NH9.4

NH9 EDI
Costs of Natural Hazards 

Assessing the costs of the overall economic impacts of natural hazards, costs of prevention and costs of responses to natural hazards supply crucial information for decision-making practices in the fields of disaster risk reduction, natural hazard and risk management and climate change adaptation planning. However, the lack of empirical impact data as well as the significant diversity in methods that are currently applied in costs assessments of different natural hazards and impacted sectors make it difficult to establish comprehensive, robust and reliable cost figures. This also hinders comparisons of associated costs across countries, hazards and impacted sectors. This session aims to review current methodological approaches for assessing individual cost types (such as direct damages to housing, indirect losses, as well as costs of risk reduction) and aims to show how these methods are used in the context of various natural hazards (e.g. floods, droughts, earthquakes).

We welcome submissions in the areas of assessing these various types of damage induced by any kind of natural hazard. Also, we are interested in contributions that focus on the cost-effectiveness or efficiency of risk reduction to natural hazards and adaptation to increasing weather risks that are due to climate change. Presentations are welcome for instance on model development, validation, uncertainty analysis, risk assessment frameworks as well as presentations about the application of damage models in case studies. Abstracts are sought from those involved in both the theoretical and practical aspects related to these topics.

Excellent submissions which are deemed important contributions to the session will be classified as “solicited talks”.

Convener: Nivedita SairamECSECS | Co-conveners: Veit BlauhutECSECS, Pauline Bremond, Viktor RözerECSECS, Heidi Kreibich
Presentations
| Fri, 27 May, 11:05–11:46 (CEST), 13:20–14:47 (CEST)
 
Room 1.61/62

Presentations: Fri, 27 May | Room 1.61/62

Chairpersons: Pauline Bremond, Viktor Rözer
11:05–11:08
around data collection
11:08–11:18
|
EGU22-3689
|
ECS
|
solicited
|
Virtual presentation
Joris Hardy, Solène Roucour, Pierre Archambeau, Sébastien Erpicum, Michel Pirotton, Jacques Teller, Mario Cools, and Benjamin Dewals

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.

11:18–11:25
|
EGU22-7021
|
Highlight
|
Virtual presentation
Sonja Szymczak, Fabia Backendorf, Veit Blauhut, Frederick Bott, Katharina Fricke, Thomas Junghänel, and Ewelina Walawender

Heavy precipitation events are an important trigger for flash floods and landslides on local and regional scale. In contrast to river floods, the enormous erosion potential in catchment areas contributes significantly to the extent of damage of infrastructure located in the valley floors. Due to the mobilisation of large amounts of sediment and deadwood, entrapment occurs at narrow points, e.g. bridges, which can subsequently lead to high flash flood waves, leading to destruction of transport infrastructure located close to rivers and streams. Considering climate change, such events are supposed to increase in the future. Hence, there is an urgent need to increase traffic resilience to this hazard.

This contribution examines the impact of the heavy precipitation event from 14./15. July 2021 on the railway in the Ahr valley in Rhineland-Palatinate, Germany. Large parts of the railway infrastructure were completely destroyed by the flood event. In a first step, a detailed overview of the climatological and hydrological drivers, by means of spatially high-resoluted distribution of precipitation and peak discharges modelling, is given. The event is than compared to past flash flood events of 1910 and 2016 along the Ahr valley. The second step presents a detailed mapping of the damage that occurred along the railway line based on aerial photographs, and addresses the question of the extent to which the railway infrastructure, especially bridges, contributed to the increase in the flood wave and the erosion potential. Based on the analysis, recommendations for action to foster the resilience of railway infrastructure to flash floods are presented, especially the question what magnitudes and return periods of events future dimensioning of railway infrastructure should be based on.

How to cite: Szymczak, S., Backendorf, F., Blauhut, V., Bott, F., Fricke, K., Junghänel, T., and Walawender, E.: Impacts of heavy and persistent precipitation on railway infrastructure – insights from the Ahr valley, Germany July 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7021, https://doi.org/10.5194/egusphere-egu22-7021, 2022.

11:25–11:32
|
EGU22-12012
|
ECS
|
Virtual presentation
Bernard S. Majani, Bruce D Malamud, and James Millington

Many urban areas in the Global South are often data-poor and lacking in longer-term records of the occurrence and impact of natural hazards. Here we explore a methodology for using blended evidence sources to build a history of flooding impacts, along with a hazard severity scale, in Nairobi, Kenya, from 1978 to 2018. The evidence we use to build our Nairobi Flood Impact Database includes existing digital flood databases, newspapers, radio/TV broadcasts, government and NGO reports, peer-review journal articles, insurance company and emergency service records, online website reports, blogs, Google Analytic records and 330 photos/video from social media sources. For each record, we systematically extract from the source material, available information on the flood’s location, timing, and impact, with impact broken up into human (7 subcategories, e.g., fatalities), infrastructure (18 subcategories, e.g., building damage) and environment (6 subcategories, e.g., trees fallen). The resultant Flood Impact database has 1495 entries, which when entries that refer to the same flood event are grouped, result in a total of 354 flood events for 1978 to 2018 (41 years) in Nairobi, a much more extensive record than available previously. The flood database has the largest number of records for 2011 to 2018, given the increased use of social media and newspapers to report flood event impacts in recent years. We also see a peak in the years 1996 to 2000 (when there was a particularly heavy amount of rain due to El Niño) and then again 2016 to 2018. We then develop a five-point Likert scale for evaluating the adequacy of evidence types for recording location, timing and impact of floods. Finally, using a combination of existing impact-related natural hazard scales from the literature and our database, we build a five-part flood severity index combining the different types of impact, ranging from minor to catastrophic floods. Each of the impact types (31 subcategories) from our impact database is given a weighting from which inform this five-point severity index and map this severity index onto selected flood events from our Nairobi Flood Impact Database. Our database was then examined for temporal and spatial clustering in Nairobi and compared to different types of urban built up areas within Nairobi. This research provides a methodology and extensive blended database of the impact of floods over a 41-year period in a data poor area, providing a resource for better understanding the past history of spatial temporal hazard patterns, which can then be further expanded as to the causes, impact and how the flood events were dealt with in terms of recovery, lessons learnt and ways of mitigation and resilience building.

How to cite: S. Majani, B., D Malamud, B., and Millington, J.: Use of blended evidence sources to build a history of flooding impact and an impact severity scale: A case study of Nairobi, Kenya, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12012, https://doi.org/10.5194/egusphere-egu22-12012, 2022.

11:32–11:39
|
EGU22-9848
|
ECS
|
Highlight
|
Virtual presentation
Paola Emilia Souto Ceccon, Enrico Duo, Tomàs Fernàndez Montblanc, Juan Montes Pérez, Paolo Ciavola, and Clara Armaroli

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.

11:39–11:46
|
EGU22-7833
|
ECS
|
On-site presentation
Max Steinhausen, Martin Drews, Morten A. D. Larsen, Levente Huszti, and Kai Schröter

Pluvial floods present an increasing risk in urban environments all over the world. High-resolution, state-of-the-art pluvial flood risk assessments are urgently needed to inform disaster risk reduction measures and climate change adaptation. Still, pluvial flood risk models are generally not empirically tested because of the rarity of local high-intensity precipitation events and/or lack of monitoring and reporting capabilities.

With a combination of Volunteered Geographic Information (VGI) and insurance claims data, we test the validity of hazard, exposure, and multiple vulnerability components of a pluvial flood risk model. As background for our research, we use the city of Budapest, which suffered three heavy rainfall events associated with significant flood damages in just five years (2015, 2017 and 2020). For each pluvial flood event, we collected photographic evidence of flooding from different online media sources, as well as claims data from the Association of Hungarian Insurance Companies (MABISZ) for residential buildings.

Based on the context information shown in the photos, we identified their location in the city through comparison with Google Street View imagery and estimated the associated water depths. These were compared with the results of a generic-type pluvial flood model. The estimation of flood losses revealed spatial patterns of pluvial flood risk in Budapest. We tested the loss estimates against reported loss in the 23 districts of Budapest to better understand the reliability and accuracy of pluvial loss models.

In general, our findings highlight the untapped potential, but also reveal important challenges in using VGI for model evaluation. It is proposed that VGI are used more systematically to improve the confidence in model-based risk assessments for climate change adaptation and disaster risk reduction.

 

How to cite: Steinhausen, M., Drews, M., Larsen, M. A. D., Huszti, L., and Schröter, K.: Testing the validity of pluvial flood risk models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7833, https://doi.org/10.5194/egusphere-egu22-7833, 2022.

Lunch break
Chairpersons: Heidi Kreibich, Veit Blauhut, Pauline Bremond
13:20–13:27
|
EGU22-11423
|
ECS
|
Virtual presentation
Iolanda Borzì, Andrea Magnini, Beatrice Monteleone, Riccardo Giusti, Natasha Petruccelli, Ludovica Marinelli, Marcello Arosio, Alessio Domeneghetti, Attilio Castellarin, and Mario Martina

The estimation of flood damage plays a key role for planning and implementing flood risk prevention and mitigation measures. While many contributions can be found in the scientific literature about inundation damage to buildings and infrastructures, estimation of losses to the agricultural sector is currently poorly discussed. Even if different conceptual or physically based models have been proposed for the agricultural sector as well, studies testing their application to real cases are still not sufficiently abundant due to the difficulties in finding appropriate inundation and damage data. The present work attempts to contribute in this matter by investigating the impacts of a recent inundation event: the selected case study is the flood event occurred the 6th December 2020 in Northern Italy (Emilia-Romagna region), caused by the formation of a breach on the right levee of the Panaro River. The area is mainly devoted to agriculture, with farmers growing prevalently winter wheat, sorghum and forage crops, such as alfalfa. The inundation footprint has been reproduced by means of a detailed 2D hydraulic model settled with HEC-RAS software (v. 6.0). The model focuses on the accurate reproduction of water depth and permanence required for the estimation of damages to agriculture activities. Model validation refers to different observed data: (a) inundation extent, (b) maximum water depth and (c) duration of water presence; data has been collected from various sources: remote sensing images, surveys to local land owners and interviews to authorities involved in the inundation management. Although representative of a preliminary investigation, the study provides additional insights towards a better estimation of potential impacts of inundation events on agriculture activities.

How to cite: Borzì, I., Magnini, A., Monteleone, B., Giusti, R., Petruccelli, N., Marinelli, L., Arosio, M., Domeneghetti, A., Castellarin, A., and Martina, M.: Inundation Impacts on Agriculture: Reconstruction and Preliminary Findings of the Recent Event occurred along the Panaro River, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11423, https://doi.org/10.5194/egusphere-egu22-11423, 2022.

13:27–13:34
|
EGU22-3834
|
Virtual presentation
Maxime Modjeska, Pauline Brémond, Frédéric Grelot, Laure Hossard, and Nina Graveline
In the context of climate change and growing urbanization, farms are expected to face more frequent extreme events (e.g. heat peaks, droughts, frost, hail or floods). Floods being the natural hazard that generates the most damage in the world, we focus our research on the impact of floods on farms and their adaptation to climate change. Flood damage on farms is the result of complex phenomena involving biophysical processes on the one hand, and farmers' decisions on rehabilitation and adaptation on the other. Some impacts are directly visible; others may be delayed and persist over time (Bremond et al, 2013). When they persist over time, they may impact the development trajectory of farms.
For the observation of impacts, there are in fact two challenges: to identify the diversity of impacts and their temporality of occurrence. Field surveys following flood events often focus on short-term damage and on impacts resulting from extreme events, leaving long-term damage and minor events aside. In this paper, we aim to propose a methodology that we are currently implementing to jointly and recursively improve the observation and modelling of flood impacts on agricultural systems. In particular, we wish to define more precisely the diversity of flood impacts and long-term damage on farms by taking into account the development trajectory of farms. To this end, we combine two complementary approaches: observation and modelling.
Our work is implemented in the framework of the system of observations of the impacts of floods (so-ii, http://so-ii.org), in the Greater Montpellier area, coordinated by our team. Based on our experience, we have developed diverse methods for both short-term and long-term monitoring such as: surveys, participative workshops, drone pictures, predictive models. 
To cover on field-observations, quantitative and qualitative surveys have been carried out over the years on the so-ii territory. Interviews took place both after a flood, to gather quantitative data, and several years after a flood (Bremond et al, 2020), to collect quantitative and qualitative data. In parallel, we are exploring the use of drones to gather pictures of plots from post-flood to several years later in order to understand mechanisms behind the impacts of floods on soil, plant material and adaptations. To reinforce long-term monitoring, we have set up a network of impact observers, on the so-ii territory, with whom we agreed to work over the long-term (about fifteen years).
On the other hand, we are working on the use of predictive models to estimate flood damage to farms. For now, 3 models have been developed: floodam.agri (Bremond et al, 2022), R-EVA (Bremond et al, 2012) and COOPER (Nortes Martinez et al, 2021). Each of these models have different application levels (respectively plot, farm and cooperative system) and time-scales which helps for the observation of farm trajectories as a whole.
In conclusion, we will discuss the perspectives and limitations of this approach. We will open up on the perspectives to share our methodology so it can be adapted to other territories by stakeholders who are interested in setting up a similar system of observation.

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.

around damage models
13:34–13:41
|
EGU22-1037
|
ECS
|
On-site presentation
Aishwarya Narendr, Shantanu Anand, Bharath Haridas Aithal, and Sutapa Das

The study aims to investigate flood-related damage on earthen buildings using an experimental analysis. Wattle and daub method is the main construction technique used in the coastal part of West Bengal, India. Housing damage caused due to floods is often poorly compensated due to the absence of an established loss-assessment scale for vernacular housing typologies a predominant construction practice in the study region. Earthen buildings developed using various techniques have proven functional, while offering multiple benefits such as cost and energy efficiency along with thermal comfort. Despite the benefits, the functionality gets significantly reduced due to their susceptibility to flooding instances that are likely to increase with aggravating extremes as a result of changing climate. The contribution of vernacular or traditional construction techniques if integrated with disaster resilience techniques shall prove indispensable in reducing the shortage of 29.6 million dwelling units for the low-income rural households by the year 2022 in the study region.

The qualitative assessment of the damage process involves visual inspection of the sealed model of the building component behaviour and a non-destructive test. Under the qualitative process, the sample is tested under Universal Testing Machine (UTM) machine to understand the loss of compressive strength at each stage of flooding. The process will result in a damaged matrix which is an array of loss percent for various depth–duration combinations. The matrix will help in identifying corresponding flood losses and deciding repair costs for varying flood intensity. In addition to this, the process can be identified as an imperative step while suggesting an alternate construction technique in such a flood-affected region.

Keywords: Flood damage,Vernacular housing, Damage matrix, Non-destructive tests, Destructive tests

How to cite: Narendr, A., Anand, S., Haridas Aithal, B., and Das, S.: An experimental approach for developing a building damage matrix for the flood-affected vernacular housing typology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1037, https://doi.org/10.5194/egusphere-egu22-1037, 2022.

13:41–13:48
|
EGU22-3677
|
Virtual presentation
Pauline Brémond, Guillaume Bouche, Anne Laure Collard, Frédéric Grelot, and Reine Tarrit
Flood economic damage results from complex phenomena involving biophysical processes that determine the damage of the components but also the decisions taken for reconstruction. The method most frequently used to estimate damage is based on the assumption that the property will be restored to its original condition. This method is supported by expert knowledge of damage processes and restoration costs. However, in practice, we wonder about the implementation by individuals of this identical restoration at a time when the build back better is an injunction that is found in many institutional discourses. In France, insurance experts are mandated by insurance companies within the framework of the cat-nat insurance process to ascertain and evaluate the damage suffered by insured persons following a flood. This experience gives them a privileged place to feed the ex ante damage assessment models.
However, although, the experts intervene to establish the damage at the very moment when the dwellings are dealing with reconstruction decisions, this profession remains little studied in the literature. In this study, we tried to determine, on the one hand, to what extent the posture of experts influences the assessment of damage and, on the other hand, what role they play in the process of reconstruction and individual adaptation of housing following a flood.
Since 2012, we have met with 15 insurance experts, conducted 20 individual interviews and two intermediate workshops on understanding damage mechanisms and estimating repair costs. This work has enabled us to develop damage functions for different sectors (households and economic activities) which were validated during a participatory workshop with the experts. We will present a critical analysis of this work, focusing on the view of damage held by insurance experts and the underlying assumptions. To complete this analysis, we have carried out additional work specifically on the role of insurance experts in the reconstruction process of households. Through a qualitative field survey in 2021, we met a dozen insurance experts. First, we established the standard expertise process used by the experts. Based on these procedures, we questioned them on how to conduct an expertise. Through narratives, we highlighted the roles that insurance experts actually play with dwellings. In particular, we showed that despite the technical and human skills available to the experts, the issue of reconstruction can only be dealt with informally and remains marginal due to the missions entrusted to the experts by the insurance companies. In conclusion, we will discuss the implication for damage estimation.

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.

13:48–13:55
|
EGU22-1048
|
Virtual presentation
Rumei Tang and Jidong Wu

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.

13:55–14:02
|
EGU22-3984
|
ECS
|
Virtual presentation
David Nortes Martinez, Frédéric Grelot, Cécile Choley, and Pascal Finaud-Guyot

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.

around the use of cost assessement
14:02–14:09
|
EGU22-3625
|
Highlight
|
Virtual presentation
Daniela Molinari and Francesco Ballio and the MOVIDA group

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.

14:09–14:16
|
EGU22-4114
|
Virtual presentation
Pierre Balzergue, Frédéric Grelot, Bénédicte Meurisse, and Paul Guéro
The implementation of hydraulic development projects in flood risk prevention policies is based, in France as in many other countries, on a cost-benefit analysis to justify the efficiency of the projects. The methodology of this type of analysis, following the recommendations of the French government, currently only includes the monetary evaluation of material damage. However, numerous post-flood field surveys show that inhabitants can be strongly impacted psychologically even when they are flooded at a low level. It is important to take into account these impacts, such as post-traumatic stress disorder, depression, etc., as they can result in significant costs such as medical expenses, inability to work or pursue domestic or leisure activities, loss of well-being, etc. However, their assessment is difficult as there is currently little empirical data on the psychological damage of flood-affected populations.
 
In order to improve the scope of the indicators of the cost-benefit analysis, various experts on post-flood health impacts, on monetary valuation of health effects and on socio-economic evaluation of flood management projects have been mobilised by the French State. Based on an analysis of the international literature and the expertise of the people called upon, a methodology for the monetary estimation of psychological impacts was produced.
It was designed to be operational, i.e. usable by any project developer in France. This methodology only takes into account post-traumatic stress disorder (PTSD), which is the main psychological damage in the event of flooding. The damage is calculated according to the level of exposure of the inhabitants during each flood scenario, with, for single-storey dwellings, a threshold corresponding to a water height of more or less 1 metre in the dwelling. Different levels of exposure are then assigned a probability of post-traumatic stress disorder as defined in the meta-analysis by Chen et al, 2015. Finally, an average cost of PTSD to the community was defined.
This methodology was then applied to five contiguous case studies in the Or basin (Hérault department, France), where hydraulic projects and cost-benefit analyses had been carried out in 2016. This application shows that taking into account psychological damages compared to other material damages has a very variable effect depending on the case. Moreover, the values of the calculated psychological damages are not directly anticipable in relation to housing damages. Indeed, a dwelling may be less damaged by the project without removing its inhabitants from the floodplain.
 
Finally, the results of this study show the interest of integrating this method of psychological damage assessment in the cost-benefit analysis of projects.
Thus, depending on the nature of the projects, taking into account the psychological impacts can significantly reinforce the interest of a project or, on the contrary, only add a very marginal benefit. We also show under what conditions it can be effectively applied (what data is needed), with a view to anticipating its possible use in non-French contexts.

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.

14:16–14:23
|
EGU22-4599
|
Highlight
|
Virtual presentation
Stefan Walder

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.

14:23–14:30
|
EGU22-5639
|
ECS
|
On-site presentation
Douglas Burns and Phil Oldham

Flood defences help mitigate the impacts of flooding on people, properties, and infrastructure. In JBA’s catastrophe flood model for the UK, defences are included to help estimate flood losses for re/insurers. It is important that these defences operate properly, although there is some uncertainty whether defences will continue to offer protection to properties if their condition deteriorates or a flood event reaches a loading greater than a defence was designed to mitigate against. The breach of a defence drastically increases losses to properties local to the point of breach, and representing this in a catastrophe model can help re/insurers better understand the impact defences can have on losses.  

The Environment Agency publish fragility curve data for different types of defence structures, condition grades, and breach mechanisms which estimate the probability of a flood defence failing. Using these data in the catastrophe flood model as part of a probabilistic defence breach algorithm shows that the uncalibrated fragility curves vastly over-estimate the likelihood of defences breaching in the UK, where the condition of defences is generally good and investment is strong. Calibration of the fragility curves is required to accurately reflect the observed rate of breaches given the maintenance regime in the UK. Catastrophe models which have not been calibrated to match observed breach rates could over-estimate loss, this finding is supported by previous research funded by the JBA Trust which concluded the breach rate was being overstated in the NaFRA. We investigate the effect of defence breach in our catastrophe model. 

JBA has developed an ultra-flexible approach to catastrophe modelling, which enables “what if” type questions to be easily answered. Models are configured, built and executed, all at run-time. The modularity inherent in our catastrophe model means that the development and integration of a probabilistic defence breach algorithm is quick and straightforward. The parameterisation of the model makes it simple to select from interchangeable methods, swap input data sources and to set the value of variables. This paradigm is ideally suited for calibrating defence breach parameters and for running different defence breach scenarios effectively. 

By comparing losses modelled with uncalibrated and calibrated defence breach probabilities, we quantify the potential over-estimation of loss when using the input fragility curve data in its published form. In the UK we have relative wealth of information to work with, however defence fragility and breach rates around the world are not well understood and emphasis should be put on the benefits of collecting data to help accurately quantify the effect of proper maintenance and to achieve accurate loss estimates.   

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.

14:30–14:37
|
EGU22-9925
|
ECS
|
Virtual presentation
Amelie Hoffmann and Daniel Straub

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.

14:37–14:47
|
EGU22-11295
|
ECS
|
solicited
|
Virtual presentation
Juan Montes, Enrico Duo, Paola Souto, Véra Gastal, Dionysis Grigoriadis, Marine Le Gal, Tomás Fernández-Montblanc, Sebastien Delbour, Emmanouela Ieronymidi, Clara Armaroli, and Paolo Ciavola

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.