NH9.4

Damage modelling generally remains less mature than other components of the flood risk modelling chain. Existing damage models were calibrated for particular regions and flood types, but their transferability to other contexts is scientifically challenging. The calibration of damage models is currently hampered by a lack of reliable empirical data.

In July 2021, devastating floods occurred in several catchments in North-West Europe. Germany and Belgium were particularly hit. This communication presents ongoing initiatives to collect consistent hazard, vulnerability and impact data in the catchment of river Vesdre, Belgium, where up to 30% of annual precipitation was measured in just 48 h. During the night of July 14-15, 2021, the peak discharge in river Vesdre exceeded by a factor 2 to 4 the 100-year flood. At most stations, the observed flow was the highest on record. This led to tremendous tangible and intangible impacts, including 100+ buildings washed out by the flow. Considerable surprise effects also played a part.

A large-scale field survey is being designed to collect, structure and analyse data on flow variables, building characteristics and experienced damage in the housing sector. For the sake of ensuring the quality of data, particularly on technical aspects such as type of building material or level of ground flood compared to street level, a field survey was preferred to an online questionnaire or phone-based interviews.

As an onset for the large-scale flood damage survey, a pilot study was undertaken in November 2021. With the help of a group of students, about 400 buildings were visited to interview the inhabitants. For only 30 % of them, it was possible to get in contact with the inhabitants, as many buildings were still not inhabited due to the extent of the damages. Only for four buildings out of ten, the respondent was willing to conduct the interview, primarily due to lack of time or lack of interest. Other invoked reasons include trauma, language difficulties, or Covid quarantine. It was noticed that building characteristics are easier to obtain when the inhabitant owns the building and that respondents express a strong expectation on receiving feedback on the study outcomes.

Based on collected data, the mean damage per building is 55 k€. However, although the interviews were conducted four months after the event, only half of the participants were able to provide monetary estimates of the damages. The heating system was by far the most affected component due to its usual positioning in the building basements.

The upcoming large-scale survey will enable calibrating suitable flood damage models and provide new insights into damage mechanisms to contribute to improved cost-effectiveness analyses for risk reduction measures.

How to cite: Hardy, J., Roucour, S., Archambeau, P., Erpicum, S., Pirotton, M., Teller, J., Cools, M., and Dewals, B.: Harvesting direct damage data after the July 2021 flash floods in Wallonia, Belgium: a pilot study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3689, https://doi.org/10.5194/egusphere-egu22-3689, 2022.

Coastal flood events generate important damages and economic losses along European coastlines. Flood risk of low-lying areas, where socio-economic activities are in continuous development and the population density is high, will increase due to the anticipated sea—level rise and the climate change-driven alterations in storminess. Therefore, the study and monitoring of coastal flood hazards and impacts are key for coastal risk managers.

At present, the existing coastal-flood databases collect events, mostly at a national level only (e.g., the Spanish Catálogo Nacional de Inundaciones Històricas) or even at Regional Level (e.g. in Italy in Emilia-Romagna the in-storm catalogue), without following a common methodology. Therefore, these databases might lack homogeneity in terms of scope and completeness. In addition, when there is no familiarity with countries’ institutions and agencies providing the resources, it is difficult to collect information by third parties. The news and social media represent possible sources of information, but some quality control should be performed before taking the data into account.

At the European level, there are a few coastal-flooding databases (e.g., MICORE, RISC-KIT, HANZE) but they share common limitations: e.g. they are not regularly updated or they are not publicly available. Considering these weaknesses, as part of the ECFAS Project (EU H2020 GA 101004211, https://www.ecfas.eu/), a new European database has been developed. Through a robust structure and methodology, rather than collecting already processed information, it aims to collect relevant resources of information on past coastal flood events and related impacts, following a standardized classification and providing brief description of the contents of each resource. In this way, the selection of the proper resources and the elaboration of the information therein contained is handed over to the user of the dataset, that will process/filter the information depending on its specific needs.

The ECFAS database of resources provides source information about coastal events that have generated considerable damages and flooding along the European coastlines in the period between 2010 and 2020. These extreme coastal events are linked with specific areas of interest (sites) thereby generating a test case (i.e., a site impacted by an extreme event), which improves the structure of the database since the same storm can hit different areas and the same area can be affected by different storms. The resources of information collected in the database were classified as news, scientific articles, technical reports, institutional websites, or others. For each resource, after a brief analysis, synthetic information were compiled on associated impacts, flood characteristics, hydrodynamics parameters and weather components specifications during the event. The database will be publicly available at the ECFAS webpage and will be distributed as an Excel Workbook. It currently contains 207 resources of information on 26 test cases (defined by 11 coastal events and 27 sites). In the future, new events, test-sites and test-cases can be incorporated as a new event occurs, making the ECFAS database a “living tool”.

How to cite: Souto Ceccon, P. E., Duo, E., Fernàndez Montblanc, T., Montes Pérez, J., Ciavola, P., and Armaroli, C.: A new European coastal storm impact database of resources: the ECFAS effort, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9848, https://doi.org/10.5194/egusphere-egu22-9848, 2022.

How to cite: Modjeska, M., Brémond, P., Grelot, F., Hossard, L., and Graveline, N.: Methodology for assessing flood damage to farms: observation and modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3834, https://doi.org/10.5194/egusphere-egu22-3834, 2022.

How to cite: Brémond, P., Bouche, G., Collard, A. L., Grelot, F., and Tarrit, R.: How does a hidden profession reveal hidden processes and what are the implications for flood damage assessment?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3677, https://doi.org/10.5194/egusphere-egu22-3677, 2022.

Tropical cyclones (TC) and their economic cost risk under climate change are significant concerns globally. Previous studies on TC damage functions and risk assessment are mostly performed based on modelling TC-level damage and thus obtaining annual average loss (AAL) for a country or region. In this study, we used officially released data on reported damage in China to examine patterns of TC damage functions ranging in form and inclusion of risk components, from the county and provincial to TC scale. We find that the robustness of simulated damage increases with spatial scale. Further, TC-induced precipitation tended to be more significant in determining exposure and therefore economic cost of TC, especially at larger scales. Our work provides an empirical assessment of the role of observation scale and damage function in TC economic consequence evaluation and demonstrates that future TC risk at a larger scale may depend on the impact of socioeconomic change.

How to cite: Tang, R. and Wu, J.: Effect of spatial scale on tropical cyclone damage function, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1048, https://doi.org/10.5194/egusphere-egu22-1048, 2022.

Although the impact of floodwaters on buildings is determined by a series of physical mechanisms that, when triggered, result in a wide range of physical damage to buildings and monetary losses, existing research on the topic appears polarized. The majority of work focuses either on the physical mechanisms that transform contact with floodwaters into damage, omitting the estimation of economic consequences, or on improving the estimation of direct damage, but neglecting the mechanisms mentioned above.

In the work we present here, we seek to reconcile these two approaches to investigate the potential implications of both. We begin by considering the exchange of floodwater through the exterior and interior openings of a building to assess direct material damage and estimate the monetary value of the loss. To do this, we build a building-level simulation model by coupling a hydraulic model and an economic model. Our hydraulic model simulates the flow exchanges and the flood water height between the interior and exterior of the building and between the rooms inside the building. The economic model is based on a decomposition of the building into elementary components (wall material, cladding, insulation, floor, furniture, etc.), identifying the room and the height at which they are located. For each elementary component, the damage is modeled for all combinations of water depth and duration of flooding. 

We use our coupled model to simulate four different scenarios on exemplary buildings. The first scenario corresponds to the classical methodology, with homogeneous water depths outside and inside the building. The other three represent: i) street-to-building exchanges in an open plan building; ii) street-to-building/interior exchanges with closed openings; and iii) street-to-building/interior exchanges with open openings. Designating the conventional method as the baseline, we adopt a comparative approach based on monetary valuation of flood damage costs to determine the magnitude of bias of each alternative scenario. Given the high elasticity that flood damage functions exhibit for shallow water depths, the magnitude of the bias in the monetary flood cost assessment for properties may be non-negligible.

The estimates of monetary costs show heterogeneous results. The magnitude of the bias with respect to the reference situation varies from rather modest to non-negligible. This heterogeneity is related to multiple sources: duration and depth of flooding, condition of openings, location of rooms in relation to the entry of floodwater into the building. These results encourage us to carry out additional analyses with buildings having more varied room layouts, but also to take into account the resistance of materials (partitions and openings in particular). They also seem promising to develop a coupled approach to refine the modeling for the estimation of damages, but also to qualify the danger of buildings in case of structural failure.

How to cite: Nortes Martinez, D., Grelot, F., Choley, C., and Finaud-Guyot, P.: Flood impact assessment in urban context: Coupling hydraulic and economic models for a fine scale damage assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3984, https://doi.org/10.5194/egusphere-egu22-3984, 2022.

The European Floods Directive (2007/60/EC) requires that Member States develop flood hazard and risk maps, to be used as the information basis for the development of Flood Risk Management Plans (FRMPs), and to update them every 6 years. To support such a process, the Po River District Authority signed in May 2020 an agreement with 20 Italian Universities and the Italian National Research Council (CNR) with the aim of transferring the state of the art about hydrology (including climate change), hydraulics and damage modelling into the production of the new maps, to be delivered by December 2021. This contribution describes the results obtained by the damage modelling group, composed by 8 universities and the CNR, within the project MOVIDA (MOdello per la Valutazione Integrata del Danno Alluvionale – Model for integrated evaluation of flood damage).
The objective of the project was to provide an Information System able to perform an analytical evaluation and mapping of expected damage, overcoming the limitations of present maps where the evaluation of risk remains highly qualitative and subjective. First, proper exposure and damage assessment tools were identified, for all the categories of exposed elements included in the Directive: population, infrastructures, economic activities (classified as: residential buildings, commercial and industrial activities, and agricultural activities), environmental and cultural heritage, and na-tech sites. These tools address specific requirements: (i) being valid/applicable for the whole District, (ii) being based on standardised and institutional data, available at national level, (iii) being calibrated (and possibly validated) in the Italian context. Second, the dedicated open-source Geographic Information System ISYDE (open-source Information SYstem for Damage Estimation) was developed to support technicians in the implementation of the proposed tools and in the visualisation and processing of damage results. Finally, ISYDE was transferred to Regional Authorities for flood damage evaluation and mapping to all areas at significant risk in the Po District.
Results of damage assessment are collected in dedicated sheets (one for each area) and are presented by means of tables, graphs, and maps, in order to provide both the overall expected damage in a specific area as well as its spatial distribution, for all the five categories of exposed elements. The new developed maps represent a significant improvement with respect to the previous ones, supporting the Cost Benefit Analysis (CBA) of mitigation measures to be defined in FRMPs. Indeed, they enable the identification and localization of typological and spatial hotspots within a single area as well as the comparison among different scenarios, in terms of CBAs.

How to cite: Molinari, D. and Ballio, F. and the MOVIDA group: MOVIDA: a procedure for flood damage assessment and mapping at the river district scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3625, https://doi.org/10.5194/egusphere-egu22-3625, 2022.

How to cite: Balzergue, P., Grelot, F., Meurisse, B., and Guéro, P.: Monetary evaluation of the psychological impacts of floods: Lessons from the application of a French methodology for cost-benefit analysis to the Or catchment area (France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4114, https://doi.org/10.5194/egusphere-egu22-4114, 2022.

The flood event of August 2005 at the river Inn and the actual hazard zone mapping indicated a need for flood protection in the Lower Inn Valley in Tyrol (Austria). To ensure an appropriate protection of settlements, industrial areas and infrastructure up to a return period of 100 years, extensive planning activities for protection and compensation measurements were initiated. In accordance with the Austrian Water Law, a so-called water association was established to bundle decision-making, planning and financing of all protection measurements. The members of the water association are the affected communities and the local operators of infrastructure.
The majority of the cost of flood protection is carried by the federal and state government in Austria. The remaining cost in the Lower Inn Valley has to be divided between the members of the water association.
In order to guarantee a reasonable and fair distribution of costs, as well as voting rights, a specific approach for cost sharing was developed. The allocation of costs and voting rights is based on the protected area and the length of the protected riverbank in the communities. The areas were categorized by actual land use and by the intensity of an expected flood event and weighted respectively in the assessment. Further, the costs for communities were reduced for contributing compensatory measures, such as flood retention space. Operators of infrastructure contribute a fixed share.
In addition to the technical aspects of flood risk management and socio-economic aspects, an essential component in the decision-making is the cost and vote distribution of the affected communities, which thus has far-reaching influence on the entire project.

In this contribution we will detail the fair and specific approach for cost and vote sharing and provide an overview over the process that led to the foundation of the water association. We will report difficulties and the consequences of the chosen approach and give an outlook on the future of the project.

How to cite: Walder, S.: A cost sharing approach to flood risk management decision-making, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4599, https://doi.org/10.5194/egusphere-egu22-4599, 2022.

How to cite: Burns, D. and Oldham, P.: Stepping into the breach: understanding the impacts of defence breach in a UK context, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5639, https://doi.org/10.5194/egusphere-egu22-5639, 2022.

As part of the Bavarian flood protection program 2020plus, a system of controlled flood polders is planned along the Danube River in order to reduce the risk associated with overload flood events and avoid catastrophic flooding. Flood polders work by reducing the maximum discharge during very large flood events, thereby relieving stress on downstream river dikes. Thus, flood polders can effectively contribute to preventing the occurrence of dike breaches.

Since flood polders are expensive to implement, their economic efficiency is investigated using cost-benefit analysis (CBA). The CBA weighs all societal costs against the monetized benefits in the form of an economic efficiency criterion. Different challenges arise in the evaluation. In particular, requirements for data availability and consistency are difficult to meet when evaluating protection measures that are located in and take effect across different agency jurisdictions. Because the CBA has to be conducted within a fixed time frame and budget, it must use models that can work with readily available data. Furthermore, the future effectiveness of flood polders is subject to considerable uncertainty, e.g., concerning return periods of flood events as well as future development of assets, population density and interest rates.

We present a conceptual workflow for CBA of the flood polder program. Its main focus lies on assessing the expected damages, as the reduction thereof is the flood polders’ primary benefit. For this purpose, we perform a comprehensive risk analysis, which involves combining different models for hazard, exposure and vulnerability. The process of hazard analysis is particularly demanding as it includes a catalogue of deterministic flood events routed in a 1D-hydraulic model in combination with a probabilistic dike breach analysis. The large number of hazard areas resulting from different breach locations and characteristics are investigated by means of GIS analysis.

In addition, we highlight the importance of performing sensitivity and uncertainty analysis as part of the evaluation process. This is crucial to address the challenges related to the inherent uncertainties in the occurrence of overload events and future developments as well as model choices, e.g., with regard to model resolution and data sources. We show that the effects of uncertainty on the economic efficiency criterion should be communicated to the decision-makers in order to facilitate robust decisions.

How to cite: Hoffmann, A. and Straub, D.: A conceptual workflow for cost-benefit analysis of flood polders along the Bavarian Danube., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9925, https://doi.org/10.5194/egusphere-egu22-9925, 2022.

Extreme marine storm events have the potential to produce coastal flooding among other hazards. Flood-related impacts are expected to intensify in the future due to climatological factors. Thus, forecasting the impacts generated by marine storms on coastal areas is a key aspect for risk management plans and cost benefit analysis of measures. An integrated approach for the evaluation of coastal flood impacts at the EU scale was developed in the framework of the ECFAS project (EU H2020 GA 101004211), whose main objective is to develop a coastal flood awareness system for the evolution of the Copernicus Emergency Management Service (CEMS).

The approach consists in the integration of literature-based methodologies that were adapted and/or improved to evaluate direct impacts on population, assets (buildings, roads, railways, agriculture, ecosystems, power and nuclear plants) and points of interest. The approach relies on publicly available EU-scale datasets of population, land use/cover, buildings, transport networks, and others. Micro-scale (object-based) and probabilistic methods were applied when data and model availability allowed it, in order to provide a reliable evaluation of the damage and its uncertainty. Otherwise, grid-based exposure methods were used.

A partial validation of the approach was performed by comparing the numerical results with reported qualitative and quantitative information on a few significant extreme events: Xynthia (2010) at La Faute-sur-Mer (France), Xaver (2013) at Norfolk (UK) and Emma (2018) at Cadiz (Spain). At this stage, the impacts were calculated using the LISFLOOD-FP flood maps produced in the framework of the ECFAS project. According to the analysis, this impact approach provides reliable results for the damage to buildings and roads, which represent two of the most important sectors when evaluating flood-related damages. Integrating the ECFAS awareness flood system, this approach will be extensively applied to provide impact results for flood scenarios (1-20 years return period) along the European coastal flood-prone areas.

How to cite: Montes, J., Duo, E., Souto, P., Gastal, V., Grigoriadis, D., Le Gal, M., Fernández-Montblanc, T., Delbour, S., Ieronymidi, E., Armaroli, C., and Ciavola, P.: Evaluating coastal flood impacts at the EU-scale: the ECFAS approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11295, https://doi.org/10.5194/egusphere-egu22-11295, 2022.