the meso‑scale perspective, provide the bases for and promoting the application of expeditious approaches to multi-risk assessment in the HBE.