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Frequent floodings in Semarang City have generated increasing damages and losses in property and life quality. The cause of flooding is related to the coupled impacts of land subsidence, hydraulics hazards along with poor drainage and water retention systems. This paper studies the most recent flooding hazards caused by hydrological origins (i.e., river discharge, tidal) and land subsidence. In the study, riverine origin of flooding is simulated with the help of HEC-RAS 2D, while the tidal origin is simulated to high highest water level. However, due to the absence of the most recent topographic data, the role of land subsidence is measured by estimating the vertical changes of digital elevation model taken from Sentinel 1A. Flooding extent, in terms of depth and coverage, is verified based on satellite imagery Sentinel-2 which is cloud-processed using Google Earth Engine (GEE) and field survey. Fluvial flood is simulated with several boundary condition scenarios using combinations of 5-, 25-, or 50-year return periods of flood which is integrated with mean sea level (MSL) or high highest water level (HHWL) tides. Those boundary conditions are then incorporated into different terrains, namely LiDAR, DEMNAS, and TerraSAR DEM, to see how different digital elevation models (DEMs) can impact model sensitivity. By overlaying model outputs and land cover map, it can be concluded that settlements and water bodies are among the most potentially affected areas, covering up to 17 km2. This study is expected to help policymakers make a primary assessment of combined tidal and fluvial flood hazard through mitigation and adaptation measures. [ABSTRACT FROM AUTHOR]

Settlements situated downstream of hills and dams are invariably at risk of floods. Constant land use/land cover changes in the Vishwamitri Watershed and long-term climate variability have made Vadodara City more susceptible to river flooding in recent times. In the past, the local government authorities have only tried to solve this issue within the administrative boundary of the Vadodara City. This study demonstrates the importance of watershed scale investigation over administrative scale. The study presents a review of the current flooding and environmental degradation challenges that are affecting the Vishwamitri Watershed. For the analysis, the entire watershed was classified into two parts: (1) the upper watershed and (2) city limits. The data-deficient upper watershed was studied with the aid of site visits and secondary sources. The floodplain within the city limits was simulated for the 2005 peak discharge event (805 cumec) using Hydrological Engineering Centre—River Analysis System (HEC-RAS, 5.0.7.) software and HEC-GeoRAS (10.2.) (a set of procedures, tools, and utilities for processing geospatial data in ArcGIS using a graphical user interface). The simulated water surface elevation from HEC-RAS was validated with the in situ data available within the city limits. The generated floodplain extent map was used for conducting a primary flood impact survey and analysing the inundation-affected zones. Various aspects of the flood plain, like land use, land cover, built form, affected demography, river system, natural environment and habitat, were analysed during this survey. For the mitigation of floods and other maladies associated with the watershed, this probing calls for the restoration of the river ecosystem back to its original state to the maximum possible extent. Nature-based solutions were found to be the remedy for most of the issues pertaining to the floodplain. The study can potentially help concerned stakeholders of any flood-prone urban settlement to envision the issue of flooding with the whole river system and watershed in mind. This will discourage the usual approach of interventions limited to administrative boundaries. [ABSTRACT FROM AUTHOR]

River (fluvial), surface water (pluvial) and coastal flooding pose a significant risk to the United Kingdom. Therefore, it is important to assess flood risk particularly as the impacts of flooding are projected to increase due to climate change. Here we present a high resolution combined fluvial and pluvial flood susceptibility map of England. This flood susceptibility model is created by using past flood events and a series of meaningful hydrological parameters to a training machine learning model. We tested the relative performance of different machine learning algorithms, including Classification and Regression Trees, Random Forest and XGBoost and found the XGBoost performed the best, with an area under the receiver operating characteristic ROC Curve (AUC) of 0.93. We also found the model performed well on unseen areas, and we discuss the possibility of extending to regions that has no information on past flood events. Additionally, to aid in understanding what factors may impact flood risk to a particular area, we used Shapley additive explanations which allowed us to investigate the sensitivity of the predicted flood probability to flood factors at a given location. [ABSTRACT FROM AUTHOR]

Abstract River (fluvial), surface water (pluvial) and coastal flooding pose a significant risk to the United Kingdom. Therefore, it is important to assess flood risk particularly as the impacts of flooding are projected to increase due to climate change. Here we present a high resolution combined fluvial and pluvial flood susceptibility map of England. This flood susceptibility model is created by using past flood events and a series of meaningful hydrological parameters to a training machine learning model. We tested the relative performance of different machine learning algorithms, including Classification and Regression Trees, Random Forest and XGBoost and found the XGBoost performed the best, with an area under the receiver operating characteristic ROC Curve (AUC) of 0.93. We also found the model performed well on unseen areas, and we discuss the possibility of extending to regions that has no information on past flood events. Additionally, to aid in understanding what factors may impact flood risk to a particular area, we used Shapley additive explanations which allowed us to investigate the sensitivity of the predicted flood probability to flood factors at a given location.

Fluvial floods endure as one of the most catastrophic weather-induced disasters worldwide, leading to numerous fatalities each year and significantly impacting socio-economic development and the environment. Hence, the research and development of new methods and algorithms focused on improving fluvial flood prediction and devising robust flood management strategies are essential. This study explores and assesses the potential application of 1D-Convolution Neural Networks (1D-CNN) for spatial prediction of fluvial flood in the Quang Nam province, a high-frequency tropical cyclone area in central Vietnam. To this end, a geospatial database with 4156 fluvial flood locations and 12 flood indicators was considered. The ADAM algorithm and the MSE loss function were used to train the 1D-CNN model, whereas popular performance metrics, such as Accuracy (Acc), Kappa, and AUC, were used to measure the performance. The results indicated remarkable performance by the 1D-CNN model, achieving high prediction accuracy with metrics such as Acc = 90.7%, Kappa = 0.814, and AUC = 0.963. Notably, the proposed 1D-CNN model outperformed benchmark models, including DeepNN, SVM, and LR. This achievement underscores the promise and innovation brought by 1D-CNN in the realm of susceptibility mapping for fluvial floods. [ABSTRACT FROM AUTHOR]

Given the dynamics of climate events (hazards) and their linkages to human health, it is imperative to continuallly check the impacts of these events on the public health system. While efforts have been made to understand fluvial flood and COVID-19 vulnerability and impacts, substantial gaps about impacts of their simultaneous occurrence on densely-populated communities abound. This paper presents an assessement of the occurrence of fluvial flooding and its potential to undermine the management of the COVID-19 pandemic in Lagos State, Nigeria. This study applied the indicator-based risk assessment method to determine the pattern of COVID-19 risk in the study area. Flood hazard and health facilities datasets of Lagos State were also used to determine the flood extent and pattern of floodexposed health facilities in ArcGIS 10.7.1. Results revealed that Apapa, Eti Osa, Ibeju Lekki, Mushin, and Lagos Mainland local government areas (LGAs) were at a very high risk of COVID-19. Results also highlight six LGAs that should be prioritized in managing COVID-19 due to the exposure of the majority of its health facilities to flood. Far-reaching recommendations on the need to prioritize these floodexposed health facilities for COVID-19 risk reduction, humanitarian aid and prevention strategies is made. Also, future research in the study area should explore sustainable strategies to adapt to COVID-19 and flood events from an interdisciplinary perspective

Settlements situated downstream of hills and dams are invariably at risk of floods. Constant land use/land cover changes in the Vishwamitri Watershed and long-term climate variability have made Vadodara City more susceptible to river flooding in recent times. In the past, the local government authorities have only tried to solve this issue within the administrative boundary of the Vadodara City. This study demonstrates the importance of watershed scale investigation over administrative scale. The study presents a review of the current flooding and environmental degradation challenges that are affecting the Vishwamitri Watershed. For the analysis, the entire watershed was classified into two parts: (1) the upper watershed and (2) city limits. The data-deficient upper watershed was studied with the aid of site visits and secondary sources. The floodplain within the city limits was simulated for the 2005 peak discharge event (805 cumec) using Hydrological Engineering Centre—River Analysis System (HEC-RAS, 5.0.7.) software and HEC-GeoRAS (10.2.) (a set of procedures, tools, and utilities for processing geospatial data in ArcGIS using a graphical user interface). The simulated water surface elevation from HEC-RAS was validated with the in situ data available within the city limits. The generated floodplain extent map was used for conducting a primary flood impact survey and analysing the inundation-affected zones. Various aspects of the flood plain, like land use, land cover, built form, affected demography, river system, natural environment and habitat, were analysed during this survey. For the mitigation of floods and other maladies associated with the watershed, this probing calls for the restoration of the river ecosystem back to its original state to the maximum possible extent. Nature-based solutions were found to be the remedy for most of the issues pertaining to the floodplain. The study can potentially help concerned stakeholders of any flood-prone urban settlement to envision the issue of flooding with the whole river system and watershed in mind. This will discourage the usual approach of interventions limited to administrative boundaries.

Fluvial floods can cause significant damages and are expected to increase in magnitude and frequency throughout the twenty-first century due to global warming. Alongside hazard characteristics, damage potentials depend on exposure and vulnerability, which are changing in the wake of socio-economic developments. In the context of continuously evolving damage-causing factors, assessments of future changes in flood damage potentials are increasingly asked for by decision-makers in flood risk management. This study addresses this need by (a) providing a systematic review of contemporary assessment approaches to quantitatively compare direct economic losses from fluvial flooding under current and future conditions and (b) combining the reviewed approaches to an applicable methodology which is used in a case study to quantify changing flood damage potentials in the Neckar River basin in southern Germany. Therefore, a scoping study of contemporary flood damage assessment approaches supported by geographic information systems (GIS) is performed. The subsequent case study of the Neckar River prognoses a significant increase in average annual flood damages in the study area throughout the twenty-first century. The case study produces valid results with regards to current precipitation data, whereas the absence of verification data makes the validation of projected scenarios more difficult. To account for uncertainties surrounding these future projections, a nascent qualitative confidence estimation is introduced to reflect on the strength of knowledge underlying the used flood damage assessment methodology. [ABSTRACT FROM AUTHOR]

The problem of flood vulnerability has been reviewed in several studies, however, the reviews focused exclusively either on the social or on the physical component of the problem. The components of flood vulnerability are interdependent and each of them makes an equally important contribution to the flood vulnerability index. This study identifies and evaluates the integrated flood vulnerability index (FVI) of an area by considering its multiple components (social, economic, and environmental). The Analytic Hierarchy Process (AHP) method was applied to evaluate the weight of each component. The evaluation was based on the judgements of experts working at local government policymaking agencies. The input data for the AHP were acquired through a questionnaire survey. Eleven indicators that delivered significant results were then selected. The FVI results show high flood vulnerability at the local scale. The FVI provides the basis for the identification of villages with high vulnerability indices. The results provide essential information about pluvial flood vulnerability at the local scale, about the area with the highest vulnerability index, and the most vulnerable villages. The results also show that the components that have a significant impact on the flood vulnerability index include environmental components (43.4%), social components (28.5%), and physical components (28.1%). [ABSTRACT FROM AUTHOR]

The integrative approach of water, energy, and food nexus (WEF nexus) is now widely accepted to offer better planning, development, and operation of these resources. This study presents a first attempt towards understanding the WEF nexus of urban environments in the Nile River Basin under conditions of hydrological droughts and fluvial floods. A case study was conducted for the capital of Sudan, Khartoum, at the confluence of the White Nile and the Blue Nile for illustration. The results were based on analyses of river flow and water turbidity data, field observations, a printed questionnaire and an interview of farmers practicing irrigated agriculture, and hydropower modeling. The study analyzes indicators for the association of the river water resources environment (intra-annual regime, quantity, and quality), the status of urban irrigated agriculture, water treatment for domestic use, and hydropower generation under hydrological extremes, i.e. droughts and fluvial floods. It additionally examines the consequent interactions between the impacts on three sectors. The present study shows how floods and droughts impose impacts on seasonal river water quality and quantity, water treatment for domestic use, irrigated agriculture, and hydro-energy supply in an urban environment. The results demonstrate how the two hydrological phenomena determine the state of hydropower generation from dams, i.e. high energy production during floods and vice versa during droughts. Hydropower dams, in turn, could induce cons in the form of low fertile soils in the downstream due to sediment retention by the reservoir. Finally, present and potential options to minimize the above risks are discussed. This study is hoped to offer good support for integrated decision making to increase the resource use efficiency over the urban environment within the Nile Basin. [ABSTRACT FROM AUTHOR]

The mechanisms of fluid mud formation and its characteristics are far from clear in the deep-dredged waterway in Xiamen estuarine bay. Some experiments were conducted in the muddy estuarine bay of Xiamen when Super Typhoon Meranti, which was the strongest typhoon to have affected the area over the last 70 years, struck and after it passed. Contrary to expectation, results reveal that typhoon-induced waves are not the main hydrodynamic forcing that transport sediment. The influence of fluvial flooding and ebb tidal flow results in high concentrations (greater than 14 kg/m3) of suspended sediment in a layer near the bed, which may either deposit or be released directly into the waterway to form fluid mud. Further, new indicators are proposed, namely, river discharge and fluvial flood duration, to describe quantitatively the conditions under which fluid mud forms; it is in fact likely to form in the waterway when a discharge greater than 1,000 m3/s lasts for more than one day. The new indicators may be applied as reference by waterway administrators in their operations. [ABSTRACT FROM AUTHOR]

The identification and classification of critical coastal areas is becoming more and more important from a coastal management point of view, especially considering future climate change. The standardized assessment of multiple hazards and their potential impacts is crucial, in terms of risk management, for those coastal areas where both marine and fluvial hazards can occur. Nevertheless, in Bocca di Magra (Liguria Region, Italy), where both coastal and fluvial flooding can occur, up until now the potential impacts from marine flooding have not been thought to be of importance; only the impact of fluvial flooding has been systematically analysed. Now, however, the Liguria Regional stakeholders have become interested in understanding the potential impact of marine inundations compared to fluvial inundations, applying the CRAF (Coastal Risk Assessment Framework) methodology developed inside the RISC-KIT project. The hazard modelling of coastal and fluvial inundations was used, together with exposure data, to evaluate the direct and systemic impacts generated by both flooding mechanisms separately. An End-User-driven Multi-Criteria Analysis was implemented to compare coastal and fluvial impacts on the same area. For an event with a 1 in 200 year return period, the CRAF predicts that fluvial inundation generates higher impacts, in comparison to the marine one. Even though the impacts in the coastal area are less, the impacted exposed elements are different from those impacted by fluvial inundation and none of them can be excluded from the analysis. This work highlights the need for regional managers to develop combined coastal-fluvial flooding assessments; such actions should be seen as a priority for flood disaster risk management in locations affected by both marine flooding and riverine flash flooding. [ABSTRACT FROM AUTHOR]

High aggradation and degradation in a river induced by last flood event will respectively raise and decrease the risk of an upcoming flood event. However, this point is likely to be ignored or is not fully considered in some 2D fluvial flood models. To address this problem, this work develops a 2D high-resolution hydrodynamic model coupled with the sediment transport and the river bed evolution models. The modelling system is within the framework of a Godunov-type finite volume scheme. GPU technique is applied to accelerate the computation by more than 10 times, comparing to the CPU counterpart. After being validated against an experimental benchmark test, the model is applied to simulate the effects of the morphological change on flood patterns for the Bayangaole Reach of Yellow River, China. The results indicate that the effect of perturbed bed could be of significance for the fluvial flood over movable bed. It is therefore suggested to take into account when evaluating the flood risk in this case. [ABSTRACT FROM AUTHOR]

This investigation evaluates the effects of hydrological uncertainty in the results of flood extent estimates during the incidence of a tropical storm. For this, the methodology is comprised of field measurements, elevation data, a distributed hydrological model and a standard two-dimensional numerical model. Uncertainty is considered in the distributed hydrological model through the estimation of possible hydrographs from precipitation data registered during the incidence of an extreme event. The characterisation of the run-off by multiple possibilities opens the door to a probabilistic estimation of flood maps, enabling the consideration of hydrological uncertainties and their propagation to an estimated flood extension. It is shown that during the incidence of the tropical storm Arlene, the estimated flooded area is similar to what was registered by satellite imagery. Although the methodology does not consider all the uncertainties that may be involved in the determination of a flooded area, it is reflected that it favours the preventive action in the generation of flood management strategies. The selected approach is a first iteration in the production of a fully quantified approach to the analysis of flood risk, especially where there are doubts about how the catchment responds to a given extreme precipitation event. [ABSTRACT FROM AUTHOR]

Summary: Conventional techniques for quantifying and then managing flood risks are invalid under ‘non-stationary’ climate conditions. Trend detection and attribution are problematic given that the outcome depends on the start and end date of the record, choice of index and test statistic, assumed behaviour of the system, and many non-climatic confounding factors. Analyses are further hampered by short and non-homogeneous flow records. In this paper, we use an objective weather classification scheme to reconstruct the atmospheric drivers of fluvial flood occurrence and magnitude in England, Scotland and Wales since the 1870s. We demonstrate the index using long (>50year) annual maximum (AMAX) and peak over threshold (POT) flood records for 114 stations. Synoptic indices show modest skill at hindcasting multi-decadal variations in flood frequency at national, regional and catchment scales, but not for flood magnitudes. Flood rich episodes are identified in the periods 1908–1934, 1977–1988 and from 1998 onwards. We find that five weather types account for 68% of flood occurrence, and just three types were linked to the most widespread winter floods. These flood-generating systems generally show no sustained changes in frequency, persistence, relative contribution, or rain-bearing properties since the 1930s. However, there are emergent patterns in the day-to-day persistence (declining) and mean precipitation yield (rising) of anticyclonic weather types that merit further investigation. Based on our evaluation, we recommend use of objective weather indices derived from observed atmospheric pressure patterns when interpreting fluvial flood risk linked to climate drivers. [Copyright &y& Elsevier]

This investigation presents an integrated study for the identification of coastal and fluvial forcing, in the generation of flood events in the lower area of the Tonalá River. The methodology is designed to reduce some of the uncertainties in the results and is comprised by high-quality field measurements, a two-dimensional numerical model and light ranging and detection data. Under typical conditions, results show good agreement between numerical and measured data. Investigation of mesh resolution effects and roughness parameterisation along the floodplain demonstrates the grid independence of the results and enabled the selection of a realistic roughness value for the floodplain. Results imply a sensitivity of the region to the combined river and coastal forcing. This study demonstrates that a good description of the terrain elevation, acquisition of high-quality bathymetric data and proper calibration of the roughness parameters provide the adequate set-up for the identification of vulnerable areas to flood events generated by river discharges and storm surges. The combined scenarios of high discharges and storm surges showed a delicate balance between river and coastal fluxes within this system. The approach could be useful for both, the generation of flood management strategies and the understanding of the role of driving physical processes. [ABSTRACT FROM AUTHOR]

• Two surveys were conducted to estimate flood impacts on environments in estuary. • Salinity/nitrate persisted, but phosphate/chlorophyll recovered rapidly after flood. • Dam improves the dissolved oxygen condition, but the flood can enhance hypoxia. Land-ocean interaction plays an essential role in the transport fate of terrestrial matters in the coastal and shelf regions. Flood discharge from a mega river, containing massive water, sediment, and nutrient loads, could result in substantial and complex impacts on the physical and biogeochemical dynamics of coastal systems. In this study, field campaigns were conducted in a region from the Changjiang River Estuary to the East China Sea (ECS) before and after a significant flood. The impacts of the flood on physical and biogeochemical environments were assessed. The results revealed that the fluvial flood enhanced the offshore expansion of the low-salinity river plume and associated sediment/nutrient fronts. However, the area of elevated chlorophyll-a at the river mouth did not expand noticeably. A numerical model was applied to quantify the contribution of the Three Gorges Dam (TGD) to the spatial intensity and temporal duration of fluvial flood effects on estuary–shelf continuum. The results predicted a maximum of 2° latitudinal offshore displacement of the shelf water. Salinity and nitrate exhibited conservative expansions, with a longer relaxation time (~2 months) than chlorophyll-a and phosphate. After the TGD-regulated flow event ceased, salinity and nitrate effects persisted, but phosphate and chlorophyll-a recovered rapidly. The flood decreased the dissolved oxygen (DO) concentration around the river mouth and the offshore region, but not in the nearshore transient area. In contrast, the non-TGD regulation increased the regional DO concentration, which reduced the hypoxia risk. The TGD has become a crucial anthropogenic driver of environmental changes in the Changjiang Estuary-ECS continuum. [ABSTRACT FROM AUTHOR]

• Coarsening Digital Elevation Model (DEM) resolution reduces river channel conveyance, resulting in overprediction of flood. • Resolution of DEM for flood modelling needs to be at least finer than the modelled river width. • DEM fusion presented in this study can be a cost-effective way of obtaining fit for purpose 2D flood maps. With the extensive use of 2D flood models, the resolution and quality of Digital Elevation Models (DEMs) have come under greater focus especially in urban hydrology. One of the major research areas, in this regard, is the effect of DEM resolution on flood modelling. This study first investigates the root causes of the impact of DEM resolution on urban fluvial flood modelling outputs using DEMs with grid resolutions ranging from 1 m to 50 m. The study then investigates how DEM resolution affects the definition and characterisation of the river channel and the consequences of this for the modelled results. For this purpose, a separate set of merged DEMs was generated where the river channel as defined by the 1 m resolution DEM is merged with coarser resolution DEMs. Data obtained during the flood event caused by Storm Desmond (2015) in Cockermouth (Cumbria, UK) was used for this study. The HEC-RAS 2D model was used for all of the simulations. The benchmark model obtained with the 1 m resolution DEM was calibrated using measured water levels at two locations within the rivers. Results show that there is a 30% increase in flood extent from 58.9 ha to 79.0 ha and a 150% increase in mean flood depth from 1.74 m to 4.30 m when the resolution reduces from a 1 m grid to a 50 m grid. The main reason for this is the increasing lack of definition of the river channel with an associated reduction in the estimated depth of the river resulting in reduced river channel conveyance. This then leads to an increase in the flood extent and depth especially in the immediate vicinity of the river. This effect is amplified when the DEM grid size is greater than the river width. When the 1 m resolution DEM for the river channel is used in conjunction with coarser resolution DEMs for the surrounding areas (merged DEMs), there is a significant improvement in the agreement between the modelled and the reference case (obtained from the benchmark model) flood extents and depths. The use of merged DEMs reduces the error in mean flood depth from 90% to 4% and reduces the overall RMSE in flood depths from 2.6 m to 0.9 m at 30 m resolution. The use of merged DEMs, where a higher resolution DEM is used to characterise the river channel in conjunction with, for example, a 30 m resolution DEM (e.g., the freely available NASA Shuttle Radar Topography Mission DEMs) for the wider area could be a cost-effective solution for locations where higher resolution DEMs may not be available. [ABSTRACT FROM AUTHOR]

Urban flooding is a severe and pervasive hazard caused by climate change, urbanization, and limitations of municipal drainage systems. Cities face risks from different types of floods, depending on various geographical, environmental, and hydrometeorological conditions. In response to the growing threat of urban flooding, a better understanding of urban flood vulnerability is needed. In this study, a comprehensive method was developed to evaluate the vulnerability of different types of urban floods. First, a coupled urban flood model was built to obtain the extent of influence of various flood scenarios caused by rainfall and river levee overtopping. Second, an assessment framework for urban flood vulnerability based on an indicator method was used to evaluate the vulnerability in different flood hazard scenarios. Finally, the method was applied to Lishui City, China, and the distribution and pattern of urban flood vulnerability were studied. The results highlight the spatial variability of flooding and the vulnerability distributions of different types of urban floods. Compound floods were identified to cause more severe effects in the urban areas. [ABSTRACT FROM AUTHOR]

Vulnerability assessment is an essential tool in mitigating the impact of urban flooding. To date, most flood vulnerability research has focused on one type of flood, such as a pluvial or fluvial flood. However, cities can suffer from urban flooding for several reasons, such as precipitation and river levee overtopping. Therefore, a vulnerability assessment considering different types of floods (pluvial floods, fluvial floods, and compound flooding induced by both rainfall and river overtopping) was conducted in this study. First, a coupled urban flood model, considering both overland and sewer network flow, was developed using the storm water management model (SWMM) and LISFLOOD-FP model to simulate the different types of flood and applied to Lishui, China. Then, the results of the flood modeling were combined with a vulnerability curve to obtain the potential impact of flooding on different land-use classes. The results indicated that different types of floods could have different influence areas and result in various degrees of flood vulnerability for different land-use classes. The results also suggest that urban flood vulnerability can be underestimated due to a lack of consideration of the full flood-induced factors. [ABSTRACT FROM AUTHOR]

• A large ensemble climate simulation dataset was applied to flood risk assessment. • Pluvial and fluvial flood risk curves were derived without probabilistic modelling. • Pluvial flood risk was comparable with fluvial flood risk in the study area. • Fluvial flood causes deeper flood depths while pluvial flood more widely expands. • Pluvial flood needs more attention in low-lying urban areas. Flood disasters are caused by two types of flooding: pluvial and fluvial flooding. The different hydrodynamic characteristics of these two types have been intensively discussed in a literature. However, their impact and the resulting damage have not yet been examined in a comprehensive manner due to the lack of extreme rainfall data and/or computational costs of flood simulations. Recently, an increasing number of ensemble climate simulation data has become available, providing long-term rainfall data based on numerical climate simulations. This is a case study of a flooding in an urban area set in Nagoya City, Japan. We applied a large ensemble climate simulation database, d4PDF, to a pluvial and fluvial flood model and derived the flood risk curves for each type of flooding. The results indicated that pluvial flooding presents comparable economic risk to fluvial flooding (only 16% and 17% lesser damage at 50- and 100-year return periods, respectively) despite its significantly shallower flood depths (area with flood depth over 45 cm was only 10.5% and 5.4%, respectively). The significant impact of pluvial flooding is attributable to its wider flood area (despite shallower depths), impacting major economic assets sprawled over the city, including areas further away from the river. Furthermore, fluvial flood risk was managed by settling the Nagoya Castle (now the central economic district) on higher altitudes. The results suggest that pluvial flooding could have comparable economic risks to fluvial flooding in urban areas where major economic assets are not concentrated around streams as well as historical countermeasures are installed against fluvial flooding. [ABSTRACT FROM AUTHOR]

International aid for climate change adaptation in West Africa is increasing exponentially, but our understanding of hydroclimatic risks is not keeping pace with that increase. The aim of this article is to develop a multihazard risk assessment on a regional scale based on existing information that can be repeated over time and space and that will be useful during decision-making processes. This assessment was conducted in Dosso (Niger), the region most hit by flooding in the country, with the highest hydroclimatic risk in West Africa. The assessment characterizes the climate, identifies hazards, and analyzes multihazard risk over the 2011–2017 period for each of the region's 43 municipalities. Hazards and risk level are compared to the intervention areas and actions of 6 municipal development plans and 12 adaptation and resilience projects. Over the past seven years, heavy precipitation and dry spells in the Dosso region have been more frequent than during the previous 30-year period. As many as 606 settlements have been repeatedly hit and 15 municipalities are classified as being at elevated-to-severe multihazard risk. The geographical distribution of the adaptation and resilience projects does not reflect the risk level. A third of the local development plans examined propose actions that are inconsistent with the main hydroclimatic threats. [ABSTRACT FROM AUTHOR]