Modelling flood disruptions to urban transport: A spatio-temporal lens using coupled hydrodynamic–traffic models
Date
2025
Authors
Rebally, Aditya
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Abstract
The transportation sector is an essential pillar of both economic prosperity and social well-being, and its functionality and resilience are increasingly challenged by the impacts of climate change. Transportation systems are directly and indirectly affected by extreme climatic scenarios on a range of spatial and temporal scales, with floods and heavy rainfall being the most critical hazards. In recent decades, urban regions around the globe have experienced notable increases in flood intensity and frequency. Such extreme events can significantly strain transportation networks in the short term through congestion, delays, and trip cancellations; while also producing medium- and long-term impacts associated with infrastructure damage, system recovery, and cascading disruptions that reverberate across economic and social systems.
The present research reviews and advances the understanding of how flooding affects transportation networks across different timescales. Flood effects are classified according to their connection to both the type of flooding and the nature of impact whether direct, indirect, or cascading on the transportation system. Existing literature demonstrates that most studies concentrate on assessing direct and tangible impacts, typically emphasizing short- and medium-term resilience at smaller spatial scales. By contrast, there is relatively limited attention given to indirect or intangible consequences, or to longer-term temporal horizons where recovery, adaptation, and broader socio-economic feedback become more apparent. This imbalance highlights a gap in both methodological approaches and conceptual frameworks, particularly when considering how multiple stressors such as rainfall and flooding interact to magnify disruptions.
To address these gaps, this dissertation applies a combined hydraulic and traffic modeling frameworks to capture the compounded effects of rainfall and flooding on transportation. The 2013 flood in the City of Calgary is selected as the case study considering its severity, dual riverine sources (the Bow and Elbow Rivers), and its well-documented impacts on both urban systems and transportation infrastructure. A hydraulic model (HEC-RAS®) is used to simulate flood dynamics, while a traffic microsimulation model (SUMO®) is employed to replicate traffic conditions under four distinct scenarios: dry/no rainfall baseline, rainfall, flooding with and without rainfall, and post-flooding conditions. Both static and dynamic routing simulations are conducted to compare traveler responses and system performance under varying levels of disruption and adaptability. A new penalty model is proposed that deals with the limitations and enhances the realism of SUMO simulations leading to better quantification of indirect impacts.
Results at the overall network level demonstrate clear degradation of performance across all flood-related scenarios. Compared to the dry baseline, average delay increased by ~165%, average distance travelled grew by almost 49%, and the proportion of lost or uninserted vehicles rose by ~210%, while average speed decreased by ~25%. The rainfall-only scenarios also contributed significantly to these degradations, further exacerbating network inefficiencies by 2 - 17% depending on the performance metric. These findings underscore the importance of considering not only floodwater but also antecedent rainfall conditions when evaluating transportation resilience, as rainfall effects can serve as both precursors to flooding and independent stressors on urban networks. It also demonstrates that indirect impacts can be quantified appropriately when using traffic micro-simulation models.
Beyond aggregated network performance, localized spatial analyses provide further insights. Origin-based assessments reveal zones of vulnerability where the network is less capable of inserting and processing trips, thereby identifying spatial points of systemic weakness. Destination-based assessments, by contrast, highlight the consequences of flooding for accessibility, congestion, and serviceability, demonstrating how certain areas become isolated or disproportionately burdened by disrupted flows. Together, the origin- and destination-based perspectives capture the intertwined nature of vulnerability and congestion, and illustrate how direct, indirect, and cascading impacts manifest unevenly across space and time.
Overall, this dissertation delivers four major contributions: (a) a unified, replicable framework that integrates hydraulic and traffic microsimulation for multi-stage flood and rainfall assessment, (b) a novel penalty model that improves the realism of SUMO outputs for disrupted and congested conditions, (c) a spatio-temporal classification of flood-induced mobility impacts, offering conceptual clarity absent in prior studies, and (d) empirical insights demonstrating how direct, indirect, compound, and cascading disruptions evolve over time and space in a real-world urban network. Collectively, these contributions strengthen the scientific foundation for flood-resilient transportation planning, provide methodological advancements that can be adapted to other cities, and emphasize the importance of multi-hazard, multi-scale mobility analysis under a changing climate.
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Keywords
Temporal scale, Spatial scale, SUMO, Traffic modelling, HEC-RAS, Arc-GIS, Flood modelling, Indirect impacts, Cascading impacts, Flood impacts