Simulation-based effectiveness evaluation of typological “best strategies” for single and multi-risk mitigation in historic squares

Squares in historical city centres are challenging scenarios for disaster risk mitigation. Besides their physical vulnerability, they are “hot spots” in both terms of morphology and human factors, being also characterized by overcrowding and the presence of vulnerable users. Thus, mitigation strategies should be designed to be effective in various single-risk and multi-risk scenarios, depending on hosted users’ emergency needs and behaviours. This paper aims at determining optimal mitigation strategies against rising temperatures, air pollution, terrorist acts and earthquakes and their combination, using a behavioural simulation-driven methodology. Single risk Key Performance Indicators are defined to combine users’ exposure and vulnerability to square features (i.e. morphology, physical vulnerability, climatic attributes, hazard probabilities, and damage levels). Multi-risk metrics are then developed combining these indicators. Input data for indicators and metrics are calculated through validated simulation models, and applications to relevant typological configurations of Italian historic squares are performed considering the scenarios before and after the implementation of literature-based strategies affecting users’ behaviours. Results show how implementing greenery and engineered planters can be selected as “best strategies” to face the given risks, since they can both decrease effects on users’ health and support evacuation flows in emergency conditions. Being tested in typological (idealized) conditions, this study provides an initial strategies inventory that can be further customized in real-world squares. Decision-makers can evaluate their specific impact using the proposed simulation- based methodology and the proposed indicators and metrics.