Session B5 - Planning and management of urban flood risk

Extreme precipitation events and the resulting pluvial flooding are expected to become more frequent and more intense in the future. Advanced and fast flood modelling is therefore indispensable. However, to properly assess the performance and reliability of flood models, robust validation is essential. Validation data, such as surface water level measurements, are rare, often incomplete, or entirely absent. Consequently, there is a growing shift toward the use of unconventional data sources. This study investigates the potential of fire station operational data as a validation source for the Dynamic CA-ffé fast flood modelling approach across three Austrian case studies: Innsbruck, Kufstein, and Feldbach. The validation based on operational records focuses on identifying affected buildings and comparing flood extent with photos from real events. Additionally, a reference validation of affected buildings was conducted using a coupled 1D/2D SWMM model. The results show that although fire station records allow comparisons only for documented affected buildings, they still provide a reliable indication of the general flood situation. Hit rates on affected buildings range from 34% to 89%, depending on the precipitation event and case study and also fit with the hit rates in the 1D/2D reference model. Overall, fire brigade operational data can be considered useful for coarse validation of urban flood models. However, more definitive conclusions require expanding data collection to include non-reported flooded buildings, unaffected buildings, water level information, and more extensive photographic documentation.

Flood risk management is characterised by its complexity, involving multiple institutions, expertise, databases, logistics and governance. From planning and preparedness to emergency management, the spatial and temporal scales of action are usually quite different, requiring sound coordination between policies and institutions. In this process, pertinent and good-quality hydrological information is of high relevance. Nevertheless, particularly in cities of developing countries, mismatches are observed between the availability and quality of hydrological information and its use in the several phases of flood management planning and implementation, frequently compromising its effectiveness. Effective flood risk management becomes more relevant in face of climate change, since in many regions in the world increases in rainfall intensity and in the frequency of extreme events are expected, combined with heat waves and water scarcity. In the present paper, we address these issues considering four case studies in Brazil, the cities of Belo Horizonte, Brasília, Recife, and Curitiba. All these cities have implemented innovative approaches to flood risk management, covering the different phases of the management process. In the conclusions, we identify needs and potential ways for the improvement of flood management in the context of cities which exemplify challenges for flood management in the developing world.

Urban development and climate change are amplifying the risk of pluvial flooding (surface runoff), which is still poorly taken into account in planning even though it represents a growing share of flood-related damages. Hydrogeomorphological (HGM) mapping of runoff approaches this risk through landforms and the natural dynamics of catchments, including in highly urbanised contexts. The method combines automated pre-processing of accumulation zones (calculation of flow paths and topographic depressions) with expert interpretation, systematically ground-truthed in the field with municipalities. When introduced upstream in Stormwater Management Master Plans, HGM mapping provides an evidence base for identifying hydraulic “black spots”, showing that many recurrent network overflows coincide with areas of concentrated or diffuse runoff. Beyond the risk dimension, these maps become a support for urban renaturation: crossed with indicators of tree canopy, urban overheating or potential for de-sealing, they highlight “water pathways” where the water cycle can be restored and spaces of coolness, biodiversity and landscape quality can be created. The communication will present the methodological approach, feedback from several local authorities in southern France, and avenues for integrating HGM runoff mapping into an urban renaturation strategy that places water at the heart of the territorial project.