Evaluating strategies for single to multi-risk mitigation in urban public open spaces: A behavioural simulation-based approach applied to Italian typological historical urban squares

Urban squares are vulnerable Public Open Spaces in view of morphological, constructive and use features, and they are increasingly affected by the combination of multiple natural and anthropogenic risks. Meanwhile, mitigation strategies designed to face a single risk could also provide benefits from a multi-risk standpoint. This work develops and applies a behavioural simulation-based approach for single to multi-risk assessment and mitigation strategies effectiveness analysis Single to multi-risk scenarios comprising SLow-Onset (SLODs, i.e. increasing temperature, air pollution) and SUdden-Onset (SUODs, i.e. terrorist acts, earthquakes) Disasters are modelled by innovatively combining previously-validated agent-based models representing urban squares morphology and physical vulnerability, climatic features (for SLODs)/hazard probability (for SUODs), and users' exposure, vulnerability and behaviours. Furthermore, novel single and multi-risk metrics are developed to compare scenarios before and after the implementation of selected mitigation strategies, considering the application to Italian typological configurations of historic urban squares. Results demonstrate that the most reliable strategies involve the implementation of greeneries (i.e. trees, fixed/mobile barriers integrated with greeneries). They contribute to single risk reduction ranging from 10 % (i.e. for heatwaves, reducing outdoor temperatures of about 3 °C) to 27 % (e.g. for terrorist acts, reducing casualties-related indicators up to about 60 % thanks to evacuation support and protection from attackers). They also provide multi-risk reduction up to 10 %. This work hence offers decision-makers robust multi-risk mitigation workflow, and a preliminary inventory of mitigation strategies, tested for typological Italian historic urban squares, which could be additionally tailored considering specific features of real-world urban squares.