Urban flooding: Constructing climate-resilient infrastructure

Àlex de la Cruz Coronas and Patricia Molina López discuss the escalating risks of urban flooding in Europe, highlighting the limitations of traditional flood hazard maps and emphasizing the need for more comprehensive data on the impacts of flooding

Urban flooding is rapidly emerging as one of the most disruptive climate risks faced by Europe’s metropolitan and coastal regions. Intensifying rainfall, sea-level rise, and continued urbanisation are increasing both the frequency and severity of flood events. In densely populated areas, impacts extend far beyond water depths on streets: transport systems stall, energy and water services are disrupted, businesses close, and public safety is compromised. Flood hazard maps alone are no longer sufficient; adaptation requires evidence on who and what is at risk and how severe impacts may be.

In this context, the Horizon Europe projects ICARIA and CLIMEMPOWER, with VEOLIA’s participation, have developed advanced flood models for the Metropolitan Area of Barcelona and the Costa del Sol.

ICARIA: Assessing cascading impacts in metropolitan Barcelona

The Metropolitan Area of Barcelona, home to over three million people, represents one of the most complex urban systems in the western Mediterranean. Flash floods in such environments can trigger cascading disruptions across highly interdependent services. The ICARIA project has applied tailor-made risk assessment methodologies to quantify impacts on specific risk receptors:

Economic damage to buildings and businesses

Direct economic losses are estimated through depth-damage functions based on local building typologies and land uses. Beyond structural damage, business interruption is considered a key component of indirect economic loss. Temporary closure of commercial areas, industrial estates, or logistics hubs can generate substantial secondary impacts that ripple through local supply chains.

Transport disruption and mobility impacts

Urban mobility is particularly sensitive to flooding. In ICARIA, flood impacts on road networks are assessed by combining flood hazard thresholds with traffic- intensity data. Road segments are classified according to their functional importance, distinguishing between local streets and critical corridors. These indicators are essential for emergency planning, as they highlight areas where evacuation routes or emergency response access may be compromised.

Risk to pedestrians and vehicles

Another key study in ICARIA is the assessment of human safety. Flood depth and flow velocity characteristics are translated into hazard categories for pedestrians and vehicles using empirically derived stability criteria. This approach allows identification of areas where flood conditions may pose life-threatening risks, even with limited structural damage. Such information is crucial for early warning systems and public communication strategies.

Critical infrastructure vulnerability

ICARIA also evaluates impacts on electricity distribution, wastewater treatment facilities, waste management services, and other essential assets. The methodology considers both direct impacts and potential chains of cascading effects. For example, flooding of a power substation may disrupt electricity supply to consumers and other infrastructure. By mapping these relationships, the project provides a systemic view of risk, supporting prioritisation of resilience investments where cascading effects are most likely.

CLIMEMPOWER: compound risk and coastal exposure on the Costa del Sol

In Costa del Sol, rapid urban development, high seasonal population peaks, and coastal exposure combine to create a complex scenario. In this context, CLIMEMPOWER focuses on compound flooding scenarios, where multiple drivers interact and amplify impacts.

CLIMEMPOWER advances the state of the art in flood risk assessment by developing a large-scale, coupled modelling framework that integrates urban 1D/2D sewer and surface runoff models with coastal hydrodynamic simulations. The approach enables the explicit representation of compound flooding mechanisms in urban coastal environments, including the interactions among intense rainfall, sewer surcharge, surface flooding, and sea level variability. Particular attention is given to data heterogeneity and scarcity, which are common limitations in real-world applications. To address this, innovative gap-filling methodologies are applied, combining open datasets, stakeholder-provided information, and inference techniques to ensure robust model performance even in data-constrained contexts.

Beyond hazard estimation, the project moves towards a more comprehensive evaluation of flood risk by analysing impacts on multiple receptors, with a strong focus on critical infrastructure and sensitive environmental areas. Advanced climate data analysis and multivariate approaches are employed to characterise current and future compound flood scenarios, incorporating updated Intensity–Duration–Frequency relationships and climate projections aligned with the latest IPCC assessments. This allows for assessing how climate change may alter the frequency and severity of compound flooding and its cascading impacts.

A transferable approach for European regions

While Metropolitan Area of Barcelona and the Costa del Sol provide contrasting case studies, the impact assessment methodologies developed in ICARIA and CLIMEMPOWER are inherently transferable.

Across Europe, urban and coastal regions face similar challenges: ageing infrastructure, increasing exposure, and climate-driven intensification of extreme events. The structured integration of economic loss estimation, safety risk assessment, and critical infrastructure analysis offers a robust guide for other territories.

Importantly, the approach is adaptable to different data environments and governance contexts. It allows authorities to progressively refine risk assessments as new information becomes available, thereby supporting iterative, evidence-based adaptation.

Within ICARIA, full risk assessments considering a large set of hazards, multi-hazard drivers, and risk receptors have been performed. The methodologies enabling these comprehensive assessments are grounded in the deep sectoral expertise of VEOLIA. A significant part of this knowledge has been translated into an open, web-based Decision Support System tool. Although lacking the exhaustive depth of the offline risk assessments used in the original case studies, it still allows for effective damage evaluation without requiring the same level of prior expert knowledge or detailed offline analysis.

Strengthening resilience through integrated risk analysis

ICARIA and CLIMEMPOWER demonstrate that effective flood risk management requires more than understanding where water will flow. It requires a detailed appreciation of how floods affect people, services, and economies – and how those impacts may evolve under climate change.

Through tailored, multi-sectoral impact assessment frameworks, VEOLIA has helped transform complex hydrodynamic simulations into actionable intelligence. By quantifying risks to pedestrians and vehicles, estimating economic losses, and mapping vulnerabilities across critical infrastructure networks, the projects provide a solid technical foundation for climate-resilient urban planning.