Flood risk assessment in vulnerable areas is crucial for efficient flood risk management, including the analysis and design of civil protection measures and the implementation of studies with proper interventions towards mitigating flood risk. This is even more crucial in highly dense urban river basins such as the ones in the region of Attica, which is hosting Athens, the capital of Greece, as well as critical infrastructures and important social economic activities. In the framework of the Programming Agreement with the Prefecture of Attica, the Operational Unit BEYOND Centre of EO Research and Satellite Remote Sensing of the Institute of Astronomy, Astrophysics, Space Applications & Remote Sensing (IAASARS) of the National Observatory of Athens (NOA), in cooperation with the Research Group ITIA of the Department of Water Resources and Environmental Engineering of the School of Civil Engineering of the National Technical University of Athens (NTUA), study five flood-stricken river basins in the region of Attica, which affect 23 Municipalities. The research teams collect all available data, conduct detailed field visits, run hydrological and hydraulic models, and assess flood hazard, flood vulnerability and eventually flood risk in every area of interest. Furthermore, high-risk critical points are identified, and mitigation measures are proposed, both structural and non-structural, in order to achieve effective crisis management for the protection of the population, the properties and the infrastructures. In addition, the BEYOND Centre has developed a web GIS platform where all the collected and produced data, the flood hazard, vulnerability and risk maps, as well as the identified critical points, the refuge areas and escape routes are stored and made available. All the relevant stakeholders and the competent authorities, who are directly or indirectly involved in civil protection, participate in dedicated workshops designed for their needs, and moreover, the studies’ general outcomes are disseminated to the wider public for raising awareness purposes. The response of the end users is very positive, and their feedback very constructive. The methodology and the outputs of the project are in line with the requirements for the implementation of the EU Floods Directive 2007/60/EC, the Sendai Framework for Disaster Risk Reduction, the UN SDGs, as well as the GEO’s Societal Benefit Areas.

How to cite: Tsouni, A., Sigourou, S., Dimitriadis, P., Pagana, V., Iliopoulou, T., Sargentis, G.-F., Ioannidis, R., Chardavellas, E., Dimitrakopoulou, D., Mamasis, N., Koutsoyiannis, D., and Kontoes, C. (.: Multi-parameter flood risk assessment towards efficient flood management in highly dense urban river basins in the Region of Attica, Greece, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12624, https://doi.org/10.5194/egusphere-egu23-12624, 2023.

A city-wide approach to reduce the uncertainty regarding the spatial variability of urban flooding events is required in urban catchments. The goal of this study is the development of a modelling framework independent of the spatial scale to address the most hazardous areas in the current state and the future. The framework starts with the definition of the study objectives (e.g. reducing flood risk), which have a direct impact on the spatial and temporal scale, the used model approach, the data requirement and the level of detail. Furthermore, potentially hazardous areas will be identified with the potential flood risk index (PFRI_i). The determination of this is a risk-based approach (R=E*V*H) which combines the exposition (E) with the vulnerability (V) and the hazard (H). The population density of each object and the total number of persons in the catchment will quantify the exposition. The vulnerability includes the number of past damage events and the object use. How accurate the modelled hazard is considered, depends on the used model approach: i) GIS-based; ii) only 1D; iii) only 2D; iv) 1D/2D models. The combination of H and V resulted in the risk factor (RF_i) in four levels of detail depending on the used model approach. This allows both, the quantification of hazardous areas at the current state and the change of the PFRI_i by future scenarios such as climate change and urbanization.

PFRI_i = n_P,k * RF_i / (A_k * ∑P)                                                                                                                                                                                     

PFRI_i=Potential Flood Risk Index; n_P,k= number of Persons on a private ground k; A_k=total object area; =total number of persons in the catchment; Rf_i= risk factor depending on the used model approach k

The GIS-based flow path analysis as the first level of detail can be used to identify the urban flooding hot spots. This allows the identification of hazardous sub-catchments in a city or high-risk private ground in a catchment quantified by the PFRI_GIS. This is useful for further detailed analysis with other model approaches (e.g. 1D/2D model). The next steps are the implementation of the demonstrated framework for each level of detail in the city of Graz in Austria. Furthermore, the framework will integrate different climate scenarios based on a high-resolution climate model to address the impact of climate change on the urban drainage system quantified by the PFRI_i.

Keywords: urban flooding, urban flood modelling, risk assessment, future changes

How to cite: Reinstaller, S., König, A., and Muschalla, D.: A modelling framework to assess urban flood risk on the city scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7707, https://doi.org/10.5194/egusphere-egu23-7707, 2023.

This research develops a methodology to examine the change over time of urban textures for Nairobi in relation to flood hazard impact on infrastructure. We use three Landsat 7 (30 m resolution) images of Nairobi (2008, 2013, 2018). ‘Urban textures’ are the spatial distribution, shape and relative arrangement of urban elements such as green spaces, trees, roads and height of buildings and their geometry in a given urban city. Here, revising Stewart and Oke’s classifications for built-up areas and land cover types, we classify each of the three Landsat images into 14 urban textures using maximum likelihood under supervised classification. The building structure types were then examined using local knowledge, YouTube videos, Google Street View and ground truthing. We find that from 2008 to 2018 the urban textures with the largest total increases in area were compact mid-rise by 49.9km2 (6.9%) and compact high-rise by 11.3 km2 (1.5%). In contrast, the compact low-rise residential urban texture decreased greatly (29.2 km2). This suggests that for non-industrial land uses, Nairobi has grown upward. Accuracy assessments for the 2008 [2018] map were 83.6% [87.9%] with 95% confidence interval of 75.4–90.0% [80.6–93.2%] and kappa statistic 0.777 [0.834]. We then examine the spatial temporal change of intensive (high severity – low frequency) and extensive (low severity – high frequency) flood hazard events in terms of pattern, trend and impact in relation to rainfall, elevation, and urban textures. We find that urban textures for 2018 have reduced area coverage of the urban texture lightweight low-rise, having partly changed to compact midrise. The impact of change in land use through the development of urban areas greatly affects flooding and impacts in terms of severity. Flooding is more prevalent close to the major rivers in Nairobi, some of which occur in the non-informal settlements. Flood water flows from the higher areas of Ngong and Kikuyu towards the town centre, Nairobi west into industrial area going towards east lands. Rivers in Nairobi regularly overflow their banks and inundate low-lying areas like T-Mall, Nairobi west, industrial area and Mathare valley. These are the flood hotspots of Nairobi that also have high severity of fatalities and impact on infrastructure. We believe that our methodology of examining urban textures over time, using remote sensing images, combined with flood hazard impact information, will help scientists and hazard managers better understand, and prepare for, the interlinked nature of urban change with the flood hazard.

How to cite: Majani, B., Malamud, B. D., and Millington, J.: Urban textures and flood hazard impacts from 2008 to 2018 in Nairobi, Kenya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17553, https://doi.org/10.5194/egusphere-egu23-17553, 2023.

Urban flooding occurs to  populated and build environments when there is excess water due to intense rainfall, extreme river flows, or storm occurance. Flood protection procedures and processes are  important and critical tools in flood-vulnerable and flood-prone areas. The consequences of the occurrence of such phenomena can have a seriously negative impact on a social, economic and environmental level. The first two categories are particularly affected in urban environments, where flooding might lead to severe casualties. The assessemnt for  optimal use of mobile systems of mobile flood protection dams/barrires as  short-term flood prevention and non-permanent/ nonstructural measures in combination with the permanently existing protection works and infrastructures in the urban environment is the subject of this study.

As a field of application (case study) of this research and the evaluation of different flooding and intervention scenarios, a stream section of an important transboundary watercourse that flows through the city of Serres, Greece was chosen. For this stream, the river bed and the surrounding areas as well as the built environment and all the technical works along the stream were measured by land observation methods (topographic and remote sensing data).

In order to draw into conclusions, the assessment of the hydrological characteristics and the water flow characteristics of the stream and the catchment area was carried out. Then, the simulation of the hydraulic characteristics for the current state of the stream and for various different flooding scenarios through the use of mobile flood barriers/small dams of different types and geometrical characteristics was applied.

The result of the study has led to a “roadmap” of how, when and where non-permanent protection measures and can be implemented in urban environments, useful to local authorities and civil protection in charge.

The evaluation of the capacity and performance of mobile barrier systems (based on their characteristics) was carried out, in order to be  effectively used in varying flooding events, with different characteristics and in  site-specific locations in various scenarios, through hydraulic simulations. The results of the hydraulic simulations resulted in the barrier systems’ evaluation and the formation of a methodology, which concerns their application efficiency and their inter-operability in the pilot area, while determining the optimal management and the overall cost at the same time.

How to cite: Tzanou, E., Chatzigiannis, A., and Piliouras, M.: Pilot-scale application of mobile barrier systems for flood protection of urban areas. Assessment and evaluation of their interoperability in the urban area of Serres, Greece., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16291, https://doi.org/10.5194/egusphere-egu23-16291, 2023.

Flooding is among the most prevalent natural hazards worldwide, with increasing frequency and devastating impact. Urban floods are severe in Indian cities due to the culmination of changing climate, rapid urbanization, and intensive population growth. Transport infrastructure such as roads underpins economic activity enabling goods and human mobility. Evaluating the response against urban flooding is critical as disruption of the road system can result in cascading effects. The recent advancements in assessing the direct impact of urban flooding on road infrastructure are well explored. However, we lack a systematic approach to model and evaluate the direct, intangible, and indirect effects of extreme precipitation-induced urban flooding on road infrastructure systems in urban areas with unplanned drainage systems. Here in this study, we model the interaction between urban flooding and road transportation systems by integrating a hydrodynamic model with a network science approach for the coastal city of Kozhikode, India. We evaluated the response of the combined sewer drainage system against extreme precipitation events through the 1D-2D coupled flood model. While also identifying the resulting flood inundation characteristics- extent, propagation, and depth. Flood modeling results indicate the inundated roads and functionality loss of the road system for extreme precipitation events. Our initial assessment highlights that highly localized road network submergence due to flood inundation has a widespread and prolonged disruption in the system. The integrated framework and network functionality measures could help in future resilience assessment and in devising effective planning strategies for hazard mitigation in urban areas.

How to cite: Dave, R. and Bhatia, U.: Investigating the impact of extreme precipitation induced urban flooding on road network disruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-738, https://doi.org/10.5194/egusphere-egu23-738, 2023.

Urban flooding has gained great attention in recent years since population in urban areas have become more vulnerable to climatic extremes. The rate of urban flooding has increased around the globe mainly due to climate change. To cope with an increasing flooding issue, there has been an increased effort to manage flood management in urban areas. Similarly in this study, an attempt was made to develop a GIS based map to access flood resilience for the Gyor city. The Gyor city is particularly vulnerable to flooding due to its geographical proximity at the confluence of Raba, Rabca, Mosoni, Marcal and the great Danube rivers. Three elements i.e., hazard, Exposure, and coping capacity with each having pre-determined parameters were selected and processed through Analytic Hierarchy Process (AHP) technique. The product value map was then analyzed in ArcGIS using Specialized Flood Resilience Model (S-FRESI). The resultant product map shows that the majority of Gyorszentivan, Menfocsanak and Ipari Park districts have the very high resilience to floods, while most area of the  districts of Kismegyer, Nadorvaros,  Sziget, and Belvaros have very low resilience to floods. Similarly, the districts of Bacsa, Saras, Pinnyed, Gyimot and Likocs have most of the areas in medium resilience, while the remaining 6 districts possess areas with low, medium and high resilience. The study is very beneficial for future studies in assessing the areas that are more vulnerable to flooding and have low resilience and can help the decision makers to prepare a better urban flood management system.

How to cite: Ullah, I., Kovacs, G., and Lenner, T.: Urban Flood Resilience Assessment Using Arc GIS Based AHP Approach: A Case Study of Gyor City, Hungary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15092, https://doi.org/10.5194/egusphere-egu23-15092, 2023.

A report from World Bank in 2022 reveals that about 1.81 billion people (23% of the world population) are directly exposed to flood with depths greater than 0.15 meters. In this study, we evaluate the impact of extreme rainfall events on population in urban areas in Taiwan using SOBEK models. The validation results of the SOBEK models are promising with photos collected from social media for historical storm events. To further assess the impact of extreme rainfall events, we used design rainfall with hourly rainfall of 80mm/hr, 90mm/hr, and 100mm/hr derived from Simple Scaling Gaussian Markov (SSGM) method for single rainfall gauge within major urban area. These results are provided for disaster prevention authority to reinforce the flooding management in urban area.

How to cite: Wei, H.-P., Su, Y.-F., Chang, C.-H., and Yeh, K.-C.: Flood Simulation and Population Impact Analysis of Short-Duration Intense Rainfall in Urban Area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5027, https://doi.org/10.5194/egusphere-egu23-5027, 2023.

Due to climate change, the scale of flood damage by localized torrential rains in urban areas is on an increase. Meanwhile, the existing flood runoff analysis methods do not consider buildings in urban areas, resulting in an overestimation of the degree of flood damage. Therefore, this study presents a method to consider buildings when applying XP-SWMM for flood analysis in downtown areas where buildings are concentrated, in order to accurately simulate the flood spread pattern around the building. To propose an optimal method which considers buildings, water depth, maximum flooded area, and the flow pattern around the building were compared according to whether or not the building was applied. As a result of the study, the average flooded area was 172,900㎡ when the building was set as an inactive area, which was 64% of the average flooded area (271,000㎡) when the building was not considered. The average water depth was 0.32m when buildings were considered, which was 1.78 times deeper than the average water depth (0.15m) when buildings were considered. This is the reflection of the blocking effect of the building in the model analysis, resulting in a significant reduction of the flooded area. In addition, since the flood simulation considered the flow rate of the same volume, flow velocity and average submerged depth relatively increased. This study is expected to contribute to the establishment of optimal downtown flood measures, by presenting a method for accurate flood analysis using the XP-SWMM model considering the influence of buildings in urban areas. For further improvement in the accuracy of flood analysis, it would be necessary to develop flood simulation methods suitable for different basins with flood records.

This research was support by a (2022-MOIS63-002) of Cooperative Research Method and Safety Management Technology in National Disaster funded by Ministry of Interior and Safety(MOIS, Korea).

How to cite: Jun, K., Kim, S., Jung, M., and Lee, S.: 2D Flood Analysis considering Buildings in Urban Areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5522, https://doi.org/10.5194/egusphere-egu23-5522, 2023.