The methodology employed in this research is structured around a comprehensive framework designed to enhance the resilience of the road network in Emilia Romagna to climate-induced flooding [Figure 1]. The research methodology encompasses five distinct tasks: event analysis, underground analysis, hydraulic analysis, microsimulation model development, and the formulation of an emergency plan. Each of these tasks plays a crucial role in understanding the complexities of flood-related scenarios and devising effective strategies to mitigate their impact.
The development of a microsimulation model is instrumental in assessing various emergency response scenarios. During weather-related evacuations, it is crucial to precisely predict the traffic that needs to be evacuated and identify suitable escape routes within the city. The development of the model encompasses several critical phases: initially selecting a suitable simulation tool, gathering accurate data for both input into the model and its calibration, building the simulation model, conducting thorough calibration and validation, developing and extensively testing emergency scenarios, and ultimately performing a detailed evaluation of the results.
2.1 Event analysis
The first task of the methodology involved a thorough analysis of historical flood events in the region around Palermo, with a particular focus on events similar to those that occurred on 15th July 2020 [Figure 2]. Palermo, the capital of Sicily, is a major city spanning 160 km² and home to 629,500 residents. It serves as a hub for numerous regional administrative functions and experiences significant traffic flow as a key connector between western and eastern Sicily. This city was selected as our study area due to its frequent exposure to natural disasters, substantial population size, and high vulnerability to significant disaster-related damage (Francipane et al., 2021) [15.].
On this date, within the heart of Palermo, a sudden and intense storm unleashed its fury within a remarkably short timeframe. The nature of this event presented a formidable challenge in terms of predictability and preparation. The resulting chaos caused significant damage to the impacted area, endangering the safety of its residents and the many drivers who were travelling through Viale Regione at the time. This area is situated along Viale Regione Siciliana, a crucial roadway in the city of Palermo. The flooding of nearly every underpass along Viale Regione Siciliana stands as visible proof of the event's seriousness
Given the unpredictable nature of such events, proactive measures must be taken in the context of the specific study. This entails the vigilant maintenance of the urban drainage system, the dissemination of accurate information to empower citizens to take prudent action during storms, the clear delineation of vulnerable areas susceptible to rain-induced crises, and the implementation of traffic light systems to signal the potential danger of impassable underpasses. Additionally, a broader focus on comprehensive mobility planning aimed at safeguarding human lives is advocated, recognizing that a proactive approach is the linchpin of resilience in the face of such unpredictable and devastating events (Calvert & Snelder, 2018) [16.].
2.3 Hydraulic analysis
This task focuses on the subways situated within the drainage area of the Passo di Rigano Canal, a predominantly subterranean artificial waterway that spans nearly its entire length. This canal plays a pivotal role in channelling water sourced from various tributaries, including the Luparello, Celona, Borsellino, and Mortillaro canals [Figure 3]. Specifically, the Luparello Canal and the initial upstream segment of the Borsellino Canal intersect with the Via Leonardo Da Vinci Subway, while the Celona Canal traverses the Viale Michelangelo Subway. Originating as a response to the devastating 1931 flood, the construction of the Passo di Rigano Canal was aimed at efficiently collecting water from mountainous regions. The canal's intricate network effectively funnels this water toward the Cantieri Navali area.
The event on 15th July 2020 mentioned earlier had an estimated recurrence period of approximately 120 years, during which Uditore Park (SIAS station) [Figure 3] experienced a staggering 134 mm of rainfall within a mere 2-hour timeframe.
2.4 Microsimulation Model
The development of an effective emergency plan necessitates a systematic approach that transforms a nondisruptive network scenario, the “Base scenario”, into a series of network disruption scenarios that align with potential flood scenarios. This transformation was accomplished through a geoprocessing technique that systematically removed road network segments intersecting flood-affected areas. However, given that the inherent complexity of flood-prone regions often leads to fragmentation of the network into numerous sectors, our research employs a more pragmatic approach. Here, the cost matrices for each network scenario are efficiently processed. In areas where rising water levels render vehicle passage unfeasible, nodes in those locations are assigned a high cost (>10,000 sec.). Consequently, when calculating the cost of utilizing a particular route, the affected section is deemed invalid, and the cost of reaching the subsequent node via an alternative route is computed. This methodology is essential for preventing cost inflation and facilitating the identification of poorly connected or isolated zones within the network. This process is modelled in traffic microsimulation software (Dynasim) to streamline the analysis and ensure comprehensive coverage of potential emergency scenarios.
2.5 Emergency Mobility Plan
Building upon the insights gained from the previous tasks, this task aims at developing a comprehensive emergency mobility plan. This plan outlines strategies and measures to evacuate vehicles and ensure the safe movement of people during flood events. It addresses issues such as traffic management, evacuation routes, and communication strategies to minimize the impact on the road network and enhance public safety.