As cities have expanded into floodplains, the need for their protection has become crucial, prompting the evolution of flood studies. Here, we describe the operational tools, methods and processes used in flood risk engineering studies in the 1970s, and we evaluate the technological progress up to the present day. To this aim, we reference relevant regulations and legislation and the recorded experiences of engineers who performed hydrological, surveying and hydraulic studies in the 1970s. These are compared with the operational framework of a contemporary flood risk assessment study conducted in the Pikrodafni basin in the Attica region. We conclude that, without the technologically advanced tools available today, achieving the level of detail and accuracy in flood mapping that is now possible would have been unfeasible, even with significant human resources. However, ongoing urban development and growth continue to encroach upon flood plains that have existed for centuries, contributing to increased flood risk.

The assessment of human progress often relies on factors such as the availability of energy and resources, the improvement of life expectancy, education, equality, democracy, justice, civilization, and other crucial elements. A significant concern within this evaluation revolves around the inclusivity and accessibility of technological advancements. However, human progress is more than that, since it can also manifest itself in the scientific and technical advances in treating natural hazards presenting a diachronic issue to societies’ resilience. In this study, the progress of engineering in analyzing and managing flood risk between the 1970s and present times is evaluated. To this aim, we utilize the experience of engineers who completed surveying, hydrological, and hydraulic studies for flood risk assessment in the 1970s, to carry out comparisons with recent methodologies applied in the framework of the Programming Agreement between the Prefecture of Attica and 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) to the Pikrodafni stream, in Attica, Greece. Specifically, we quantify the progress made and differences between the two periods, in terms of human resources, computational cost, and accuracy of practices and methodologies.

Ιn the framework of the Programming Agreement between the Prefecture of Attica and 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), a rather innovative approach is applied for the purpose of flood risk assessment, regarding the contribution of citizens to the identification of the areas which are vulnerable to flood. It is highlighted how the experience of residents can lead to the identification of areas prone to flood, which could not be easily located otherwise, especially through large-scale flood risk maps. Moreover, it is demonstrated how the knowledge of residents can be used as a validation tool for the flood risk assessment results. Consequently, it is argued that the residents must play an active role in the conception, design and implementation of flood protection works in any infrastructure project within their area of interest. Such implementations of any mitigation measures should have as a prerequisite their acceptance by the residents. Their understanding is also important, on the one hand, to deal with possible reactions, appeals, and conflicts throughout the execution of the project, and, on the other hand, to ensure that residents are properly informed about the utility of such works and projects.

Urban areas characterized by high density of population and infrastructure can be extremely prone to floods. The flood modeling and management of these areas present high complexity due to their distinctive features. Therefore, advanced methodologies for an accurate assessment of urban flood processes need to be developed. This study presents the methodology and the results for flood risk assessment at high spatial resolution of the Kifissos river basin in Greece. This is the largest one of the five flood-stricken river basins in the region of Attica that are studied in the framework of the Programming Agreement between the Prefecture of Attica and 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). Kifissos basin is highly urbanized (80% of the river basin), has been affected by forest fires over the last years, and contains a complex hydraulic network (60% of the total river network is artificial). Thus, the modelling of a river basin with many hydraulic works is a significant challenge, which needs to be addressed to simulate the current situation of the river flow and support the expanding constructions. HEC-RAS 6.4.1 hydraulic model is used for the flood hazard assessment for 50, 100 and 1000 years return period using earth observation, as well as spatial and field data. The vulnerability is estimated by combining different disaster resilience parameters, such as population density, population age and building type, applying different weights. Flood risk is assessed on the impact of hazard, total vulnerability, and economic exposure. Alongside the model’s results including the inundated areas, the flow depths and consequently the flood risk, critical points identified from the field visits are also presented and classified in risk priority. Thus, the presented results are cross-checked with the high-risk areas pointed out from the authorities as well as the civilians’ calls to the Fire Brigade for water pumping over the last 15 years.

Floods affect many regions of the world every year and are the most deadly natural hazard. The increasing pressures of a growing global population, widespread ecosystem degradation, and the compounding effects of climate variability and change are significantly increasing flood risks worldwide. Hydrodynamic models, combined with Earth Observations (EO), play an increasingly important role in the comprehensive analysis and characterization of floods, providing a deeper understanding of their dynamics in past, present, and future scenarios.Under the “Copernicus Emergency Management Service (CEMS) Risk and Recovery Mapping (RRM)” framework, this on-call study (i.e., CEMS activation “ΕMSN: Retrospective flood temporal analysis of floods in Saarland, Germany”) focused on the mid-May 2024 (16/05/2024-22/05/2024) flood in Saarland, Germany, which resulted in extensive damage across the Saarland state capital Saarbrücken and several districts in Saarland. Leveraging advancements in Earth observation (EO), this study integrated multi-source remote sensing data into a 2D hydraulic modeling framework to enhance the understanding of flood dynamics in the region through a comprehensive temporal analysis.Using the HEC-RAS hydraulic modeling open-source software of the United States Army Corps of Engineers (USACE), a rain-on-grid approach was employed to simulate direct rainfall runoff to supplement fluvial model simulation of flood propagation over a 7-day period. Model calibration was based on observed water depth data from Gauging stations’ recordings, with adjustments made to improve accuracy. Validation was conducted using EO-derived flood delineations from multitemporal post-event imagery, spanning multi-Platform Satellite products including SAR (Sentinel-1A, RadarSat-2, COSMO-SkyMed and TerraSAR-X) and Optical (Planet Scope) imagery. Therefore, the outputs of the study including the water depth and the flood persistence were derived from the combination of the hydraulic modeling and remote sensing methodologies.Despite the relatively lower flood thematic accuracy of EO-derived flood outlines in urban and forested areas given the inherent limitations of the SAR analysis techniques, the availability of multitemporal EO imagery was decisive in validating the hydraulic modelling accuracy and robustness. The study findings emphasize the emerging potential of EO data for validating hydraulic models and therefore enhancing flood mapping and monitoring capabilities. In this context, the availability of multitemporal EO datasets further enhanced the flood modelling performance in providing a better insight into the flood propagation and dynamics over the whole period of impact.Acknowledgment: The service took place under the Framework Service Contract 945236–IPR–2023 “Copernicus Emergency Management Service (CEMS) Risk and Recovery Mapping (RRM) Tailor-Made Products. We would like to acknowledge the great support of the JRC CEMS team memebrs, namely Guido Di Carlo, Cristina Rosales Sanchez, and Emanuele Sapino, for the completion of this service contract.

From the perspective of a team of engineers that studies an area in order to estimate flood risk, a highly studied area presents both benefits and challenges. On the one hand, stands the benefit of accessibility to data and existing knowledge, while on the other the challenge of optimal analysis and utilization of such material.The region of Attica, Greece, fits exactly the description of a highly studied area. It hosts the capital of the country, Athens, and close to half of the national population. For this reason, flood risk has been studied throughout the 20th and 21st century in various spatial scales, and using different methods and tools. In a contemporary study of flood risk with modern digital computational tools, we undertook the tasks of compiling, analyzing and mapping important information from those past studies.In this work, we present the relevant challenges faced during the project “Earthquake, fire and flood risk assessment in the Region of Attica” as well as inferences for future studies of similar type. Following the previous step of our comprehensive methodology for the estimation and mapping of flood risk in Attica Region, we received as an input a set of existing studies for our study area. In the process of abstracting the spatial data from those studies, we grouped such data in three categories: spatial information in text, in CAD files and in GIS files. Each type of information presented its own type of challenges. Information in text was time-consuming to process, both because it necessitated reading the whole studies to be pinpointed, but also due to the requirement for manual extraction and conversion to GIS format. Spatial information found in CAD and GIS files presented mostly software-related challenges in managing to achieve a common representation scale and geospatial reference of the plans. Lastly, a challenge that was common for all types of data was the identification of whether the hydraulic works or terrain conditions that were presented in each study were actually present as such today. This required cross-methodological communication including both with the previous methodological steps of contact with the institutions that provided the studies, and with the next methodological steps of site visits for the confirmation of the recorded information.Overall, we identify the following as crucial priorities for efficient abstracting and synthesizing the spatial data on flood risk in a highly studied area. Firstly, clarity in defining the types of data being searched for, secondly, the utilization of CAD and GIS software with interoperability functions and easy scaling and georeference functionalities, thirdly, the direct communication with the institutions that created or utilize the studies, and lastly, the realization of site visits to verify the recorded information.