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Flood events are the most commonly occurring natural disaster, with over 5 million properties at risk in the UK alone. Changes in the global climate are expected to increase the frequency and magnitude of flood events. Flood hazard assessments, using climate projections as input, guide policy decisions and engineering projects to reduce the impact of large return period events. Probabilistic flood modeling is required to take into account uncertainties in climate model projections. However, the dichotomous relationship between probabilistic modeling, computational cost and model resolution limits the applicability of such techniques. This paper examines improvements to traditional Monte Carlo methods using Latin hypercube sampling (LHS) and Multi‐level Monte Carlo (MLMC) to quantify the uncertainty in flood extent resulting from input hydrograph uncertainty. The results demonstrate that MLMC is a more efficient modeling strategy than current methods (i.e., traditional Monte Carlo) with high resolution outputs produced in less time than previously possible. The novel application of MLMC technique to three Scottish case studies, demonstrating a variety of river characteristics, domain sizes and computational costs, using a high resolution 5 m grid resulted in a 99.2% reduction in computational cost compared to traditional Monte Carlo methods and up to 2.3 times speedup over Latin Hypercube Sampling. Key Points: Multi‐level Monte Carlo (MLMC) reduces the computational cost by 99.2% over traditional full Monte Carlo; tested across a range of case studiesProbabilistic flood hazard assessment accuracy can be increased by incorporating higher resolution models with minimal increase in costsMLMC allows realistic uncertainty quantification at previously unfeasible 5 m grid resolution, yielding converged estimates of flooded area [ABSTRACT FROM AUTHOR]

A wide range of nature‐based solutions for flood hazard management work by storing and slowing flow within catchments, and therefore, there is a need to identify the optimal locations for implementing these solutions. This paper presents a relative scoring‐based mapping of the likely locations that contribute to the flood peak. Targeting flow reduction and attenuating mitigation actions in these locations can be an effective way to reduce flood damages at impact points downstream. The presented tool, SCIMAP‐Flood, uses information on land cover, hydrological connectivity, flood generating rainfall patterns and hydrological travel time distributions to impacted communities to find the potential source areas of flood waters. The importance of each location in the catchment is weighted based on its contribution to the flood hazard at each of the downstream impact points. In the example application, SCIMAP‐Flood is applied at a 5‐m grid resolution for the River Eden catchment, Cumbria, England, to provide sub‐field scale information at the landscape extent. Therefore, the tool can identify sub‐catchments where more detailed work can test different mitigation measures. [ABSTRACT FROM AUTHOR]

Among several devastating natural hazards, flooding is a common and serious threat to society causing huge loss of lives, properties, and infrastructure throughout the world. The intensity and frequency of this extreme weather event are expected to increase due to significant changes in the present‐day climate and land use and land cover (LULC) pattern. India has a very systematic and organized structural program and policies but lacks proper implementations, and adverse effect of climate change and the extreme event goes on in society. This paper is an analysis of floods in India and hazards due to climate change and LULC change patterns. Three models, namely "Eco‐biogeography‐based optimization (EBO), Random forest (RF), and Support vector machine (SVM)" were used to obtain the final output to prepare a "Flood susceptibility map". The result was validated through the "Receiver operating characteristics (ROC)" with "Area under curve (AUC)" values. The future rainfall scenario has been estimated by considering the "General circulation models" through different "shared socioeconomic pathways (SSPs)". The values of AUC are 0.915 (EBO), 0.887 (RF), and 0.869 (SVM), respectively. After consideration of different SSPs, the result shows that there is an increasing tendency of flood hazards in the projected period. Among all the employed modelling approaches, the EBO model has notable potential in delineating the possible flood‐prone regions for effective flood planning and management. Decision‐makers can benefit from country‐specific information and regional planner to implement sustainable and long‐term measures to overcome this type of hazardous situation. [ABSTRACT FROM AUTHOR]

Probabilistic methods are widely adopted for residual flood hazard assessment in flood‐prone areas protected by levees. Such methods can consider various sources of uncertainty, including breach location and flood event characteristics, and allow for the quantification of the result confidence. However, the possible occurrence of multiple levee breaches during the same flood event is usually disregarded. This paper presents a probabilistic method based on levee fragility functions and basic probability rules to estimate the probability of selected breach scenarios, including multiple breaching events. The flood hazard classification is based on inundation variables calculated for flood events of different return periods. A combined 1D‐2D hydrodynamic model is used for flood simulations. Probabilistic inundation extent maps and probabilistic flood hazard level maps are then created. Finally, probabilistic flood hazard estimates are summarized in a map of a suitable central tendency of the hazard level, coupled with a map of the Shannon entropy as an uncertainty indicator. This pair of statistical maps provides concise and effective information on a reference flood hazard along with the associated uncertainty. The method was applied to a region located along the middle reach of the Po River (northern Italy). Comparable central flood hazard estimates are obtained for the two sets of breaching events including or not including multiple breaches, with higher uncertainty if multiple breaches are considered. This result highlights the importance of considering multiple breaching events in flood risk management. Key Points: A probabilistic method is presented for flood hazard mapping in flood‐prone areas protected by levees, considering multiple breachesBreach scenario probabilities for selected return periods are estimated using levee fragility functions and basic probability rulesA "central" hazard level map and an entropy index map are introduced to summarize probabilistic information on flood hazard [ABSTRACT FROM AUTHOR]

Copyright of World Water Policy is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Critical national infrastructures, including energy, transport, digital communications, and water, are prone to flood damage. Their geographical extent is a determinant of, and is determined by, patterns of human development, which is often concentrated in floodplains. It is important to understand how infrastructure systems react to large‐scale flooding. In this paper, we present an integrated framework for critical infrastructure flood impact assessment. Within this integrated framework, we represent interdependent infrastructure assets through spatial network models. We quantify infrastructure flood impacts in terms of disrupted customers linked directly to flood assets and customers disrupted indirectly due to network effects. The analysis shows how spatial network models inform flood risk management practitioners to identify and compare critical infrastructures risks on flooded and non‐flooded land, for prioritising flood protection investments and improve resilience of cities. A case study of the Thames catchment in England is presented, which contains key infrastructure assets and highest population concentrations in United Kingdom. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to obtain more detailed information about flood insurance in municipalities of Slovakia situated in headwater basins. Analysis of insurance data from the period 2002–2011 showed a dramatic decrease in flood insurance. We found that the declining social status of the municipality's inhabitants is accompanied by a decrease in flood insurance policies. Further analysis revealed an increase in the number of flood insurance policies, flood insurance events and claims, with an increasing frequency of the occurrence of third‐level flood emergencies in municipalities. However, this influence was not substantiated when it came to the flood hazard potential of given municipalities. On the other hand, a comparatively high number of flood insurance events when no third‐level flood emergencies have been announced indicates that a relatively significant part of flood insurance events is caused by other types of flooding other than river flooding. [ABSTRACT FROM AUTHOR]

This work focuses on the analysis of flood fatalities in Greece, between 1970 and 2010. To this end, the paper develops and studies a systematic record of 151 flood-related fatalities that occurred across the country during this period. Based on this inventory and detailed incident reports, a database is developed, to examine the temporal, spatial and seasonal distribution of these incidents and the circumstances under which they occur. Analysis indicates that fatalities present a strong seasonality but show no particular temporal trends. Fatal incidents occur mostly during nighttime, outdoors and in rural areas of the country. Vehicle-related deaths are the most common type of incident, regarding the activity of victims, whereas other outdoor and indoor types of incidents present smaller percentages. Drowning was found to be the most common etiology of death. Males and elderly individuals showed proportionally higher representation, indicating an increased risk of these population groups to flooding. [ABSTRACT FROM AUTHOR]

The frequency of floods has been projected to increase across Europe in the coming decades due to extreme weather events. However, our understanding of how flood frequency is affected by geomorphic changes in river channel capacity remains limited. This paper seeks to quantify the influence of trends in channel capacity on flood hazards. Measuring and predicting the effect of geomorphic changes on freshwater flooding is essential to mitigate the potential effects of major floods through informed planning and response. Hydrometric records from 41 stream gauging stations were used to measure trends in the flood stage (i.e. water surface elevation) frequency above the 1% annual exceedance threshold. The hydrologic and geomorphic components of flood hazard were quantified separately to determine their contribution to the total trend in flood stage frequency. Trends in cross-sectional flow area and mean flow velocity were also investigated at the same flood stage threshold. Results showed that a 10% decrease (or increase) in the channel capacity would result in an increase (or decrease) in the flood frequency of approximately 1.5 days per year on average across these 41 sites. Widespread increases in the flood hazard frequency were amplified through both hydrologic and geomorphic effects. These findings suggest that overlooking the potential influence of changing channel capacity on flooding may be hazardous. Better understanding and quantifying the influence of geomorphic trends on flood hazard will provide key insight for managers and engineers into the driving mechanisms of fluvial flooding over relatively short timescales. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Flood management activities require development of flood maps that depict the spatial and temporal extent of floods with the help of hydrodynamic models. Two‐dimensional (2‐D) hydrodynamic models are frequently employed for flood inundation modeling and mapping with the help of high‐end computational resources and high‐resolution terrain information such as LiDAR (light detection and ranging) data. However, LiDAR data are either unavailable or not freely accessible in many parts of the world, especially in nations belonging to Global South. Hence, one‐dimensional (1‐D) models are still in practice owing to their lesser computational cost and data requirement. Nonetheless, the successful application of a 1‐D model depends mainly on the representation of the natural river and floodplain geometry, which is the primary input in the form of discrete cross‐sections. The assumed flow directions on floodplains while orienting the cross‐sections in 1‐D models induce some uncertainty in the model simulations. This study aims to evaluate the variability in the model simulations caused by the cross‐sectional orientations. Flood simulations were performed using a 1‐D hydrodynamic model for six different cross‐sectional realizations for three river reaches, having distinct morphological and topographical characteristics, and were compared with the simulations of a 2‐D hydrodynamic model and available reference inundation maps. The study suggests that the simulations of flood inundation extent and maximum flow depth variation are influenced by the cross‐sectional orientation on flood plains in river reaches characterized by broad flood plains with complex local topographical variations. In contrast, for reaches with relatively less wide and complex terrains, 1‐D models can generate robust simulations of flood inundation extent and spatial variation in maximum flood depth (R2 and NSE greater than 0.89) for high flood events. [ABSTRACT FROM AUTHOR]

Continuing land subsidence can aggravate flood hazard and diminish the effectiveness of existing flood mitigation systems. This paper presents a study of groundwater‐ pumping management for mitigating flood hazard in a subsidence infested area in the southwest coast of Taiwan. An optimal groundwater‐pumping model is developed for preventing flood hazard from worsening and for satisfying the groundwater demand. In an area where the land is susceptible to pumping‐induced subsidence, the study shows that proper long‐term pumping strategy to manage spatial–temporal variation of future land subsidence should be an integral part of flood risk management as it can sustain the effectiveness of the flood mitigation measures. [ABSTRACT FROM AUTHOR]

Rescue requests during large‐scale urban flood disasters can be difficult to validate and prioritise. High‐resolution aerial imagery is often unavailable or lacks the necessary geographic extent, making it difficult to obtain real‐time information about where flooding is occurring. In this paper, we present a novel approach to map the extent of urban flooding in Harris County, Texas during Hurricane Harvey (August 25–30, 2017) and identify where people were most likely to need immediate emergency assistance. Using Maximum Entropy, we predict the probability of flooding based on several spatially‐distributed physical and socio‐economic characteristics coupled with crowdsourced data. We compare the results against two alternative flood datasets available after Hurricane Harvey (i.e., Copernicus satellite imagery and riverine flood depths estimated by FEMA), and we validate the performance of the model using a 15% subset of the rescue requests, Houston 311 flood calls, and inundated roadways. We find that the model predicts a much larger area of flooding than was shown by either Copernicus or FEMA when compared against the locations of rescue requests, and that it performs well using both a subset of rescue requests (AUC 0.917) and 311 calls (AUC 0.929) but is less sensitive to inundated roads (AUC 0.721). [ABSTRACT FROM AUTHOR]

Two‐dimensional shallow water models are widely used tools for flood inundation mapping. However, even if High Performance Computing techniques have greatly decreased the computational time needed to run a 2D inundation model, this approach remains unsuitable for applications that require results in a very short time or a large number of model runs. In this paper we test a non‐parametric regression model based on least squares support vector machines as a computationally efficient surrogate of the 2D shallow water equations for flood inundation mapping. The methodology is initially applied to a synthetic case study consisting of a straight river reach flowing towards the sea. A coastal urban area is then used as a real test case. Discharge in three streams and tide levels are used as predictor variables to estimate the spatial distribution of maximum water depth and velocity in the study area. The suitability of this regression model for the spatial prediction of flood hazard is evaluated. The results show the potential of the proposed regression technique for fast and accurate computation of flood extent and hazard maps. [ABSTRACT FROM AUTHOR]

Coastal flood maps covering the whole European continent have become available in recent years. However, their ability to complement or replace high‐resolution local flood maps was not investigated so far. In this paper we compare pan‐European estimates of extreme sea levels and coastal flood extents at given return periods with observations and high‐resolution reference maps. The analysis is done for two pan‐European assessments and one global study. We find that whereas the models have good accuracy in estimating storm surge heights, large disparities exist between the large‐scale flood maps and four local maps of flood extents from England, the Netherlands, Poland, and France. Moreover, the accuracy of the underlying digital elevation model and assumptions about flood protection existing in a given area influence significantly the results. In addition, the first pan‐European projection of temporal trends in the size of flood zones is presented, with and without assuming flood protection levels. [ABSTRACT FROM AUTHOR]

Land use changes, landscape modifications and changing climate have resulted in local to regional flood risk increases in recent decades. As an alternative to traditional engineering approaches, there has been a movement towards catchment‐based flood risk management, a subset of which is natural flood management (NFM). NFM aims to enhance flood resilience through the slowing and storing of runoff and flow, based on the restoration and augmentation of hydrological and morphological catchment features. However, despite research highlighting their potential benefits, there is a limited quantity of robust and science‐based empirical evidence on how these structures function in the landscape and their efficacy in reducing flood hazards. To address this knowledge gap and contribute to the growing NFM evidence base, this study evaluates the efficacy of offline water storage ponds for flow attenuation. Two contrasting pond sites in the Tone and Parrett catchment headwaters (SW‐England) were monitored from April 2018 to December 2020 for channel flow, pond volume, and rainfall. Field‐scale, high resolution (1.61 cm spatial support) digital elevation models from Structure‐from‐Motion and manual surveys were collected to quantify pond dynamics and connectivity. A comprehensive, storm definition methodology was developed for event separation, to enable quantification of the impact of pond behaviour on stream flow, across storm hydrographs. Results show that where offline ponds function as designed, with direct pond filling from the channel, peak flow attenuation can reach 7% (maximum event AEP of 83%). Smaller events, where pond filling occurs directly from rainfall or runoff display only a maximum of 3% peak flow reduction (event AEP from 83% –>99%). The ability of ponds to attenuate flow is heavily reliant on sufficient structural conditions for ponds to fill directly from the channel and to drain slowly following event peaks. This study provides an empirical database for future NFM applications, including key criteria for future design and for use as observational data in modelling applications, by upscaling the efficacy of ponds to reduce flood impacts at larger scales. [ABSTRACT FROM AUTHOR]

We demonstrate that long‐term tidally induced changes in extreme sea levels affect estimates of major flood hazard in a predictable way. Long‐term variations in tides due to the 4.4 and 18.6‐year cycles influence extreme sea levels at 380 global tide gauges out of a total of 581 analyzed. Results show coherent regions where the amplitudes of the modulations are particularly relevant in the 100‐year return sea level, reaching more than 20 cm in some regions (western Europe, north Australia, and Singapore). We identify locations that are currently in a positive phase of the modulation and therefore at a higher risk of flooding, as well as when (year) the next peak of the long‐term tidal modulations is expected to occur. The timing of the peak of the modulation is spatially coherent and influenced by the relative importance of each cycle (4.4 or 18.6‐year) over the total amplitude. An evaluation of four locations suggests that the potentially flooded area in a 100‐year event can vary up to ∼45% (in Boston) as a result of the long‐term tidal cycles; however, the flooded area varies due to local topography and tidal characteristics (6%–13%). We conclude that tidally modulated changes in extreme sea levels can alter the potentially inundated area in a 100‐year event and that the traditional, fixed 100‐year floodplain is inadequate for describing coastal flood risk, even without considering sea‐level rise. Plain Language Summary: Interannual and decadal (long‐term) variations in tides modulate extreme sea levels, increasing the risk of flooding at specific and predictable times. Here, we use a data set of 581 tide gauges to estimate the magnitude of the long‐term tidally induced changes in extreme sea levels as well as to identify the timing of the peak of the modulations. We find significant amplitudes of the long‐term tidal modulations in extreme water levels. We conclude that the long‐term modulations in tides influence the total inundation area and, therefore, they should be taken into account when assessing coastal vulnerability. Key Points: Long‐term tidal cycles (4.4 and 18.6‐year) modulate extreme sea levels and affect estimates of flood riskThe timing of the peak of both modulations is influenced by the relative importance of each cycle over the total amplitudeTidally induced changes in extreme sea levels affect estimates of total inundation area [ABSTRACT FROM AUTHOR]

The identification of flood prone areas is essential for a range of engineering, risk reduction and research applications. Here, we describe a combined hydrological and hydraulic modelling approach for the assessment of flood‐prone areas and we present the results obtained over the Po river (Northern Italy). Runoff and river discharges are calculated through the hydrological model CHyM driven by GRIPHO, a new precipitation dataset for Italy. River flow data are used to obtain flood hydrographs for the CA2D hydraulic model, which calculates flood hazard maps at a resolution of 90 m. Flood simulations are run over a re‐shaped HydroSHEDS digital elevation model that includes information of the channel geometry. Modeled flood hydrographs are compared with observed data for a choice of gauging stations, showing a good performance of the CHyM model. We validate the flood hazard maps against observed flood events and official hazard maps. For high return periods, modelled maps can correctly identify up to 67% of the flood extent, both on the Po River and on smaller tributaries, while performances are more variable for lower return periods. Overall, the proposed approach suggests a strong potential for further applications, such as flood hazard assessment under future climate scenarios. [ABSTRACT FROM AUTHOR]

Understanding and modelling pluvial flood patterns is pivotal for the estimation of flood impacts in urban areas, especially in a climate change perspective. However, urban flood modelling under climate change conditions poses several challenges. On one hand, the identification and collection of climate change data suitable for flood‐related evaluations requires consistent computational and scientific effort. On the other hand, large difficulties can arise in the reproduction of the rainfall‐runoff transformation process in cases when only little information about the subsurface processes is known. In this perspective, a simplified approach is proposed to address the challenges regarding the quantitative estimation of climate change effects on urban flooding for real case applications. The approach is defined as "bottom‐up" because climate change information is not included in flood modelling, but it is only invoked for the interpretation of results. In other words, the challenge faced in this work is the development of a modelling strategy that is expeditious, because it does not require flood simulations for future rainfall scenarios, but only under current climate conditions, thus reducing the overall computational effort; and it is flexible, because results can be easily updated once new climate change data, scenarios or methods become available, without the need of additional flood simulations. To simulate real case applications, the approach is tested for a scenario analysis, where different return periods and hyetograph shapes are used as input for urban inundation modelling in Naples, Italy. The approach can support public and private stakeholders, such as land administrators and water systems managers; moreover, it represents a valuable and effective basis for climate change risk communication strategies. [ABSTRACT FROM AUTHOR]

Even though flooding is a threat to rural communities in plains drained by ephemeral rivers, the magnitude of its impact, coping/prevention mechanisms, and the implications for river management are not well known. In this study, data were collected using a phenomenological-based research design. Field observations, a questionnaire (n = 440), key informant interviews (10), and one focus group discussion (with seven discussants) were used to collect the desired data from flood-prone farmers. As the results show, 42% of the respondents believe that flooding has become stronger over the past 20 years, whereas 38% believe there has been no change. As mitigation measures, 52% of the respondents suggested evacuating to neighbouring villages as the best option. Most of the damage was experienced in farmlands (including crops, either harvested or standing) and settlements. As coping mechanisms, 31% of the respondents were displaced, whereas an additional 40% were forced to construct new houses for their settlement. Chi-square testing showed that the farmers' responses statistically varied among different groups (p < .001). In the meantime, community participation in flood control and catchment management is important. Improving flood management knowledge and the skills of different groups in a community is equally important. In this case, a qualitative inquiry approach was a good option to assess the hydrological conditions of rivers. [ABSTRACT FROM AUTHOR]

This study contributes a bathtub‐style inundation prediction model with abstractions of coastal processes (i.e., storm surge and wave runup) for flood forecasting at medium‐range (weekly to monthly) timescales along the coastline of large lakes. Uncertainty from multiple data sources are propagated through the model to establish probabilistic bounds of inundation, providing a conservative measure of risk. The model is developed in a case study of the New York Lake Ontario shoreline, which has experienced two record‐setting floods over the course of three years (2017–2019). Predictions are developed at a parcel‐level and are validated using inundation accounts from an online survey and flyover imagery taken during the recent flood events. Model predictions are compared against a baseline, deterministic model that accounts for the same processes but does not propagate forward data uncertainties. Results suggest that a probabilistic approach helps capture observed instances of inundation that would otherwise be missed by a deterministic inundation model. However, downward biases are still present in probabilistic predictions, especially for parcels impacted by wave runup. The goal of the tool is to provide community planners and property owners with a conservative, parcel‐level assessment of flood risk to help inform short‐term emergency response and better prepare for future flood events. [ABSTRACT FROM AUTHOR]

Extreme flood events are becoming more frequent and challenging due to climate change. Key objectives of this study are to evaluate different criteria used in assessing the hazard to people during flood events and, once determined, the most suitable method is then used to assess the hazard and the safest route(s) for evacuation during a flood event and for a particular case study. The results of the application of two criteria are analysed in terms of the flood hazard assessment with the two criteria being based on a widely used empirical approach and a mechanics based approach. Both criteria are used to assess the flood hazard to people during an extreme flash flood, which occurred on 16th August 2004 in Boscastle (UK). Results obtained for this study have highlighted that the mechanics based criteria are preferable in identifying the ideal escape routes, when considering the flood characteristics and the corresponding response of a human body. The main novelty of this study lies in linking the flood hazard rating with the human body characteristics, when determining the safest route and with a revised formula being developed, which includes the effects of ground slope in the application to a real case study. [ABSTRACT FROM AUTHOR]

This study examines whether catchment‐scale natural flood management (NFM) interventions could help to manage water levels in downstream urban watercourses and promote free discharge from surface drainage outfalls. A coupled modelling approach consisting of Dynamic TOPMODEL, HEC‐RAS, and Infoworks ICM models is used to characterise the response from a small Cambridgeshire catchment. Four different NFM scenarios (consisting of in‐channel woody debris and wider catchment afforestation) are defined. The attenuation of catchment response created by these measures is evaluated for an historic event and six different design storms. The consequent moderation of water depths at two downstream drainage outfalls is investigated with respect to maintaining free discharge from a surface drainage system. The case study results show that greatest reductions in the time of outfall inundation from NFM occur during frequent storm events (e.g., up to 5.75 hr during a 5‐year event). These reductions diminish with increasing storm severity but, by slightly desynchronising rural and urban responses, upstream interventions continue to have modest benefit for downstream drainage performance (e.g., preventing system capacity being exceeded during a 100‐year event). These results may interest water companies (increasingly involved in catchment‐scale NFM projects) looking to improve performance of surface water drainage. [ABSTRACT FROM AUTHOR]

The assessments of flood‐prone areas and flood risk due to pluvial flooding for Davao Oriental on Mindanao Island in the Philippines were carried out by the analytic hierarchy process (AHP) and maximum entropy (Maxent) models using multiple criteria such as slope, elevation, soil type, rainfall, drainage density, distance to the main channel, and population density. Flood records from 70 survey points were obtained and used to verify the model results. The criteria weights of the top three important factors in the AHP are rainfall (42%), slope (23%), and elevation (15%), whereas those in the Maxent model are elevation (36%), rainfall (23%), and soil (19%). The verification results show that the accuracies of the AHP and Maxent model are 81 and 95.6%, respectively, indicating that both approaches are reliable in flood hazard and risk assessments. Approximately 22% of the total area and approximately 30% of the total population of Davao Oriental are classified as high risk of pluvial flooding in the current situation by the AHP method. This study shows a broad‐scale high‐level data‐driven screening method that can be used to help identify potential hot spots for pluvial flooding for which more detailed numerical modelling studies should be undertaken. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) events are major drivers of compound flooding due to the interaction of wind‐driven storm surge and TC rainfall. Traditionally, coastal flood risk models have only taken into account surge flooding, even though it is known that the role of rainfall‐runoff is critical. There is limited understanding about the types of TC events that are capable of producing significant compounding and how site conditions at the coast affect the extent to which storm surge and rainfall‐runoff interact. This study investigates a suite of historical TCs making landfall near the Cape Fear River Estuary, NC, through a loosely coupled physical modeling methodology in order to draw conclusions about the spatial and temporal patterns of storm surge and rainfall that are able to induce significant compound impacts. Results indicate that intense outer rain bands falling over inland portions of the study area can be a driver of river‐surge compounding (increasing river levels by up to 0.36 m), while intense eyewall rainfall along the coast can result in localized compound impacts to coastal streams and tributaries if peak rainfall occurs near the time of peak storm tide. These localized compound impacts can result in defined interaction zones, where neither storm tide alone nor rainfall‐runoff alone can fully explain the observed maximum water levels. These results provide insight about the relative timing and spatial patterns of rainfall and storm surge that are capable of inducing compound flooding during TC events. Key Points: Compound flood impacts from historical TCs on North Carolina coast quantified through loosely coupled physical modeling methodSpatial overlap and relative timing between rainfall, peak river flows, and peak storm tide are critical factors in observed compoundingBoth outer rain bands and inner core rainfall from TCs can be drivers of compound flooding [ABSTRACT FROM AUTHOR]

Copyright of World Water Policy is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Existing major reservoirs in California, with average age above 50 years, were built in the previous century with limited data records and flood hazard assessment. Changes in climate and land use are anticipated to alter statistical properties of inflow to these infrastructure systems and potentially increase their hydrological failure probability. Because of large socioeconomic repercussions of infrastructure incidents, revisiting dam failure risks associated with possible shifts in the streamflow regime is fundamental for societal resilience. Here we compute historical and projected flood return periods as a proxy for potential changes in the risk of hydrological failure of dams in a warming climate. Our results show that hydrological failure probability is likely to increase for most dams in California by 2100. Noticeably, the New Don Pedro, Shasta, Lewiston, and Trinity Dams are associated with highest potential changes in flood hazard. Plain Language Summary: Dams are critical manmade infrastructure that provide resilience against extremes (e.g., droughts and floods) and regulate water resources. In 2017, California experienced a series of flooding events, which triggered incidents such as structural failure of the Oroville Dam's spillway. Because of the large social and economic impacts of such incidents and given the major dams in California have an average age of above 50 years, it is important to evaluate the risk of failure of dams over a planning period in the future. In this study, we inspected the possible impacts of climate change on the future flooding hazard for several major dams in California. Here we show that in the warmer future climate, the risk of dam failure most likely increases for most of the major dams in California. The insights gained from this study highlight the important role of adaptation strategies for the operational management of aging dams in a changing climate, together with adequate and timely maintenance. Key Points: Flood hazard is projected to increase at the upstream of major dams in California due to changes in precipitation extremesFailure probability is projected to increase for most of the California dams in a warming climateHistorical 100‐year flood is 5 times more likely for some biggest California dams under RCP8.5 (high greenhouse gas concentration levels) [ABSTRACT FROM AUTHOR]

Abstract: This study presents a novel methodology to estimate the impact of local sea level rise and extreme surges and waves in coastal areas under climate change scenarios. The methodology is applied to the Ebro Delta, a valuable and vulnerable low‐lying wetland located in the northwestern Mediterranean Sea. Projections of local sea level accounting for all contributions to mean sea level changes, including thermal expansion, dynamic changes, fresh water addition and glacial isostatic adjustment, have been obtained from regionalized sea level projections during the 21st century. Particular attention has been paid to the uncertainties, which have been derived from the spread of the multi‐model ensemble combined with seasonal/inter‐annual sea level variability from local tide gauge observations. Besides vertical land movements have also been integrated to estimate local relative sea level rise. On the other hand, regional projections over the Mediterranean basin of storm surges and wind‐waves have been used to evaluate changes in extreme events. The compound effects of surges and extreme waves have been quantified using their joint probability distributions. Finally, offshore sea level projections from extreme events superimposed to mean sea level have been propagated onto a high resolution digital elevation model of the study region in order to construct flood hazards maps for mid and end of the 21st century and under two different climate change scenarios. The effect of each contribution has been evaluated in terms of percentage of the area exposed to coastal hazards, which will help to design more efficient protection and adaptation measures. [ABSTRACT FROM AUTHOR]

In northern regions, river ice- jam flooding can be more severe than open-water flooding causing property and infrastructure damages, loss of human life and adverse impacts on aquatic ecosystems. Very little has been performed to assess the risk induced by ice-related floods because most risk assessments are limited to open-water floods. The specific objective of this study is to incorporate ice-jam numerical modelling tools (e.g. RIVICE, Monte-Carlo simulation) into flood hazard and risk assessment along the Peace River at the Town of Peace River (TPR) in Alberta, Canada. Adequate historical data for different ice-jam and open-water flooding events were available for this study site and were useful in developing ice-affected stage-frequency curves. These curves were then applied to calibrate a numerical hydraulic model, which simulated different ice jams and flood scenarios along the Peace River at the TPR. A Monte-Carlo analysis was then carried out to acquire an ensemble of water level profiles to determine the 1 : 100-year and 1 : 200-year annual exceedance probability flood stages for the TPR. These flood stages were then used to map flood hazard and vulnerability of the TPR. Finally, the flood risk for a 200-year return period was calculated to be an average of $32/m2/a ($/m2/a corresponds to a unit of annual expected damages or risk). Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recent advances have been made to modernize estimates of probable precipitation scenarios; however, researchers and engineers often continue to assume that rainfall events can be described by a small set of event statistics, typically average intensity and event duration. Given the easy availability of precipitation data and advances in desk-top computational tools, we suggest that it is time to rethink the 'design storm' concept. Design storms should include more holistic characteristics of flood-inducing rain events, which, in addition to describing specific hydrologic responses, may also be watershed or regionally specific. We present a sensitivity analysis of nine precipitation event statistics from observed precipitation events within a 60-year record for Tompkins County, NY, USA. We perform a two-sample Kolmogorov-Smirnov (KS) test to objectively identify precipitation event statistics of importance for two related hydrologic responses: (1) peak outflow from the Six Mile Creek watershed and (2) peak depth within the reservoir behind the Six Mile Creek Dam. We identify the total precipitation depth, peak hourly intensity, average intensity, event duration, interevent duration, and several statistics defining the temporal distribution of precipitation events to be important rainfall statistics to consider for predicting the watershed flood responses. We found that the two hydrologic responses had different sets of statistically significant parameters. We demonstrate through a stochastic precipitation generation analysis the effects of starting from a constrained parameter set (intensity and duration) when predicting hydrologic responses as opposed to utilizing an expanded suite of rainfall statistics. In particular, we note that the reduced precipitation parameter set may underestimate the probability of high stream flows and therefore underestimate flood hazard. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The provinces of northern Iran that border the Caspian Sea are forested and may be prone to increased risks of flooding due to deforestation and other land use changes, in addition to climate change effects. This research investigated changes in runoff from a small forested catchment in northern Iran for several land use change scenarios and the effects of higher rainfall and high antecedent soil moisture. Peak discharges and total runoff volumes from the catchment were estimated using the U.S. Soil Conservation Service "Curve Number" (SCS‐CN) method and the SCS dimensionless unit hydrograph. This method was selected for reasons of data availability and operational simplicity for flood managers. A geographical information system (GIS) was used to manipulate spatial data for use in the catchment runoff modelling. The results show that runoff is predicted to increase as a result of deforestation, which is dependent on the proportion of the catchment area affected. However, climate change presents a significant flood hazard even in the absence of deforestation. Other land use changes may reduce the peak discharges of all return period floods. Therefore a future ban on timber extraction, combined with agricultural utilisation of rangeland, could prove effective as "nature‐based" flood reduction measures throughout northern Iran. [ABSTRACT FROM AUTHOR]

There is increasing attention for the robustness of systems, in view of more frequent and more extreme weather events. Calls to increase a system's robustness are usually motivated by the resulting reduced sensitivity to extreme events and uncertainties about their probability of occurrence. The concept has been elaborated for flood risk systems, but recently questions have arisen about whether subsystems, such as flood defences or rivers, should and could also be assessed on their robustness. Against the background of a recent debate in the Netherlands about whether to raise the embankments again or to make more room for the rivers in anticipation of increasing extreme river discharges into the future, we propose to define the robustness of embanked alluvial rivers by their sensitivity to uncertainties in flood discharge, expressed by the relationship between discharge and flood water level. We assess the Rhine River branches and Meuse River in the Netherlands and show how their planform, as defined by the location of the embankments and the presence of obstacles in the floodplains, causes remarkable differences in robustness per river and per river stretch. We finally discuss what this might entail for policy planning. [ABSTRACT FROM AUTHOR]

River flooding is among the most destructive of natural hazards globally, causing widespread loss of life, damage to infrastructure and economic deprivation. Societies are currently under increasing threat from such floods, predominantly from increasing exposure of people and assets in flood‐prone areas, but also as a result of changes in flood magnitude, frequency, and timing. Accurate flood hazard and risk assessment are therefore crucial for the sustainable development of societies worldwide. With a paucity of hydrological measurements, evidence from the field offers the only insight into truly extreme events and their variability in space and time. Historical, botanical, and geological archives have increasingly been recognized as valuable sources of extreme flood event information. These different archives are here reviewed with a particular focus on the recording mechanisms of flood information, the historical development of the methodological approaches and the type of information that those archives can provide. These studies provide a wealthy dataset of hundreds of historical and palaeoflood series, whose analysis reveals a noticeable dominance of records in Europe. After describing the diversity of flood information provided by this dataset, we identify how these records have improved and could further improve flood hazard assessments and, thereby, flood management and mitigation plans. This article is categorized under: Science of Water > Water QualityEngineering Water > Planning WaterScience of Water > Methods Historical, botanical and geological archives offer unique insight into truly extreme flood events and their variability in space and time, thanks to the long timeframe they document. The evidence contained within these underutilized archives has the potential to improve flood hazard assessments that are crucial for the sustainable development of societies. [ABSTRACT FROM AUTHOR]

Bridges are in direct interaction with the environment and thus are exposed to various natural hazards such as earthquakes and floods, that may result in severe damage and substantial direct and indirect losses. The multiple hazard events may be subsequent single events (e.g., a flood event followed by an earthquake) or combined multi‐hazard events (e.g., cascading ground failure event after an earthquake). The effect of multiple hazards on bridge fragility is related to the damage level of the bridge components and the associated failure mechanisms that may compromise the roadway network functionality. The scope of this work is to propose an approach for the multiple‐hazard assessment of bridges considering subsequent events and different damage scenarios of critical bridge components, i.e. piers, bearings and abutments. Therefore, the effect of the damage level of critical bridge components and their interdependence on the fragility assessment for subsequent hazard events is investigated. Different damage scenarios and hazard sequences are studied, providing insight into the damage mechanisms and the accumulation of damage. The approach is applied to the multiple hazard assessment of a case study typical riverine bridge in Greece and the results are comparatively discussed. [ABSTRACT FROM AUTHOR]