Palermo Flood Analysis
Flood Impact Analysis for the Development of Emergency Plans
On July 15, 2020, a flash flood severely impacted Palermo's main arterial road, Viale Regione Siciliana, halting traffic with extreme rainfall and flooding. This was an exceptional rain event that started around 4 p.m. and was short-lived (about 2 hours), took place over a narrow area and had rain peaks of more than 160 mm/h (the average rainfall value during the same period in the same area is about 3 mm/h).
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citiEU collaborated with the University of Palermo and the University of the Aegean on this project, to analyse the impact of the flash flood in Palermo, and to develop emergency plans for similar events that impact road accessibility. One of the key aims was to improve future emergency response and road network resilience.
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The first step in designing this emergency plan was to study what happened in terms of mobility during this event. The project used TomTom Traffic Stats to analyse real-time traffic data during the flood event, focusing on median speeds and the availability of infrastructure.
TomTom marks the segments in grey where there is no sample. In this case, the absence of a sample is due to the presence of the flooded underpass; therefore, vehicles could not pass through. This information is valuable because it makes it possible to identify flooded underpasses, when flooding occurred and how long it lasted. In this way, it is possible to assess the impact of flooding on mobility during the event and take appropriate measures to deal with similar situations in the future.
From these data, a microsimulation model was constructed in a reference and emergency scenario. The reference scenario was analysed under average traffic flow conditions to establish a baseline for comparison. The emergency scenario considers, from the Traffic Stats analysis, two key elements:
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Median speeds during the event. These speeds are lower than the usual speeds, i.e., historical speeds during a similar date period and at similar times. Usually, weather events induce drivers to drive more carefully and, therefore, slower.
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Unusable infrastructure. The emergency simulation scenario considers all unusable infrastructure, such as flooded underpasses.
Key Findings​
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Flooded Underpasses: The Traffic Stats analysis helped identify flooded underpasses and impacted routes, allowing for precise flood duration mapping and clearer visibility on inaccessible areas during extreme weather.
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Traffic Impact: Median speed maps showed significant slowdowns in affected areas, and grey segments indicated impassable infrastructure (flooded underpasses).
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Microsimulation Model: Simulations compared normal traffic flow against emergency conditions, revealing critical nodes, with deteriorating levels of service (LOS) during the flood.
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Actionable Insights
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Analysis of this data allowed us to clearly identify which underpasses are affected by flooding, when these events begin, and how long they last. This is critical for planning escape routes during emergency situations. Knowing exactly which roads are flooded or inaccessible due to bad weather can make all the difference in managing safety during critical events. The analysis highlighted vulnerable infrastructure, offering data-driven solutions to reinforce Palermo’s Road network against future flood events and other emergencies.
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