Preliminary Flood Risk Research Articles

Integrating hydro-geomorphological adjustments into flood mapping for enhanced risk assessment

Accurate flood risk assessment is essential for effective risk management, especially as extreme rainfall trends have increased flood frequency and inundation globally. However, rainfall data alone often becomes insufficient in dynamic floodplains, where geomorphological changes are critical. The Shilabati River basin in West Bengal, India, illustrates such a landscape, having experienced severe floods in 1959, 1967, 1968, 1973, 1978, 1999, 2000, 2007, 2013, and 2021. For this basin, mapping landform variability is key to understanding erosion and landscape denudation processes. The Digital Elevation Model (DEM)-based technique known as DEM of Difference (DoD) enables the detection of terrain changes over time by comparing DEMs from distinct periods, offering insight into floodplain erosion. However, DEM-based analysis is prone to spatially correlated errors, which can propagate false topographic features, hindering accurate flood mapping. Our study employs the Elevation Deviation Index (EDI), a DEM comparison method that normalizes and mitigates spatially correlated errors across terrain. Using EDI, we mapped geomorphological changes in the Shilabati floodplain, revealing substantial erosion and elevation loss. Our findings demonstrate a strong positive correlation between EDI values and increased flood extent. These results underscore the importance of incorporating geomorphological analysis in flood risk assessment, as hydrological data alone may overlook critical terrain changes. We recommend a Preliminary Flood Risk Assessment (PFRA) to strengthen flood resilience in the region, targeting vulnerable zones for enhanced, adaptive flood mitigation strategies.

Riverine flood potential assessment using metaheuristic hybrid machine learning algorithms

AbstractThis study presents the performance of stand‐alone and novel hybrid models combining the feed‐forward neural network (FFNN) and extreme gradient boosting (XGB) with the genetic algorithm (GA) optimization to determine the riverine flood potential at a local spatial scale, which is represented by the Gidra river basin, Slovakia. Eleven flood factors and a robust flood inventory database, consisting of 10,000 flood and non‐flood locations, were used. Using the FFNN, XGB, GA‐FFNN and GA‐XGB models, 16.5%, 11.0%, 17.1%, and 12.3% of the studied basin, respectively, is characterized with high to very high riverine flood potential. The applied models resulted in very high accuracy, that is, AUC = 0.93 in case of the FFNN stand‐alone model and AUC = 0.96 in case of the XGB stand‐alone model. The GA algorithm was able to raise the value of AUC for the hybrid GA‐FFNN and GA‐XGB models to 0.94 and 0.97, respectively. The results of this study can be useful, especially, for the identification of the areas with the highest potential for riverine floods within the next updating of the Preliminary Flood Risk Assessment, which is being carried out based on the EU Floods Directive.

Indicator-based approach for fluvial flood risk assessment at municipal level in Slovakia

The article focuses on the mapping and assessment of fluvial flood risk at municipal level of Slovakia. The fluvial floods risk index (FFRI), composed of a hazard component and a vulnerability component, was computed for 2927 municipalities using spatial multicriteria analysis and geographic information systems (GIS). The fluvial flood hazard index (FFHI) was computed based on eight physical-geographical indicators and land cover representing the riverine flood potential and also the frequency of flood events in individual municipalities. The fluvial flood vulnerability index (FFVI) was calculated using seven indicators representing the economic and social vulnerability of municipalities. All of the indicators were normalized and weighted using the rank sum method. By aggregating the weighted indicators, we obtained the FFHI and FFVI in each municipality. The final FFRI is a result of a synthesis of the FFHI and FFVI. The results of this study can be used mainly in the framework of flood risk management at national spatial scale, but also for local governments and periodic update of the Preliminary Flood Risk Assessment document, which is carried out at the national level under the EU Floods Directive.

Combined basin-scale and decentralized flood risk assessment: a methodological approach for preliminary flood risk assessment

In this study, we focused on a combined basin-scale and decentralized (localized) approach (municipalities) to riverine flood risk mapping and assessment in the Gidra River Basin (Slovakia). The methodology applies direct spatial and probabilistic relation among the physical processes of riverine flooding with a given vulnerability. Flood hazard mapping at basin scale was based on ungauged conditions. First, we calculated the design peak discharges using the rainfall generation model and rainfall-runoff model, in particular, the Stochastic Rainfall Generator (STORAGE) and the Continuous Simulation Model for Small and Ungauged Basins (COSMO4SUB). After that, we used the obtained flood scenarios for Hydrologic Engineering Center´s River Analysis System (HEC-RAS) hydraulic modelling. The modelled flood extent, flow depth, and velocity were considered as hazard indicators. The results were expressed in terms of flood hazard (FHI), vulnerability (FVI), and risk index (FRI): the highest values were obtained for municipalities located in the northern-central part of the investigated area. The proposed methodology can constitute a conceptual basis for updating the Preliminary Flood Risk Assessment (PFRA) in Slovakia.

Sustainable Stormwater Management at Urban Expansion Areas of Potential Significant Flood Risk

The Preliminary Flood Risk Assessment (PFRA) for the Greek territory, according to European Directive 2007/60/EC, was completed in 2012 and was revised in 2019. Areas of Potential Significant Flood Risk (APSFR) were defined (and revised) for each River Basin District (RBD). Meanwhile, in 2018, the Flood Risk Management Plans (FRMPs) were approved - by Greek Authorities - for each RBD. In the FRMPs specific measures are proposed for the funding of Stormwater Management (SM) projects that will be designed according to the principles of Sustainable Development (SD), i.e., Best Management Practices (BMPs), Green Infrastructure (GI), Low Impact Development (LID), Urban Natural Water Retention Measures (NWRM) and Sustainable Drainage Systems (SuDS). Within this framework, a preliminary study is drawn up in order to specify some innovative proposals for Sustainable Stormwater Management (SSM) in three areas located into the APSFR of RBD ‘EL11’ (Eastern Macedonia), located in Northern Greece. Two of these areas, Perigiali and Nea Peramos are coastal, while the third one, Doxato, is a continental, plain area. Urban expansion plans are approved for all three cases. The study proposes the implementation of an Innovative Stormwater Management Plan (ISMP) for each area.

Improving Estuarine Flood Risk Knowledge through Documentary Data Using Multiple Correspondence Analysis

Estuarine margins are usually heavily occupied areas that are commonly affected by compound flooding triggers originating from different sources (e.g., coastal, fluvial, and pluvial). Therefore, estuarine flood management remains a challenge due to the need to combine the distinct dimensions of flood triggers and damages. Past flood data are critical for improve our understanding of flood risks in these areas, while providing the basis for a preliminary flood risk assessment, as required by European Floods Directive. This paper presents a spin-off database of estuarine flood events built upon previously existing databases and a framework for working with qualitative past flood information using multiple correspondence analysis. The methodology is presented, with steps ranging from a spin-off database building process to information extraction techniques, and the statistical method used was further explored through the study of information acquired from the categories and their relation to the dimensions. This work enabled the extraction of the most relevant estuarine flood risk indicators and demonstrates the transversal importance of triggers, since they are of utmost importance for the characterization of estuarine flood risks. The results showed a relation between sets of triggers and damages that are related to estuarine margin land use, demonstrating their ability to inform flood risk management options. This work provides a consistent and coherent approach to use qualitative information on past floods, as a useful contribution in the context of scarce data, where measured and documentary data are not simultaneously available.

Riverine flood potential assessment at municipal level in Slovakia

Study regionSlovakia – 2927 municipalities. Study focusThis study maps and assesses the riverine flood potential in municipalities of Slovakia using the vector-based spatial multi-criteria analysis and geographic information systems (GIS). The flood potential index (FPI) in municipalities was computed based on eight flood factors, which were normalized, weighted and aggregated into the FPI index. Furthermore, we analyzed the spatial clusters of riverine flood potential using the local Moran’s coefficient of spatial autocorrelation. New hydrological insights for the regionThe very high and high FPI (767 municipalities) was recorded mostly in municipalities of northern and eastern Slovakia. Very low and low FPI (1452 municipalities) dominates in western and southern Slovakia while moderate FPI (708 municipalities) was mainly recorded in municipalities of central Slovakia. The number of statistically significant high-high and low-low spatial clusters of riverine flood potential was 16 (524 municipalities) and 18 (487 municipalities), respectively. Clusters of positive spatial autocorrelation are mostly located in the northern and eastern Slovakia, one cluster in western Slovakia and seven clusters in central Slovakia. Clusters of negative spatial autocorrelation are mostly located in western and southern Slovakia and three clusters in eastern Slovakia. The proposed methodology can be useful for regular updating of Preliminary Flood Risk Assessment (PFRA) in Slovakia under the EU Floods Directive.

Morphometric-hydro Characterization of the Coastal Line between El-Qussier and Marsa-Alam, Egypt: Preliminary Flood Risk Signatures

Egypt is highly exposed to flash flood hazards, particularly in Sinai Peninsula and along the Red Sea coast, causing sudden and huge damages to constructions and huge losses in human lives during a very short time. This paper investigates the dominant characterization of morphometrical features and their relationships with the hydrological behaviors along an important strip of the western Red Sea coast. The study focuses on analyzing the October 2009 and 2019 storm events along the coastal area between EL-Qussier and Marsa Alam in order to intiate a preliminary flood risk assessment model. Morphometric features along the entire study zone provide a complete scenario of the nature of the catchments and sub-catchments development. Numerous morphometric indexes such as catchments geometry, areal indexes, linear indexes, and relief indexes were examined through processing different sets of data. Modern techniques such as remote sensing and geospatial analysis were applied to process different spatial and spectral data. The hydrological model (HEC-HMS) in the WMS software was run to delineate the catchments and sub-catchments and extract the peak flow hydrograph curves for the main catchments. The results of the water amounts and peak flow were calculated using the SCS unit hydrograph approach. The hydrological characteristics of the major catchments reveal conditions for moderate levels of flash flooding. The study ended with a number of recommendations that could minimize the negative effects of the flash flood hazards.

FLOOD AS ONE OF THE MANIFESTATIONS OF HARMFUL EFFECTS OF WATER ON THE EXAMPLE OF FOUR UNITED TERRITORIAL COMMUNITIES OF ODESSA REGION

Flooding is one of the manifestations of the harmful effects of water, which is strongly manifested around the world. Its manifestations are recorded in Ukraine, mainly in the western regions. In the central, eastern and southern regions, periodic flooding is observed in the basins of large rivers (Danube, Dniester, Dnieper, etc.). With the beginning of the XXI century local periodic flooding is increasingly recorded in other areas. And if in the western regions we know almost everything about the causes and risks of flooding, in other areas there is almost no research and knowledge. Recognizing the significant economic and social damage from flooding at the state level, the Ministry of the Interior issued an order approving the "Preliminary Flood Risk Assessment Methodology" designed to carry out a preliminary flood risk assessment to identify areas with potentially significant flood risks in all areas river basins of Ukraine, and other possible sources of flooding, to minimize the negative consequences associated with flooding, which have an impact on human health, environment, economy, cultural heritage, etc. To do this, it was necessary to create a risk passport within each settlement (SM), but in most of them they are missing. The aim of the work is to show an effective approach to solve the problem of preventing such a negative phenomenon as flooding in the southern regions on the example of four associations of territorial communities (TC) of Belgorod-Dniester district (formerly Tatarbunary). The subject of the study were the factors of formation of this negative phenomenon within 34 SM. To solve this problem, an approach (algorithm), which consists of three main stages and the application of GIS programs Arc Map method 3D analysis, is proposed. At the same time, one of the main elements of the study was the existing hydraulic structures (HS). Based on the results of work within each state of emergency, the types, location, quantity and technical condition of the HS were determined. Maps of availability and technical condition of the HS, places of possible flooding with the direction of the main water flows are compiled in electronic form. The approach mentioned in this paper allows to minimize, and in some places to remove in the future such a negative phenomenon as flooding within a single state of emergency.

GIS-Based Spatial and Multi-Criteria Assessment of Riverine Flood Potential: A Case Study of the Nitra River Basin, Slovakia

The aim of this study was to identify the areas with different levels of riverine flood potential (RFP) in the Nitra river basin, Slovakia, using multi-criteria evaluation (MCE)-analytical hierarchical process (AHP), geographic information systems (GIS), and seven flood conditioning factors. The RFP in the Nitra river basin had not yet been assessed through MCE-AHP. Therefore, the methodology used can be useful, especially in terms of the preliminary flood risk assessment required by the EU Floods Directive. The results showed that classification techniques of natural breaks (Jenks), equal interval, quantile, and geometric interval classified 32.03%, 29.90%, 41.84%, and 53.52% of the basin, respectively, into high and very high RFP while 87.38%, 87.38%, 96.21%, and 98.73% of flood validation events, respectively, corresponded to high and very high RFP. A single-parameter sensitivity analysis of factor weights was performed in order to derive the effective weights, which were used to calculate the revised riverine flood potential (RRFP). In general, the differences between the RFP and RRFP can be interpreted as an underestimation of the share of high and very high RFP as well as the share of flood events in these classes within the RFP assessment. Therefore, the RRFP is recommended for the assessment of riverine flood potential in the Nitra river basin.

Comparison of multi-criteria-analytical hierarchy process and machine learning-boosted tree models for regional flood susceptibility mapping: a case study from Slovakia

Identification of areas susceptible to floods is an important issue which requires an increased attention due to the changing frequency and magnitude of floods, which is mainly a result of the ongoing climate change and increasing anthropic pressure on the landscape. In this study, the aim was to identify the areas susceptible to floods using and comparing two different approaches, namely the multi-criteria decision analysis-analytical hierarchy process (MCDA-AHP) and the machine learning-boosted classification (BCT) and boosted regression (BRT) tree. The study area was represented by the Topľa river basin, Slovakia. Altogether, seven relevant flood conditioning factors: elevation, slope, river network density, distance from river, flow accumulation, curve numbers and lithology as well as flood inventory database consisting of 107 flood locations were used. Based on the results, almost 40% of the study area is characterized by high to very high flood susceptibility using the MCDA-AHP. In case of the BCT and BRT models, the share of high and very high flood susceptibility class on the basin area is 45% and 38%, respectively. Validation of the performed flood susceptibility models confirmed generally higher accuracy of the machine learning models. The accuracy of the MCDA-AHP model was 81.33% while the accuracy of the boosted tree models was 87.70% and 91.42%, respectively, for classification and regression. The results of this study can enhance more effective preliminary flood risk assessment according to the EU Floods Directive.

Spatial and temporal aspects of high streamflow periods within the Danube drainage basin in Bulgaria

High flow events are the main prerequisites for floods with negative social and environmental consequences. Their study under uncertain and changing climate gives informative knowledge for further management decisions. This paper seeks to analyze the spatio-temporal parameters of high flow periods within the Danube drainage basin in Bulgaria. Three characteristics of the hazard phenomena: time of occurring, frequency and duration are investigated. The analysis is based on daily discharge data collected from 20 gauging stations for the period 2000–2005. The surplus water quantities are identified by the Threshold level method using fixed values – Q25 and Q5, derived from the flow duration curve. Results show a concentration of the high flow periods during the spring hydrological season, with an average duration up to six weeks. The calculations establish positive correlations between the duration of high flow, the altitude of catchments, and the density of drainage network. The resulting information can serve as a support for the development of preliminary flood risk assessments in the Danube River Basin.

GIS-based comparative assessment of flood susceptibility mapping using hybrid multi-criteria decision-making approach, naïve Bayes tree, bivariate statistics and logistic regression: A case of Topľa basin, Slovakia

Abstract Flood is a devastating natural hazard that may cause damage to the environment infrastructure, and society. Hence, identifying the susceptible areas to flood is an important task for every country to prevent such dangerous consequences. The present study developed a framework for identifying flood-prone areas of the Topľa river basin, Slovakia using geographic information system (GIS), multi-criteria decision making approach (MCDMA), bivariate statistics (Frequency Ratio (FR), Statistical Index (SI)) and machine learning (Naive Bayes Tree (NBT), Logistic Regression (LR)). To reach such a goal, different physical-geographical factors (criteria) were integrated and mapped. To access the relationship and interdependences among the criteria, decision-making trial and evaluation laboratory (DEMATEL) and analytic network process (ANP) were used. Based on the experts’ decisions, the DEMATEL-ANP model was used to compute the relative weights of different criteria and a GIS-based linear combination was performed to derive the susceptibility index. Separately, the flood susceptibility index computation through NBT-FR and NBT-SI hybrid models assumed, in the first stage, the estimation of the weight of each class/category of conditioning factor through SI and FR and the integration of these values in NBT algorithm. The application of LR stand-alone required the calculation of the weights of conditioning factors by analysing their spatial relation with the location of the historical flood events. The study revealed that very high and high flood susceptibility classes covered between 20% and 47% of the study area, respectively. The validation of results, using the past flood points, highlighted that the hybrid DEMATEL-ANP model was the most performant with an Area Under ROC curve higher than 0.97, an accuracy of 0.922 and a value of HSS of 0.844. The presented methodological approach used for the identification of flood susceptible areas can serve as an alternative for the updating of preliminary flood risk assessment based on the EU Floods Directive.

Analysis of Climate Change’s Effect on Flood Risk. Case Study of Reinosa in the Ebro River Basin

Floods are one of the natural hazards that could be most affected by climate change, causing great economic damage and casualties in the world. On December 2019 in Reinosa (Cantabria, Spain), took place one of the worst floods in memory. Implementation of DIRECTIVE 2007/60/EC for the assessment and management of flood risks in Spain enabled the detection of this river basin with a potential significant flood risk via a preliminary flood risk assessment, and flood hazard and flood risk maps were developed. The main objective of this paper is to present a methodology to estimate climate change’s effects on flood hazard and flood risk, with Reinosa as the case study. This river basin is affected by the snow phenomenon, even more sensitive to climate change. Using different climate models, regarding a scenario of comparatively high greenhouse gas emissions (RCP8.5), with daily temperature and precipitation data from years 2007–2070, and comparing results in relative terms, flow rate and flood risk variation due to climate change are estimated. In the specific case of Reinosa, the MRI-CGCM3 model shows that climate change will cause a significant increase of potential affected inhabitants and economic damage due to flood risk. This evaluation enables us to define mitigation actions in terms of cost–benefit analysis and prioritize the ones that should be included in flood risk management plans.

Preliminary flood risk assessment: Case study of systematic processing of available or readily derivable information

AbstractThe paper presents a methodological approach to preliminary flood risk assessment, which is conceptually based on the regional typing and integrated flood risk assessment. From the above conceptual bases, two key tasks arise: (1) establishing a basic spatial unit for preliminary flood risk assessment and (2) specifying its attributes in relation to the flood hazard and vulnerability (negative consequences), which correspond to assessment on a national scale. The basic spatial unit is defined as the municipality district. The methodological procedure of the preliminary flood risk assessment is based on an assessment of the impact of the district’s attributes on the potential of the flood hazard and negative flood consequences in the form of indicators, which are aggregated to subindices and indices. The flood risk potential index is determined as an aggregation of the flood hazard potential index and flood consequences potential index.

Flood maps and their potential role in local spatial planning: a case study from Slovakia

Abstract The article is focused on the creation of flood maps for ungauged basins (i.e. local spatial scale areas), using a hydrologic-hydraulic approach, geographic information systems (GIS) and remote sensing techniques, and their role in local spatial planning. The case study is represented by the Turniansky potok catchment which was not mapped in the preliminary flood risk assessment (EU Floods Directive) as an area with existing potential risk. The design discharges were estimated by applying the regional formula. The design discharge with 100-year return period was chosen for hydraulic modeling using the one-dimensional HEC-RAS model. The basis for creating the flood vulnerability map for the selected hydraulic domain was the current land use. Each land use category was assigned a category of acceptable risk (low, medium, high). Furthermore, the vulnerability was defined by digitizing buildings within the hydraulic domain. The role of the created flood maps, as regulatory tools in local spatial planning (i.e. local development plan of municipality), was highlighted and discussed. The importance of flood maps is primarily seen in limiting the irresponsible expansion and densification of construction in the areas near the watercourse which were assigned the low acceptable risk.

Hydrological and flood hazard assessment using a coupled modelling approach for a mountainous catchment in Portugal

Floods may lead to destruction of property, to damage to the environment and ultimately to loss of lives. Although it is not possible to avoid them, they are enhanced by human activities that increase the probability of occurrence of these natural events. Preliminary flood risk assessment and determination of areas of potential significant flood risk is mandatory according to the European Floods Directive (2007). In order to meet the established legislation, a methodology was developed that couples two modelling approaches: the Hydrological Simulation Program—FORTRAN (HSPF) and IBER. A target watershed, with complex orography and known to be vulnerable to flood hazards, is selected: the Vez River (northern Portugal). The performance of the HSPF model, driven by a climate gridded dataset, was assessed, followed by the reconstruction of the flow rate in the catchment for the period from 1950 to 2015. The results hint at an agreement between simulated and observed daily flow rates, with high coefficient of determination value and of the Nash–Sutcliffe coefficient of efficiency (> 0.7 daily timescale). A satisfactory performance was also found in reproducing flood peak events. An average deviation of 10% was found between observed and simulated flood peaks. The output of HSPF was subsequently used to drive IBER, thus determining flood hazard areas for a 10, 50 and 100-year return periods. The methodology presented here provides basic tools for decision-makers to evaluate hydrologic responses to climate data, namely the determination of flood hazard maps, but also risk assessment, water management, environmental protection and sustainability.

Flood risk management in Europe: the EU ‘Floods’ directive and a case study of Ireland

ABSTRACTThe ‘Floods’ Directive sets out a basic framework for good practice in flood risk management comprising a screening exercise, the Preliminary Flood Risk Assessment, to identify the Areas of Potentially Significant Flood Risk (APSFRs), and then the preparation of flood maps for these areas, and the preparation of flood risk management plans to set out measures to address the flood risk in the APSFRs. The Directive provides significant subsidiarity to allow the Member States to determine how best to apply the framework in the most appropriate way given the legacy and context of flood risk management within their own country. As a result, the Member States have taken a range of diverse approaches in applying the requirements of the Directive. In Ireland, a major national programme of analysis has delivered on the requirements of the Directive that has involved the development of a range of new approaches and methodologies. These have included bespoke methods of broad-scale risk assessment, and the development of weighted objectives reflecting societal values for use in a Multi-Criteria Analysis to determine the most appropriate flood risk management measures for each community at risk. This paper reflects on some of the issues and challenges faced in implementing the ‘Floods’ Directive across the EU, and outlines as a case study how the Directive has been implemented in Ireland.

Identification of Significant Flood Areas in Lithuania

During preliminary flood risk assessment in Lithuania 54 significant flood areas (SFA) were identified. The detailed flood hazard and risk maps were prepared for these areas in 2014. European Union Floods Directive does not indicate the concrete criteria for SFA delineation. The uncertainty analysis shows that the total length of SFA is not very sensitive to used methodology. In some rivers the uncertainties of 100 year flood peek discharge (Q1%) were large, but the variation of SFA boundary location was relatively small due to properties of hydrological network. The catchment area and Q1% change rapidly near the junction with large tributaries, so the boundaries of SFA are usually attached to these junctions. The formal criteria are mostly used to evaluate the possibility of significant floods, but the delineation of SFA is usually based on subjective decision.

The Assessment of Level of Flash Floods Threat of Urbanised Areas

Flash floods (or torrential rain flooding) is another type of flood hazard which has caused casualties and significant property damages. A methodology for identification of urban areas, which can potentially be burdened by that type of flood hazard, was proposed. This method, also called Method of Critical Points (CP), is a repeatable process able to identify areas, which are significant in terms of formation of surface run‑off and erosion. As addition to the preliminary flood risk assessment according to EU Directive 2007/60/ES on the Assessment and Management of Flood Risks, the presented methodology was applied for the entire area of the Czech Republic and the results are being used for the updating of non‑technical measures, e.g. urban planning. In the article, the principles of methodology of CP are described and results of the first application in the Czech Republic are presented, as well as possible interpretations of them.