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Active surface deformation, displacement pattern, and erosional variability is estimated using the geomorphologically sensitive morphometry along with the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique using the Sentinel-1Adata (119 images) acquired between 07- 02-2017 and 10-02-2021. The average velocities for this dataset are estimated to be between ±11 mm/y. The Raunthi River catchment from where the flood was triggered is undergoing ~8 mm/y subsidence and ~10 mm/y uplift. Compared to this the basin wide deformation (Rishi Ganga basin) is estimated to be around ±10 mm/y with commulative ground displacement of around ±45 mm. The times series analysis suggests an increase in the ground displacement by around 5 mm/y and seems to be responsible for the expansion of pre-existing cracks in the vicinity of the Vaikrita Thrust (VT) and subsequent failure of the northern face of Nandi Peak on 7th February 2021. The Global Positioning System (GPS) derived strain distribution pattern indicate a relatively higher accumulation of strain (>0.35µ strain/y). The normalized steepness index (ksn) variation along the longitudinal section of Rishi Ganga and Raunthi River sub-basin in Central Himalayan region shows anomalous increase at the glacio-fluvial transitional processes. Moreover, the χ profiles as well as planform plots shows anomalously lower values within the Raunthi River sub-basin when compared with the Rishi Ganga basin. Based on the lower values of χ it is observed that Raunthi River sub-basin is undergoing high erosion which can be caused by the presence of sheared lithology and incision of the relict glacial and paraglacial sediments. We negate the suggestion that abrupt rise in the temperature was the major triggering mechanism for the recent disaster, instead it is the sheared lithology and pre-existing fissure developed because of differential uplift and subsidence in Raunthi River that led to the wedge failure and subsequent flash flood. Had the climate was the major driver of the recent tragedy ?, it should have impacted multiple hanging glaciers in the Rishi Ganga valley. Therefore, the study calls for detailed geomorphological, structural and glaciological investigation in regions dominated by glacial and paraglacial processes in the strategic regions of the Himalaya. Towards this, the state of art PSInSAR technique seems to provide fast and reliable detection of terrain instability/stability along with identification of potential areas of slope failures in near future in the glacial and preglacial zones.

The aim is the reconstruction of the October 2019 flash flood, that was documented through extensive field work: rainfall (300 mm in just a few hours), flood marks, times of flood passage and witnesses' snapshots and reports, channel changes, log drift (20,000 trees) and woody debris at bridges, as well as large damage and six fatalities. The methods are: hydrological model built for the rainfall-runoff in the basin and the flood routing in the river, use of hydraulic principles such as flow at waterfalls, flow against obstacles (trees), etc. and finally 1D/2D free surface numerical models. The uppermost 100 km2 produced discharges of 700 m3/s (up to 50 m3/s/km2, locally). Three bridges failed, but their cascading failure (when one failure triggers the next one downstream) was not proved. The main channel widened more than 10 times, dragging away soil and vegetation like a bulldozer. The resulting large wood debris that clogged two bridges worsened the inundation. An anomalous flow downstream, probably a surge of around 1090 m3/s, due to the failure of a woody jam at a narrow bridge, took two lives. Water Authority is now warning flood planners that vegetated, torrential basins may cause catastrophic floods in the valley towns, if their narrow bridges are sensitive to woody debris. Catalan Water Authority and its Tarragona officers, Meteoprades and Fons Signatus, Joan March and a number of witnesses. The UPC's contribution was funded by the contract CTN2000029 of the “Agència Catalana de l′Aigua”. The UB's contribution has been developed within the framework of the AGORA project, funded by the "Agència Catalana de l′Aigua". Our thanks to the "Museu de la Vida Rural", in l′Espluga de Francolí, and all the citizens who contributed to the return of experience. The UIB's research has been supported by the Ministerio de Ciencia, Innovación y Universidades (CGL2017-82868-R and PID2020-113036RB-I00/AEI/10.13039/501100011033 research projects, which are partially supported by the European Regional Development Funds).

By the 1930’s vast areas of the western US were severely degraded by overgrazing and erosion. In response, Congress authorized conservation work including the construction of erosion control and water storage, distribution, and conveyance structures. Thousands of structures such as check dams, water spreaders, and contour berms were built during the 1930s and 40s to control water and sediment in an attempt to restore degraded rangelands. However, across most of the western US, these soil and water conservation measures were implemented without the benefit of local hydrologic data or technical design guidance. Many of the established conservation practices had been developed for humid regions and were untested for use in semiarid areas that are characterized by highly variable rainfall and flash floods. As a result, many structures proved ineffective and were subsequently abandoned. Even in cases where structures were effective, many never received maintenance after their initial construction. Although structurally compromised, abandoned and unmaintained structures continue to alter surface runoff patterns and can greatly exacerbate erosion. Four sites in Arizona, USA were selected to characterize the multi-decadal impacts of conservation structures. Breaches have formed in 100% of contour berms (n = 67) while 96% of water spreader berms (n = 26) were compromised. Localized failures in these structures has created concentrated flow paths that reorganized routing of runoff and sediment thus transforming sheetflow regimes to concentrated flow regimes. This study emphasizes the unintended legacy impacts of soil and water conservation structures and highlights their role as a potential constraint on contemporary resource management.

This study investigates the impact of the October 2016 flash floods in urban areas located in selected catchments along the Nile Valley and Red Sea regions for the assessment and the proposal of feasible mitigation measures. Optical and radar satellite images acquired before and shortly after flash flood events were analyzed to detect and map the active contributing channels, the interfering urban areas, the response of natural depressions and storage areas, and the conveying channels to the flash floods. The quantitative estimates of October 2016 flash floods parameters including total rainfall depths, the active channel cross-sectional areas, and the spatial extent of storage areas of the accumulated flood water were measured. Various hydrological parameters were extracted using the Digital Elevation Model (DEM) for the estimation of water volumes of largely inundated depressions. It was determined that the October 2016 flash floods were devastating in the Ras Gharib area; however, these floods were properly managed at both the New El Minya and New Qena urban areas. In contrast, the flash floods at the Al-Saaf and Atfih urban area require urgent mitigation measures given that wastewater depressions and sanitary facilities are prevalent in the downstream reaches of the studied drainage basins.

Predicting the occurrence and spatial patterns of rainfall induced flash floods is still a challenge. Instant genesis and typically smaller areal coverage of the flash floods are the major impediments to their forecasting. Analysis of the morphometric parameters provides useful insight on hydrological response of the drainage basins to high intensity rainfall events. This information is valuable for understanding the flash flood potential of the drainage basins and for evading the destructions caused by the hazard. Here, we use eighteen morphometric parameters that influence the runoff volume, flow velocity, and inundation depth scenario of a flash flood. The analysis has been carried out for simulating the relative flash flood susceptibility of thirteen watersheds (B1 to B13) of variable sizes in southeastern Bangladesh. The morphometric parameters were derived from Digital Elevation Model (DEM) using Geographic Information System (GIS). The evaluated basin parameters include: area (A), perimeter (P), length (Lb), stream order (Su), stream number (Nu), stream length (Lu), stream frequency (Fs), drainage density (Dd), texture ratio (Rt), bifurcation ratio (Rb), basin relief (Hr), relief ratio (Rr), ruggedness number (Rn), time of concentration (Tc), infiltration number (If), and form factor (F). Two relative flash flood susceptibility scenarios were generated: (i) general watershed level, and (ii) more precise pixel level status. The watershed level comparison reveals that B4 and B6 watersheds constituting 72.61% of the total area are ‘very high’ susceptible, whereas the susceptibility of the other watersheds has been found as ‘high’ [B5 (6.95%)], ‘moderate’ [B8 and B13 (8.63%)], ‘low’ [B2, B10, B11 (4.64%)], and ‘very low’ [B1, B3, B7, B9, and B12 (7.18%)]. The derived watershed susceptibility map was subsequently integrated with two spatial analysis algorithms i.e., topographic wetness index (TWI) and topographic position index (TPI) through overlay analysis. The integration helped to understand the combined role of the general watershed morphometry and the in situ topography for determining the flash flood susceptibility of each spot (30 m × 30 m) within all the selected watersheds. The quantitative analysis and characterization of the watersheds from the perspective of flash flood hazard in this investigation is expected to be useful for implementing the site-specific mitigation measures and alleviating the effects of the hydrological hazard in the study area.

Each year, flash floods in India have affected life, infrastructure and the economy of the country and there is a need for a systemic model of real-time flash flood management. So, to mitigate these losses, we proposed a flash flood management model focused on reinforcement learning. Based on their severity, the flash flood data is collected and rewards are distributed and this data is compared to the data collected from smart IoT devices deployed in the region impacted by the flood. We allocate the state-based reward values once the comparison is completed. The evacuation of flash flood water through the contour of the flash flood is carried out. This bypass has gates at different points that mean that, depending on the incentives, the gates are opened to remove flash flood water. The proposed solution was evaluated to be a faster, more effective and more accurate real-time flash flood management method.

A Large-Eddy Simulation (LES) model is used to study flow dynamics of a flash flood event in a dry-bed, desert wash, the so-called Tex Wash, near the Tex Wash Bridge on Interstate 10 in the Mojave Desert of California. The evolving free surface of the flash flood is tracked using the level-set method. A bed morphodynamics module is coupled to the hydrodynamics model to calculate the erosion and bed evolution of the mobile bed of the wash under flash flood conditions. Flash floods in a desert wash can be characterized with a number of salient features such as the (1) existence of both the dry- and wet-cells on the bed surface of the wash that correspond to the air and water phases, respectively; (2) presence of various flow regimes, critical, sub-critical, and super-critical in the flow domain; and (3) occurrence of a highly transient and complicated flow field and, subsequently, sediment dynamics throughout the wash. A numerical modeling effort is presented to study a recorded flash flood and the corresponding scour processes in the Tex Wash. The flood event occurred in 2015 and lead to the collapse of the Tex Wash Bridge. The of the current study is to gain insight into the flood flow and sediment transport mechanisms, which resulted in the collapse of the bridge. To that end, a study area, which includes a 0.65 km -long reach of Tex Wash at its intersection with the Tex-Wash Bridge, was selected. The bathymetry of the wash was obtained using light-detection-and-ranging (LiDAR) technology and used to construct the computational domain of the wash and bridge foundations. The transient flow of the flash flood, in both air and water phases, and the evolving morphology of the wash are numerically simulated. The site-specific numerical simulation revealed the formation of deep scour regions adjacent to the right abutment of the upstream bridge, where significant erosion caused the collapse of the bridge. Moreover, the results show that most of the scour processes take place during the steady phase of the flash flood when the desert stream is filled with water. However, the transient phase of the flash flood is rather short and contributes to a very limited amount of erosion within the stream.

Satellite precipitation products are very useful as proxies for gauged observations, especially in Africa, where there are sparse in-situ precipitation-measuring weather stations. The two most commonly used satellite precipitation products in Africa (Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) and Tropical Applications of Meteorology Using Satellite and Ground-based Observations (TAMSAT)) and the relatively new Integrated Multi-Satellite Retrievals for GPM early run (IMERG-ER) of the Global Precipitation Measurement Mission (GPM) with soil moisture (GPM+SM2RAIN) are evaluated in comparison to the in-situ observations from the Trans-African Hydro-Meteorological Observatory (TAHMO) project on daily, monthly and annual scales in West (Ghana) and East (Uganda) Africa. Statistical verification methods such as continuous and categorical methods were examined. For both countries, the results showed that all the products showed weak performance in capturing daily precipitation. For the monthly and seasonal scales, all the satellite product performances were very good. Also, small precipitation thresholds (2–5 mm/day) were relatively better detected by all the satellite products. All the products failed to detect intermediate (10–20 mm/day) and large threshold precipitation (>30 mm/day). When the products were examined for disaster management applications over a select number of stations in Ghana and Uganda, the results showed inconsistent and poor performances. Using all the metrics, both CHIRPS and TAMSAT showed similar performances, confirming that their common underlying algorithms are bias-adjusted, whereas GPM+SM2RAIN was different because of its independence from in-situ observations. All the products performed better in Ghana compared to Uganda, which may be due to the latter’s complex terrain. It is possible that CHIRPS and TAMSAT may be better suited for hydrological applications like seasonal forecasting, irrigation scheduling, reservoir operations than for daily or sub-daily processes like flash floods. While all these satellite products have their strengths and weaknesses for various environmental applications in Africa, there is a need for a central platform in Africa for a better or improved precipitation analysis based on the assimilation of climate forecasts, in-situ observations, radar, and satellite observations. This will provide higher temporal (3 hr–6 hr) and spatial (~2 km) resolutions. This study is applicable for scientists, water managers, and decision-makers involved in disaster risk management studies in Africa.

Urban flooding in Chittagong City usually occurs during the monsoon season and a rainwater harvesting (RWH) system can be used as a remedial measure. This study examines the feasibility of rain barrel RWH system at a distributed scale within an urbanized area located in the northwestern part of Chittagong City that experiences flash flooding on a regular basis. For flood modeling, the storm water management model (SWMM) was employed with rain barrel low-impact development (LID) as a flood reduction measure. The Hydrologic Engineering Center's River Analysis System (HEC-RAS) inundation model was coupled with SWMM to observe the detailed and spatial extent of flood reduction. Compared to SWMM simulated floods, the simulated inundation depth using remote sensing data and the HEC-RAS showed a reasonable match, i.e., the correlation coefficients were found to be 0.70 and 0.98, respectively. Finally, using LID, i.e., RWH, a reduction of 28.66% could be achieved for reducing flood extent. Moreover, the study showed that 10%–60% imperviousness of the subcatchment area can yield a monthly RWH potential of 0.04–0.45 m3 from a square meter of rooftop area. The model can be used for necessary decision making for flood reduction and to establish a distributed RWH system in the study area.

This paper presents a review of the variation in the hydro-environment over the past four decades in Wuhan, China, and discusses its close relationship with flash flood events. These flash flood events have inundated underground infrastructures and resulted in significant economic losses and casualties, which are also discussed in relation to various external and internal factors. The external factors are predominantly owing to heavy rainstorms resulting from extreme climate change. The internal factors predominantly include a decrease in wetland areas, changes in topography, and disrepair of drainage systems in urban areas. Since the 1970s, lakes in Wuhan have been significantly reduced in size (by approximately 40%). This reduction in wetland area decreases the water storage capacity in urban areas, and the frequency of large flooding events thus increased from 0.1 event/year to approximately 0.2 event/year. Additionally, the disrepair of drainage systems in urban areas has reduced their ability to resist flood hazards. Changes in topography have also intensified the flood volume per unit time, further burdening the drainage systems. In 2016, Wuhan suffered from several large flooding events that led to some of the most severe economic losses in recorded history. The drainage system at the urban center of Wuhan and proposed flood prevention methods are discussed in detail in this paper. The sponge city (SPC) concept has been attempted in Qingshan District, Wuhan, and its success proved the reliability of the theory. A SPC is believed to reduce the impacts of future flash floods in China and other developed and developing countries. Keywords: Flash flooding, Wetland area, Drainage system, Wuhan, Sponge city

The flash flood that occurred at the end of July and beginning of August 1714 on the Sazava River in the Bohemian-Moravian Highlands (550–750 m above sea level) is probably the most important case of flooding in the Czech lands. The extremity of the flood is likely to be ranked among the most notable occurrences of extreme weather in history, even within the larger Central European context. In this study we have focused on the upper and middle parts of the Sazava catchment (approximately 2000 km2). The aim of our study was to check of the reliability of the flood data in 1714. The main question was whether we should confirm or reject the possible dominant role played by local fishponds, especially the large Dařko fishpond. The extraordinarily high water levels documented by the chronicles were viewed a bit suspiciously at first. The hydraulic evaluation of the flood peak discharges and a reconstructed hydrograph, together with an envelope curve of maximum floods, have confirmed the reliability of the data recorded during the 1714 flood. The contribution of the collapsed fishponds was evaluated as a minor source of flooding. Therefore, the hydrological modelling enabled an estimation of causative precipitation equal to approximately 100 mm/3–4 h as the main flood source. The estimated rainfall amount and peak discharge of 700–1000 m3/s in the catchment area of 1000 km2 are likely to be the main results of the study. We also present an overview of flash floods in Central Europe in 1714, a definition of the affected area on 31 July, the damage, fatalities and a possible scenario of the storm's track. Our results indicate that the 1714 flood represented a unique extreme in Czech territory. The only comparable event appears to be the 25 May 1872 flood at the Berounka and Blsanka catchment.

Flash floods are the highest sediment transporting agent, but are inaccessible for in-situ sampling and have rarely been analyzed by remote sensing technology. Laboratory and field experiments were done to develop linear spectral unmixing (LSU) remote sensing model and evaluate its performance in simulating the suspended sediment concentration (SSC) in flash floods. The models were developed from continuous monitoring in the laboratory and the onsite spectral signature of river bed sediment deposits and flash floods in the Tekeze River and in its tributary, the Tsirare River. The Pearson correlation coefficient was used to determine the variability of correlations between reflectance and SSCs. The coefficient of determination (R2) and root mean square of error (RMSE) were used to evaluate the performance of the generated models. The results found that the Pearson correlation coefficient between SSCs and reflectance varied based on the level of the SSCs, geological colors, and grain sizes. The performance of the LSU model and empirical remote sensing approaches were computed to be R2 = 0.92, and RMSE = ±0.76 g/l in the Tsirare River and R2 = 0.91, and RMSE = ±0.73 g/l in the Tekeze River and R2 = 0.81, RMSE = ±2.65 g/l in the Tsirare river and R2 = 0.76, RMSE = ±10.87 g/l in the Tekeze River, respectively. Hence, the LSU approach of remote sensing was found to be relatively accurate in monitoring and modeling the variability of SSCs that could be applied to the upper Tekeze River basin.

Jeddah is the most important port city in the Kingdom of Saudi Arabia. The climate of Jeddah is mostly dry; however, events of intensive rainfall followed by urban flooding have been reported in recent history. These floods interrupt the logistics and lifelines of the city. In this study runoff analysis and Flash Flood management by the green roof low impact development (LID) control system, has been performed using United States environmental protection agency (EPA)’s Stormwater Management Model (SWMM). Six middle districts of the Jeddah city had been selected and modeled in five sub-catchment areas. The local soil and geographic conditions were incorporated into the model. The effect of the soil-based, rooftop, LID system has been emphasized in the analysis. In flood simulations, 30-70% of the impervious area of each sub-catchment, has been treated with LID. It has been observed that the LID application can significantly reduce the overall flood flow. Thus, simple but well-planned LID control systems can be effectively utilized, for the flood management of heavily urbanized regions.

In 2010, flash floods triggered by Hurricane Alex caused fifteen fatalities in the Monterrey Metropolitan Area (MMA). In contrast, an estimated 225 people died in the 1988 Hurricane Gilbert disaster and reputedly, over 5,000 in the historical flood of 1909. The magnitude of hurricane-related impacts thus appears to be decreasing, indicating higher resilience to this hazard. This paper analyses the process of building resilience to flash floods in the MMA over the last several decades. Knowledge co-production plays a significant role in that process, particularly through the Nuevo Leon State Reconstruction Council, the multi-institutional, public-private-civil group of stakeholders established to guide and coordinate reconstruction efforts following the Hurricane Alex disaster. Findings reveal a complex, protracted and incremental resilience building process, conditioned by the nature of the hazard (infrequent but liable to cause significant damages) and contingent upon the city’s socioeconomic and institutional local context. This local context is embedded in a highly fragmented national water governance architecture that lacks inter-institutional co-ordination and has limited the city’s adaptive responses. Despite definite gains in building resilience, the city faces challenges notably in terms of the conservation and continuing development of knowledge co-produced in the aftermath of disasters.

Despite massive flood protection efforts in China, undertaken since the ancient times, disastrous floods continue to plague the country. In this paper, we discuss changes in flood hazard and flood risk in China. First, we review published results (including our own works) on change detection in observed records of intense precipitation, high river flow and flood damage in China. We provide information on essential features of extreme floods in last decades – floods on large rivers, urban floods, and flash floods. Next, we review available projections for the future (including our own results), related to intense precipitation, high river flow and flood damage in China. We try to interpret the difference in flood hazard projections obtained in various publications. Since the spread of river flood hazard projections is large, projections have to be interpreted with caution, because of the impact on decisions related to climate change adaptation, flood risk reduction, and water resources management. We review flood risk reduction strategies in China, focusing on the present situation and division of responsibilities. China has embarked upon an ambitious and vigorous task to improve flood preparedness, by both structural (“hard”) defences, such as: dikes, dams and flood control reservoirs, and diversions, as well as non-structural (“soft”) measures: spatial planning and zoning; watershed management (source control), flood forecasting and warning systems; and awareness raising. The strategy of flood mitigation includes flood retention and urban water management to alleviate the burden of flash and urban flooding.

The main objective of this research work was to propose and verify a new soft computing approach based on Multivariate Adaptive Regression Splines (MARS) and Particle Swarm Optimization (PSO) for spatial prediction of flash flood susceptible areas. A high frequency tropical typhoon area located on Northwest of Vietnam was selected as a case study. For this purpose, a GIS database for the study areas was prepared, including 654 flash-flood inundations and 12 influencing variables (elevation, slope, curvature, toposhade, aspect, topographic wetness index, stream power index, stream density, Normalized Difference Vegetation Index, soil type, lithology, and rainfall), which were compiled from various sources. The database was used to build and verify the prediction model. We assessed the model’s performance through various indices including Classification Accuracy Rate, Area under the Curve (AUC), Precision, and Recall. We also compared the model’s usability with five state-of-the-art machine learning techniques including the Backpropagation Neural Network, Support Vector Machine, and Classification Tree. The results revealed that the hybrid PSO-MARS model outperformed other benchmark models in all the employed statistical measures. We conclude that the proposed model can be particularly suited for flash flood forecasting problems at high frequency tropical typhoon area.

Irrespective of the magnitude and spatial extend, the consequences of a natural hazard are strongly connected to the vulnerability of elements at risk (e.g. people, buildings and infrastructure). It is, therefore, obvious that an analysis and quantification of vulnerability is required for successful disaster risk reduction. The need for vulnerability assessment is crucial due to the effects of climate change as well as the socio-economic dynamics that may directly impact vulnerabilities and coping capacities of affected communities. Vulnerability is multidimensional (physical, social, economic, etc.), however, the dimension which is mainly related to the direct costs and threat to human lives is the physical one. We focus here on the physical vulnerability of buildings subject to torrential hazards occurring in small and steep mountain catchments. These processes include fluvial sediment transport, debris floods, and debris flows. Furthermore, we included flash flood hazards if these are related to torrential catchments. Physical vulnerability to torrential hazards in mountain areas is a topic that has been under scientific investigation over the last 20 years. Several methods to assess physical vulnerability of buildings towards flash floods, debris flows and hyper-concentrated flows can be found in the literature. The plethora of methods and approaches may be classified under the following three categories: vulnerability matrices, vulnerability curves and vulnerability indices. We provide a short review of these methods which became available over the last decade and which dominate the scientific debate in mountain hazard risk management, giving an emphasis to vulnerability curves. The approaches presented herein are highlighted through case studies from the European Alps and beyond. Furthermore, challenges in vulnerability assessment including data requirements, need for improved event documentation, uncertainties and challenges related to future climate and socio-economic changes are outlined. Finally, a discussion on progress-driving factors such as new technologies (e.g. mobile apps, drones), citizen science and new innovative assessment methods is provided.

Flash flood is a typical natural hazard that occurs within a short time with high flow velocities and is difficult to predict. In this study, we propose and validate a new soft computing approach that is an integration of an Extreme Learning Machine (ELM) and a Particle Swarm Optimization (PSO), named as PSO-ELM, for the spatial prediction of flash floods. The ELM is used to generate the initial flood model, whereas the PSO was employed to optimize the model. A high frequency tropical typhoon area at Northwest of Vietnam was selected as a case study. In this regard, a geospatial database for the study area was constructed with 654 flash flood locations and 12 influencing factors (elevation, slope, aspect, curvature, toposhade, topographic wetness index, stream power index, stream density, NDVI, soil type, lithology, and rainfall). The model performance was validated using several evaluators such as kappa statistics, root-mean-square error (RMSE), mean absolute error (MAE), coefficient of determination (R2), and area under the ROC curve (AUC-ROC) and compared to three state-of-the-art machine learning techniques, including multilayer perceptron neural networks, support vector machine, and C4.5 decision tree. The results revealed that the PSO-ELM model has high prediction performance (kappa statistics = 0.801, RMSE = 0.281; MAE = 0.079, R2 = 0.829, AUC-ROC = 0.954) and successfully outperformed the three machine learning models. We conclude that the proposed model is a new tool for the prediction of flash flood susceptibility at high frequency tropical typhoon areas.

Increasing incidences of flash floods highlight the need for a reliable flood forecasting system to minimize the losses of lives and property. The most formidable challenge of flood forecasting is the availability of high resolution and accurate precipitation forecast despite having a sophisticated 3-ways flood hydrodynamic model. Global rainfall forecasting products are of coarse resolution, which makes them less reliable for urban flood forecasting. Therefore, high-resolution regional weather forecasting models such as the Weather Research and Forecasting (WRF) model are used to generate fine-scale rainfall estimates. Precipitation forecasting from the WRF model is highly dependent on model configuration, especially cumulus (CU) parameterization and microphysics (MP) schemes. In the present study, three physics schemes that include two urban, four CU and three MP schemes of WRF model are investigated for extreme precipitation estimates. The six events comprised of two of the highest rainfall events of the years 2012, 2013 and 2014 have been selected for investigation over Mumbai, India. The events are simulated using initial and boundary conditions from the ERA-Interim Reanalysis dataset. The simulated rainfall events are evaluated against the observations from 28 automatic weather stations over Mumbai. The analysis suggests that building environment parameterization (BEP) scheme influences the spatial pattern of the rainfall along with the reduction in rainfall bias. Further, CU schemes affect the magnitude of the rainfall while MP schemes have a lesser impact than the former. WRF simulations with BEP urban scheme, Grell-Devenyi 3D CU, and Lin MP scheme performs best (out of selected combinations). Besides, the best performing scheme has been tested with initial and boundary conditions from the global forecasting system (GFS) for the same events; the results have shown improved rainfall estimates than the GFS forecasts.

This study analyses the downstream hydrological, morphological, and socio-economic impacts of the sole operating hydropower scheme - Ranganadi Hydel Project Stage I in Arunachal Pradesh (India), the state with the largest potential and the highest number of upcoming hydro schemes in the country. The project has a large dam with inter-basin water diversion for electricity generation, thereby affecting flow in two rivers of the Brahmaputra Basin - Ranganadi and Dikrong. Flow alterations were measured using Nature Conservancy's Indicators of Hydrological Alteration model, while planform changes were studied using multi-temporal satellite imagery and Geographical Information System. The results indicated significant downstream flow alterations by the project in the post-dam period. Post-dam median annual flows in the impounded and flow-deprived river - Ranganadi, have decreased by 63%, but increased by 138% in the recipient river - Dikrong. The former displayed channel narrowing and decreased braiding, while the latter exhibited a wider and more braided planform. Unexpected releases from the reservoir, flash floods, and sand casting were the major problems cited by the downstream communities in the Ranganadi sub-basin, which impacted upon agricultural lands and livelihoods. This study recommends mitigation plans that could be followed by both existing and future hydropower projects.

Flash floods are among the most devastating natural hazards but the analyses of flash floods are hindered by the lack of hydro-meteorological data. In particular, data issues are critical in ungauged basins. This paper presents an investigation of flash flood modeling using coupled hydrological and hydrodynamic models. Specifically, the TOPography-based hydrological MODEL (TOPMODEL) is employed to obtain the flood hydrograph and the coupled 1D-2D hydrodynamic model MIKEFLOOD is used to simulate floodplain inundation. The methods are tested in the Pajiang River, a mountainous basin in South China. The results show that the TOPMODEL effectively simulates the flood hydrograph and the Nash–Sutcliffe coefficients of the flow rate are larger than 0.80 for both calibration and validation. Also, MIKEFLOOD effectively simulates the flood inundation extent and flooding depth and the BIAS for simulated water level is −0.004 m. Further, using socioeconomic and historical flood disaster datasets, areas with high flash flood risk are identified. A flash flood risk assessment shows a clear trend of change in the flood hazard and the spatial heterogeneity of the flood vulnerability is significant. A sensitivity analysis of the flood vulnerability to the socioeconomic indicators indicates that cultivated land is the most sensitive indicators, and the population and the construction areas have similar influences. Overall, the coupled hydrological and hydrodynamic models prove effective and can be used in practical applications for flash flood risk mapping.

The anticipation of flash flood events is crucial to issue warnings to mitigate their impact. This work presents a comparison of two early warning systems for real-time flash flood hazard forecasting at regional scale. The two systems are based in a gridded drainage network and they use weather radar precipitation inputs to assess the hazard level in different points of the study area, considering the return period (in years) as the indicator of the flash flood hazard. The essential difference between the systems is that one is a rainfall-based system (ERICHA), using the upstream basin-aggregated rainfall as the variable to determine the hazard level, while the other (Flood-PROOFS) is a system based on a distributed rainfall-runoff model to compute the streamflows at pixel scale. The comparison has been done for three rainfall events in the autumn of 2014 that resulted in severe flooding in the Liguria region (Northwest of Italy). The results obtained by the two systems show many similarities, particularly for larger catchments and for large return periods (extreme floods)., 34 pages, 1 Table, 15 Figures

Attica, which is the region with the largest population in Greece, suffers from numerous high rainfall intensity events inducing flash floods and, consequently, significant damages in the urbanized areas. High rainfall intensities are frequently connected with convection, a quiet often phenomenon during either the transitional seasons or the late summer thunderstorms. The objective of this paper is to implement and evaluate a stratiform-convective classification technique for the rainfall events occurred in Attica during the period 2005–2016. As this methodology requires only the precipitation records, the satisfactory evaluation of this classification approach allows further applications, such as, a climatological analysis regarding convective and stratiform trends in the study area and generally in Greece. Particularly, the rain gauge stations' records used correspond to 10-minute time series from 32 rainfall stations for the same period, and these data are analyzed and processed in order to fit a suitable exponential curve describing the stratiform component. A critical annual threshold of rainfall intensity in mm/6h is then calculated, separating the prevailing convective and stratiform regime above and below this value, respectively. The analysis is performed in three individual subareas of Attica region demarcated initially according to their morphological characteristics and subsequently by checking the cross-correlation for each pair of stations. This critical intensity threshold is determined for each year separately, in order to illustrate the uncertainty and the difficulty in identifying a standard threshold, as it is related to the annual behavior of precipitation. Using this threshold, a total of about 180 six-hour case events is detected as purely convective cases, however this number ranges for each subarea. For these cases, a further analysis is performed with the aim of verifying their convective character. Verification includes time-accurate lightning data, surface synoptic observations from the Hellenic National Meteorological Service and six-hour surface analysis charts from UK MetOffice. Findings, which are presented via indicative verification indices, show in general encouraging performance, considering the highly variable nature of convective precipitation which poses considerable problems in its identification with quite simple techniques.

The need to attenuate hydrograph peaks is central to the design of stormwater and flood control systems. However, few guidelines exist for siting hydraulic control structures such that system-scale benefits are maximized. This study presents a new graph-theoretic algorithm for stabilizing the hydrologic response of watersheds by placing controllers at strategic locations in the drainage network. This algorithm identifies subcatchments that dominate the peak of the hydrograph, and then finds the “cuts” in the drainage network that maximally isolate these subcatchments, thereby flattening the hydrologic response. Evaluating the performance of the algorithm through an ensemble of hydrodynamic simulations, we find that our controller placement algorithm produces consistently flatter discharges than randomized controller configurations—both in terms of the peak discharge and the overall variance of the hydrograph. By attenuating flashy flows, our algorithm provides a powerful methodology for mitigating flash floods, reducing erosion, and protecting aquatic ecosystems. More broadly, we show that controller placement exerts an important influence on the hydrologic response and demonstrate that analysis of drainage network structure can inform more effective stormwater control policies.

An accurate assessment of Flash-Flood Potential for certain areas is mandatory for the improvement of flash-flood forecast and warnings. The main aim of the present study is represented by the calculation of Flash-Flood Potential Index within the upper and the middle sector of Prahova river catchment (Romania) by using 4 hybrid models: Logistic Regression-Frequency Ratio (LR-FR) model, Logistic Regression-Weights of Evidence (LR-WoE) model, Support Vector Machine-Frequency Ratio (SVM-FR) model and Support Vector Machine-Weights of Evidence (SVM-WoE). The identification of areas affected by torrential phenomena represents the first step performed in the present research. These areas with a total surface of 260 km2 were divided into training areas (70%) and validating areas (30%). By the mean of Linear Support Vector Machine (LSVM) model, 10 flash-flood conditioning factors were selected and further used for the Flash-Flood Potential assessment. Based on the spatial relationship between areas affected by torrential phenomena and flash-floods conditioning factors characteristics, the FR and WoE coefficients were calculated. In order to be integrated into Logistic Regression and Support Vector Machine (RBF) analysis, these values were standardized. According to the results of the 4 hybrid models used for FFPI calculation, the high and very high Flash-Flood Potential are spread over 33% of the study area. The model performance assessment and results validation were carried out by the mean of the three different methods: i) relative frequency distribution of torrential phenomena pixels within FFPI classes; ii) ROC Curve (Success Rate and Prediction Rate) and AUC value; iii) statistical measures represented by Sensitivity, Specificity and Accuracy.

The coastal and alluvial areas of the Red Sea Mountains are mainly being developed for resorts and tourism activities. Given the development of occasional flash floods in the central part of the Red Sea area can be of destructive consequences to the various anthropogenic activities; thus the quantitative and qualitative assessments of the hydrological parameters and groundwater occurrence are presented. As a case study, Wadi Isl at the Red Sea coast has been hydrogeologically analyzed using an integrative approach of remote sensing , GIS and direct current resistivity (DCR) tools. The time area-zones have been estimated using and Manning's equation into the spatial analyses routines embedded within the ArcGIS. In this study, a synthetic effective rainfall of 10 mm has been applied to compute the spatially distributed runoff hydrograph . The estimated total runoff volume is approximately 8 million cubic meters, and the peak discharge rate is estimated to 163 cubic meters per second, which can be destructive to the main infrastructures in the flash flood pathways. Then, the 2D-electrical resistivity tomography (2D-ERT) surveys have been carried out at various localities along the main wadi course to explore the lateral and vertical variation of alluvium thickness and the saturated zones . Notably, the groundwater occurrence is contained in the structurally controlled graben . Therefore, the study has recommended the construction a main barrier at a natural deep gorge of the main outlet in order to fully control the flash floods and to enhance the potential recharge to the underlying alluvium aquifer. The present integrative approach of both surface and subsurface data is definitely needed to maximize the flash flood benefits.

Flash floods cause severe natural disasters over the world generating property and infrastructures damages, poverty and loss of human life, among others. Mediterranean coastal watersheds are specially sensible to flash floods effects due to their typical drainage basin features (steep slopes, short concentration times, complex orography, etc.) and the high rainfall intensity typical of convective systems. In the present study, the temporal evolution of the hydrological answer in five Mediterranean (SE Spain) ravine basins with sizes from 10.2 km2 to 200.9 km2 were analysed. A sub-daily SWAT model was used at watershed scale to capture the complex hydrological dynamics. Five land use scenarios corresponding to no-urbanization (baseline), 1990, 2000, 2006 and 2012 were evaluated using GIS-based tools. Additionally, statistical significant differences among the studied scenarios were checked employing the Kruskal-Wallis and post-hoc tests based on Mann-Whitney test with BH correction. Our results show that flash flood risks have increased in the studied catchments due to changes in land uses, particularly affected by a large urban growth. Observed changes in soil uses have been important since the sixties of the last century, because of a high demographic and touristic pressure and specially the urban area has enhanced considerably during the last 22 years. Currently, some of these catchments present around 70% of their surface occupied by urban land uses with high population density producing curve number surpasses 85 and 90 levels. The hydrological response of the studied basins changed to higher flow rate peaks and shorter concentration times. Some discharges increased significantly from the baseline land use scenario (≈50 m3/s, 190 m3/s, 380 m3/s) to the most urbanised scenario (≈235 m3/s, 385 m3/s, 940 m3/s), respectively. These findings provide to urban planning policy makers very useful information in the face of flash flood effects, which have cost even human lifes in the studied ravine basins during last years. Financial support was provided partially by the University of Alicante, project GRE17-12. This study also has been conducted within the grant received from the Programa Nacional de Formación de Profesorado Universitario (FPU) conceded by the Spanish Ministry of Science to the first author.

The 2013 Uttarakhand flash flood was such a surprise for those at risk that the predominant source of information for their risk was environmental cues and, secondarily, peer warnings rather than official warnings. Of those who received warnings, few received information other than the identity of the flood threat. A survey of 316 survivors found that most people's first response was to immediately evacuate but some stayed to receive additional information, confirm their warnings, or engage in evacuation preparations. Unfortunately, engaging in these milling behaviors necessarily delayed their final evacuations. Mediation analysis revealed that psychological reactions mediated the relationship between information sources and behavioral responses. Further analyses revealed that immediate evacuation and evacuation delay were both predicted best by information search and positive affect, but correlation analyses indicated that a number of other models were also plausible. Final evacuation was best predicted by immediate evacuation and, to a significantly lesser extent, household together. Overall, results suggest that the Protective Action Decision Model (PADM) should be considered a useful framework for examining household responses to flash floods in developing countries like India. It supports the conclusion that a household's first warning source is a function of two distinct detection and dissemination systems within a community—an official system and an informal system. However, it fails to capture what pre-impact emergency preparedness entails for rapid onset events in a developing country context. Further research is needed to determine the relative importance of situational and cultural characteristics in producing these observed differences.

Single-mission altimetric water level observations of rivers are spatially and temporally limited, and thus they are often unable to quantify the full extent of extreme flood events. Moreover, only missions with a short-repeat orbit, such as Envisat, Jason-2, or SARAL, could provide meaningful time series of water level variations directly. However, long or non-repeat orbit missions such as CryoSat-2 have a very dense spatial resolution under the trade-off of a repeat time insufficient for time series extraction. Combining data from multiple altimeter missions into a multi-mission product allows for increasing the spatial and temporal resolution of the data. In this study, we combined water level data from CryoSat-2 with various observations from other altimeter missions in the Mekong River Basin between 2008 and 2016 into one multi-mission water level time series using the approach of universal kriging. In contrast to former multi-mission altimetry methods, this approach allows for the incorporation of CryoSat-2 data as well as data from other long or non-repeat orbit missions, such as Envisat-EM or SARAL-DP. Additionally, for the first time, data from tributaries are incorporated. The multi-mission time series including CryoSat-2 data adequately reflects the general inter-annual flood behaviour and the extreme floodings in 2008 and 2011. It performs better than single-mission time series or multi-mission time series based only on short-repeat orbit data. The Probability of Detection of the floodings with the multi-mission altimetry was around 80\% while Envisat and Jason-2 single-mission altimetry could only detect around 40% of the floodings correctly. However, small flash floods still remain undetectable., published in Journal of Hydrology

The study of precipitation and temperature variability in Portugal, including their extremes, is often restricted by the lack of high-resolution gridded datasets at daily timescales and available for sufficiently long time periods. They are of quite importance specially when considering hydrology modeling at a local scale. To overcome this limitation, we develop new high-resolution gridded datasets (∼1 km) of daily precipitation (1950–2015) over Portugal. Daily precipitation is downscaled by ordinary kriging from a coarser gridded dataset (∼20 km). Daily temperatures were retrieved from a previous work and extracted for the target watershed in this study, Corgo River (northern Portugal). The aim of the present study was to investigate the potential of the new high-resolution data in improving the performance of a distributed hydrologic model, Hydrological Simulation Program – FORTRAN (HSPF) in simulating flowrates at one target watershed in northern Portugal (Corgo River watershed), thus providing a practical basis for subsequent hydrological analysis. The performances of the HSPF model, driven by either a single weather station or the new gridded datasets are compared. The results clearly hint at an improved model performance when using our dataset (Nash-Sutcliffe coefficient of efficiency at daily timescale: 0.34 for the single-station run and 0.64 for the multi-point run). A good performance was also found in reproducing specific flash flood events. Although the advantage of using these novel climatic datasets for hydrologic modeling in Portugal is demonstrated herein, they can be applied to other areas of research, such as ecology, agriculture and forestry, contributing to more accurate decision support systems to assist decision-makers and stakeholders.

Fluvial features such as floodplains and point bars are built by sediment deposition and sculpted by erosion. Long-term measurements (38 yr) of the cross-section topography of active floodplains and point bars along the freely-meandering Powder River in southeastern Montana, USA (mean daily discharge of 12.5 m3 s−1), were used to develop dynamic relations between annual sediment deposition and peak-flood discharge. Five floodplain sections and five point-bar sections were selected from 24 cross sections along a 90-km study reach. At each cross section the sediment deposition volume per unit streamwise distance was computed as the difference between two topographic surveys made in consecutive years. Snowmelt floods were found to be the dominant annual process. However, other processes such as flash floods, ice breakup floods, and autumnal floods were important episodically. The dynamic relations were linear for both fluvial features. The snowmelt deposition-discharge relations showed, in general, that point bars were about two times more efficient at trapping sediment than floodplains. Each relation had a discharge threshold that must be exceeded before sediment was deposited. Although these discharge thresholds for floodplains and point bars had essentially the same mean value (69 and 71 m3 s−1, respectively), they represented different processes. Thresholds for other rivers will probably differ from those for Powder River because of different channel geometry and sediment characteristics.

On November 15, 2017, a high intensity convective storm, reaching 300 mm in 13 h in the core zone of the event, hit the western part of the region of Attica in Greece, causing a catastrophic flash flood in the town of Mandra and a tragic loss of 24 people, making it the most deadly flood in the country, in a period of 40 years. The research team surveyed the area during and after the flood using a combination of systematic ground and aerial observations with the aid of an unmanned aerial vehicle (UAV), aiming to reconstruct the basic physical and hydrological characteristics of the flood and its impacts. The analysis produced detailed flood extent and depth maps that provided a comprehensive description of the physical characteristics of floodwaters across the inundated area. Peak discharge was estimated, using a UAV-derived digital surface model, at two locations, corresponding to the two main tributaries and indicated an impressive hydrological response, between 9 and 10 m3/s/km2. Impact analysis on the basis of these observations showed an extensive diversity, including effects in geomorphology, vegetation, buildings, infrastructure and human population. Analysis of meteorological, botanical and geomorphological evidence lead to the conclusion that this flash flood was a very rare event. Results demonstrate that the combination of aerial and ground observations allow an enhanced and holistic reconstruction of a flash flood and its impacts with high accuracy, leading to the conclusion that the approach used has a significant potential in many aspects of flood disaster investigations.

This study was conducted to evaluate the quality of water in selected dams in Albaha region, Kingdom of Saudi Arabia. Water samples from eight dams were subjected to physical, chemical, and bacteriological assessment using standardized procedures of conductivity, total dissolved solids, ions, acidity & alkalinity, and EC blue 100® coliform detection. About three fourth (75%) of dams’ water samples exceeded the permissible levels of pH, total dissolved solids, turbidity, Mn and NO3 set by Saudi standards. Average levels of total dissolved solids, Fe, Mn, SO4, NO3, and NO2 were 3065.00, 0.10, 0.89, 68.25, 17.91 and 0.016 mg/L, respectively. However, the average pH of water samples was 7.95 ± 0.66 which still within the accepted range set by national and global standards. Moreover, total dissolved solids also exceeded regular standards of Food and Agriculture Organization for irrigation water quality. Coliform bacteria were detected in 37.5% of dams without any significant spatial differences between dams and sites as groups. Correlations were found between pH & NO3, SO4 & NO3, coliform bacteria & turbidity, coliform bacteria & NO2 levels. Increased concentrations of assessed parameters in dams may be attributed to agricultural activities as well as animal and human wastes deposited into dams via rainfalls and flash floods. Proper treatment of dams needs to be taken into account before consumption and irrigation.

The main focus of the present study is to examine the presence of Atmospheric Rivers (ARs) in the occurrence of Chennai (13.5° N, 80.5° E) flood event over Tamil Nadu which is south-eastern part of Indian peninsular region of India during November to December 2015. The vertically integrated horizontal water vapor transport (IVT) algorithm was used for the detection of ARs using three different reanalysis products, namely, the NCEP-NCAR (National Center for Atmospheric Research), NASA's Modern-Era Retrospective Analysis for Research and Applications (MERRA) and ECMWF Interim Re-Analysis (ERA-Interim). It is noticed that the occurrence of heavy precipitation events (HPEs) prior to the flood in the Chennai city, has been in good agreement with the presence of ARs during that time. The distribution from TRMM-3B42RT, TRMM-3B42 are validated with the with in situ rain gauge observations over the Chennai city. We have conducted quantitative analysis of IVT and their impact on heavy precipitation events and flood occurred over Chennai city. It is seen that MERRA reanalysis could be able to provide better presence of ARs. The study mainly reveals that persistent ARs of >18 h resulted in extremely heavy precipitation and lead to associated flood over Chennai. Also, the atmospheric conditions, ARs and rainfall simulated from Advanced Research Weather Research and Forecasting model (ARW) show good agreement with reanalysis and observations. Over the given reference period 1979–2015, correlation between IVT and HPEs is statistically significant at 99.5% confidence level. But the correlation between IVT during persistent ARs and corresponding HPEs is statistically significant at 90% confidence level. A large fraction of HPEs occur after ARs, with a small portion of ARs would lead to HPEs. The Chennai gird historical rainfall data is suitably fitted by Extreme Value Distribution (EVD) models. Inference model using the Maximum Likelihood Estimation (MLE) was applied on EVD considering their impact on the shape parameter and the confidence interval width. A Non-stationary generalized extreme value (GEV) analysis, was used to determine the strength of association between the precipitation extremes and IVT. The influence of the location and the scale parameter in the GEV model on different return levels (2-year, 20-year, and 100-year) are explicitly described. The return-level threshold values are found to change with IVT considerably. This study advocates that the detection of ARs can be used as important proxy in identifying the likelihood of occurrence of heavy precipitation/flash flood events for a given location using reanalysis data sets.

This study examines the variation in the concentration of eight heavy metals (Cu, Ni, Pb, Cd, Cr, Co, V, Sc) bound on suspended sediments during flow events and those deposited in channel banks. The study was undertaken in Wadi Sekher, an ephemeral flash-flood channel draining the Neot Hovav industrial chemical complex in the semi-arid northern Negev, Israel, at sites varying with bank height and distance from the industrial complex. Metal concentrations were found to be higher in the initial flow and recession than during peak flow. Bound metal concentrations were mainly affected by suspended sediment composition and concentrations. During peak flow the suspended sediment concentration rises and quartz sand is a major constituent. This leads to a decrease in bound metal concentrations, as the larger particles have a weaker affinity to binding. In six sediment samples, taken during the first 15 min of two floods, the bound metal concentrations changed similarly. These changes are suggested to represent variations in the source and cannot be attributed to dilution or binding effects. Six banks were sampled along Wadi Sekher, from the Neot Hovav hydrometric reach downstream to the confluence of Wadi Sekher and Wadi Beer-Sheva, at specified heights, following a bank-full flood. In every cross-section, a significant difference (p 0.05) undifferentiated, indicating that the industrial area is not a source point for these metals, and that a constant input exists into the channel from tributaries along the channel. Due to the difficulty in sampling flash floods in ephemeral channels, existing data are not abundant, and our understanding of these environments is therefore limited. This study improves knowledge of interrelated variations in bound metal concentrations in fluvial deposits, in suspended sediment and in water during flash floods.

The mismatch between the space-time scales of flash flood occurrence and those of the typical hydro-meteorological monitoring networks has stimulated the development of forensic flash flood analysis, which involves post-flood indirect peak discharge estimation in ungauged channels and flood response modelling driven by weather-radar rainfall estimates. However, both approaches are potentially affected by significant uncertainties. Assessment of scale dependence of such uncertainties is important to identify how uncertainty affecting forensic flash flood analysis increases with decreasing basin size. In this work, we apply the forensic methodology to the flash flood of November 18, 2013 in Sardinia (Italy). We introduce the 'flash flood forensic consistency index' as a tool to compare the probability distribution of peak discharge uncertainties from observational and model estimates, and to determine the scale effects of the forensic analysis concept. Uncertainties in field-based peak flow estimates are evaluated through a first-order error analysis of the Taylor-series approximation of the slope-conveyance method, whereas uncertainties in flash flood modelling are based on the Generalized Likelihood Uncertainty Estimation methodology using a distributed hydrologic model. Results show no significant relationship between observational and modelling uncertainties, considered independently, and basin area and channel bed slope. Conversely, when considering the interaction between the two uncertainty distributions, a relationship arises between their degree of overlap and basin size. In particular, with decreasing basin area or increasing channel bed slope, the absolute relative bias between the estimated peak flow values increases more than their relative uncertainties, decreasing the consistency index. This calls for more robust approaches for the analysis of flash flood response in small-sized rugged-relief mountain basins, which are of high interest for flood risk management.

Nowadays, rapid growths of urban areas and associated Land Use/Land Cover (LULC) changes notably affect the surface runoff response to rainfall in urbanised catchments. This effect of urbanisation on surface runoff is frequently addressed since it relates to the increasing incidence of pluvial floods worldwide. Studies on this issue commonly assess runoff changes over several most recent decades. However, human-induced factors likely resulted in increased surface runoff and associated flash floods in rural catchments even in the past centuries. Such long-term changes have been rarely studied and thus are not well documented. This paper aims to fill this gap and assess the surface runoff response to LULC changes in a small catchment in southwestern Slovakia over more than two centuries. To meet this goal, we applied the Soil Conservation Service Curve Number (SCS-CN) method. We mapped past (1784) and present (2018) LULC classes based on historical maps and modern remote sensing data. Then, we estimated surface runoff depths for specific design rainstorms for both periods by executing CN method equations in the ArcGIS environment. Results revealed significant changes in surface runoff conditions between evaluated periods. In total, surface runoff magnitudes increased by ~230 and ~ 130% for 40- and 65-mm design rainstorms, respectively, compared to 1784. Moreover, surface runoff values show different spatial patterns on historical and present-day output raster images revealing spatial redistribution of runoff-enhancing and runoff-preventing areas during the evaluated period. Although both infiltration-enhancing and runoff-enhancing effects of LULC changes were identified, the latter effect associated with urbanised lowland areas was recognised as prevailing at present. In contrast, runoff-promoting conditions were associated with hilly vineyard areas in the past. These findings likely have important implications for understanding the past and present LULC-based controls of surface runoff generation and flash floods initiation.

Fugitive dust sources within the Keeler Dunes, a small shoreline dune system in the northeast corner of Owens (dry) Lake in Owens Valley, California, U.S.A. were investigated. PM10 flux potential was quantified using measurements from a Portable In-Situ Wind Erosion Laboratory (PI-SWERL). Stratified random sampling was used to evaluate potential PM10 fluxes from eight landforms, as determined by high-resolution satellite imagery and ground observations, found within the vicinity of the Keeler Dunes. Within each landform, potential PM10 flux for one or more representative surface types was measured. A total of seven surface types were identified, several of which existed on different landforms. The results indicate that the major determinant of potential PM10 flux is the landform type. Furthermore, the highest potential PM10 fluxes are from landforms characterized by surface deposition of alluvial sediment. Within the Keeler Dunes Complex, these landforms are associated with the severely eroded 1944 shoreline coppice dunes, flash flood channels, and flash flood deposits. In the Owens Valley, studies of dust emissions have tended to focus on aeolian landforms. However, similar to measurements of potential PM10 flux from desert landforms across the globe, this investigation points to the importance of alluvial landforms as major sources of dust emissions within the Owens Valley region. This article is a part of a larger investigation into the modern destabilization and migration of the Keeler Dunes (Schaaf et al. this issue).

For accurate flash flood forecasting and effective stormwater planning and management in urban areas, it is necessary to model not only the natural channel systems but also the large and complex networks of storm drains. In this work, we describe a modular storm drain model that can easily be coupled with existing gridded distributed hydrologic models for real-time flash flood forecasting, and stormwater planning and management for large urban areas (>100 km2). A salient feature of our approach is the use of the equivalent storm drain network (ESDN) which approximates the actual network on the same grid as that of the distributed hydrologic model, thereby rendering coupling simple and modular. In the integrated model, storm-drain flow occurs through the simplified network coarsened to the resolution of the distributed hydrologic model without full 1D-2D dynamics or very detailed man-made structures and features modeled. The integrated model is applied to a 144.6 km2 area of five urban catchments in the Cities of Arlington and Grand Prairie in Texas, US. Comparisons at selected locations using kinematic-wave flow simulations show that the ESDN approximates the flow through the original network very well with attendant savings in computational amount and reduction in modeling complexities. The impact of the storm drain network is assessed via a combination of simulation experiments, sensitivity analysis and limited comparison with observed flow. It is shown that the storm drain network in highly urbanized catchments in the study area is very effective in reducing surface flow at most locations for about 30 min following onset of significant rainfall, that the existing stormwater infrastructure would lose effectiveness for approximately 30% of the study area with a 15% increase in imperviousness relative to the current conditions, and that significant uncertainties exist in partitioning of surface flow into storm drain and natural channel flows due to sensitivity to inlet flow modeling. With greatly reduced computing cost and modeling complexity, the proposed approach offers a practical solution for integrated stormwater modeling for large urban areas for a wide range of applications. The proposed approach cannot, however, resolve flow at sub-grid scales and hence is not appropriate for very detailed modeling for small areas.

Impacts of global climate change can be seen worldwide, both on developing and developed economies. In recent years, numerous researches have been carried out by the Government and Non-Government agencies in understanding, assessing, predicting, and responding to expected processes of global climate change and recommend policies for mitigation. Extreme weather events like increased precipitation, cloudbursts, flashfloods, and avalanches in the mountainous region threaten human lives, and state and national economies. In the Indian Himalayan Region (IHR), well distributed hydrometeorological records (contemporary and historical) that facilitate the understanding of processes driving extreme weather events are scarce or rarely available. However, the capacity to observe, measure and quantify precipitation on regional scales has increased tremendously over the last three decades. Topography of the IHR provides favorable conditions for the cloudburst phenomenon which lead to frequent flashfloods and landslides; killing hundreds of people every year. Understanding the exact mechanism of the driving processes of cloudbursts such as orographic lifting, precipitation distribution, precipitation thresholds and its source or origin are still uncertain. Keeping in view that cloudbursts have been increasing in both their frequency and intensity, they are likely to intensify in the near future. Present study analyzes and critically summarizes facts and impacts of cloudburst events through compilation of hydrometeorological records and analysis of available data in the IHR. Results indicate that natural climate variability has played a much greater role in driving these extreme events than earlier thought. A general consensus is observed about the role of climate change, large atmospheric circulations, teleconnections and landuse–landcover changes in driving these events. Therefore, in light of such challenges and potential research gaps, this paper aims at producing actionable knowledge in the IHR for climate modelers and policy planners to better serve the nation's needs.

In the mountainous area of Assiut plateau in southwestern Egypt, a proposed road is designed to pass through a flood path near Durunka village. A reliable and accurate information about natural hazards, could occur in this region especially flash floods, is required. Due to the lack of this information, a runoff model is built adopting the Soil Conservation Service method for an un-gauged watershed of Assiut plateau. The hydrologic characteristics and soil type and cover for the study area are estimated during a site visit. The watershed is delineated and the morphometric parameters are derived from analyzing the SRTM3 Digital Elevation Model (DEM) using Geographic Information System (GIS) to construct a hydrological model. This model provides a good estimate about the magnitude of flash floods including the water velocities and depths using HEC-RAS. Two rainfall events are used in this analysis, the first event is a storm with 50 years return period, and the second event is for highest precipitation value recorded in this area. The model showed that the maximum water depth could occur is 4.01 m and the highest water velocity is 11.75 m/s. The results of this study could help the decision makers in protecting the proposed road and to minimize the flood hazards. Keywords: Hydrology, GIS, Assiut plateau, Flood hazards, Egypt

This work presents a post-event survey study, addressing the geomorphic response and large wood budget of two torrents, Grimmbach and Orlacher Bach, in southwestern Germany that were affected by a flash flood on May 29, 2016. During the event, large amounts of wood clogged and damaged a bridge of a cycling path at the outlet of the Grimmbach, while the town of Braunsbach was devastated by discharge and material transported along the Orlacher Bach. The severity of the event in these two small catchments (30.0 km 2 and 5.95 km 2 , respectively) is remarkable in basins with a relatively low average slope (10.7 and 12.0%, respectively). In order to gain a better understanding of the driving forces during this flood event an integrated approach was applied including (i) an estimate of peak discharges, (ii) an analysis of changes in channel width by comparing available aerial photographs before the flood with a post-flood aerial surveys with an Unmanned Aerial Vehicle and validation with field observations, (iii) a detailed mapping of landslides and analysis of their connectivity with the channel network and finally (iv) an analysis of the amounts of large wood recruited and deposited in the channel. The morphological changes in the channels can be explained by hydraulic parameters, such as stream power and unit stream power, and by morphological parameters such as the valley confinement. This is similar for LW recruitment amounts and volume of exported LW since most of it comes from the erosion of the valley floor. The morphological changes and large wood recruitment and deposit are in the range of studied mountain rivers. Both factors thus need to be considered for mapping and mitigating flash flood hazards also in this kind of low range mountains.

Globally, a number of catastrophic hydrometeorological hazards occurred in 2017 among which the monsoon floods in South Asia was particularly disastrous, killing nearly 1200 people in India, Nepal and Bangladesh. The wetland region (Haor) of northeastern (NE) Bangladesh was severely affected by flash floods early in 2017, affecting nearly 1 million households and damaging US $450 million worth of rice crops. This study investigates how the NE Bangladesh experienced the 2017 flash floods, and to what degree the wetland communities are vulnerable and resilience to flash floods. Focus group discussion, key informant interviews, and household questionnaire surveys (n = 80) were applied in the study area of Sunamganj district. Results from statistical analyses and regression modelling reveal that poor people are particularly vulnerable to floods but they are also more adaptive and thus resilient; middle-income households are vulnerable as they are hesitant to take up any jobs and accept flood relief; and rich households, despite being less adaptive, are able to recover from flood disasters because of wealth. This study reveals that resilience also stems from deep religious faith in the Haor inhabitants that supports communities to move on by accepting that most natural calamities such as flash floods are divine tests. This study also finds that women are particularly vulnerable and less resilient as they are not normally allowed to work outside of their homes and beyond the Haor communities due to cultural and religious reasons.

Economic losses caused by flash floods are expected to rise worldwide in the coming decades, which is largely due to the increasing exposure of elements at risk. Therefore, a comprehensive analysis of the economic context of the potentially affected areas is highly recommendable. Numerous papers have been published to date that focus on quantifying vulnerability in general and in areas affected by floods in particular. However, the number of studies devoted to flash flood-prone areas is far lower. Integrated economic vulnerability assessment enables one to learn what characteristics explain, trigger, intensify, and attenuate the exposure, sensitivity, and resilience of economically vulnerable populations, which can be combined to achieve an Integrated Economic Vulnerability Index (IEVI). The methodology deployed here was conducted in Castilla y Leon (northwest Spain; 94.223 km2) and has allowed the economic vulnerability of urban areas to be analyzed, which has been primarily addressed by the estimation of economic losses or, more recently, including a few economic variables within social vulnerability assessments. Thus, 118 economic variables were initially gathered and then divided into groups through a hierarchical segmentation analysis. Subsequently, variables were combined employing a principal components analysis, giving rise to the economic vulnerability factors that were subsequently aggregated to construct the IEVI. Tolerance statistic was used as a weighting method to define the IEVI, whereas quintiles were chosen as a statistical criterion to map economic vulnerability. As a final step, latent class cluster analysis was implemented to identify spatial patterns of vulnerability. Our findings show that IEVI scores have a high spatial variability and a high degree of complexity in the relationships among different vulnerability factors. Moreover, they help to identify spatial patterns of vulnerability, which makes the design of suitable vulnerability reduction strategies possible, thereby improving the efficiency of flood risk management plans and policies.

Floods have prevailed in the recent years, hampering not only social but also the economic development as well. This global pandemic has caused loss of lives, property and economic damages in many countries, including Zimbabwe. Rainfall intensity in the country's seven main river catchments namely; Mzingwane, Gwayi, Save (or Sabi), Mazowe (or Mazoe), Sanyati, Manyame and Runde triggers flash floods due to high peak discharges. It is therefore of paramount importance to try and reduce or rather prevent these losses due to flood events. The main objective of this study is to ascertain flood events in Zimbabwe and discuss how best they can be managed for a sustainable future. The assessment is carried out using AQUEDUCT Global Flood Analyzer in which all the analysis is based on the Gross Domestic Product (GDP), population and the present and future (2030) urban damage. To estimate future changes and effectively suggest flood disaster management and mitigation strategies, three scenarios obtained from the Intergovernmental Panel on Climate Change 5th Assessment Report were utilized. A 5-year flood protection was then employed and the urban damage due to the flood events, the population at risk and the effects of this disaster on GDP was determined. This study outlined that in any given year, the majority of Zimbabwe has a low to a medium that is 2–3% probability of flood occurrence in which a 5-year flood has a 20% occurrence probability in any given year. If there is no flood protection employed, this 5-year flood could cause $106.3 thousand affected population, $32.4 million urban damage and $67.9 million affected GDP. It is concluded that it is impossible to completely eliminate flood events, however, proposed mitigation measures, diminution approach and proper planning and preparation before their occurrence can reduce the environmental, economic and social losses.

The purpose of this paper is to investigate information seeking behaviour of people involved in slow and flash flood disasters, specifically how they received the first alert, where they then turned for more information, and what their main sources and forms were. An online and mailed survey based on models of problem-specific information seeking and risk information for natural hazards secured responses from Australians who had experienced flash flood (n = 91) and slow flood (n = 41). It found that information pathways taken by individuals are different for slow and flash floods, but the set of information forms and sources used are similar. ‘Other people’, television and news and weather websites were predominant sources and forms in flash flood, and online sources, television and radio predominant in slow flood. The importance of other people and mainstream media (including their online sites) in information behaviour means that mainstream media should remain an important component of information efforts by agencies. This study builds further evidence that disaster type and the media landscape should be taken into account when developing warning and response communication strategies, and allows public information officers to prioritise communication forms during response.

The objective of this research is to improve the understanding and recognition of the management challenges to flash flooding hazards and the potential adaptive measures within the arid urban areas through a socio-hydrological framework. Considering the capital of Sudan, Khartoum, as an example of urban arid areas with increasing flash flood risk, the analysis was founded on expert views and opinions collected from a range of different flood management actors following the 2013 and 2014 flash flood events. The qualitative research methods included participant observation, expert interviews and focus groups. The main themes of management challenges recorded included weak institutional capacity, bad governance, limited resources, and poor urban planning. These four themes, in turn, included different types of challenges, among which lack of: civil society engagement and coordination of actors, political will, data and tools, and effective urban development strategy shared the highest number of comments from the professional actors in each theme, respectively. These findings presented a management perspective to the lessons previously established and learned from an impact assessment. Accordingly, the amalgamation of all the lessons learned from the flood research findings enabled a suitable Master Flash Flood Management Plan (MaFFMaP) to be proposed as a final product. This plan would operate within an Integrated Flash Flood Management (IFFM) framework. The facets of the MaFFMaP include steps toward improving the quantity and quality of data resources regarding this hazard, aspects for use of these new datasets within a mixed-measure (structural and non-structural) approach from the authorities, and programmes for building community and civil society capacity through improving awareness and engagement. Furthermore, it is intended that this plan would be a replicable design, which could therefore be adopted and implemented in the wider context of the urban arid regions.

Research on urban flood hydrology—especially in small watersheds—is urgently needed in response to a dearth of small catchment studies, rapid urban growth, increased flash flooding, and precipitation variability. This study compares stormflow between three small catchments in the South Carolina Sandhills of the USA: two heavily urbanized, and one forested catchment that serves as a proxy for pre-urban conditions. Comparisons of runoff volume, runoff coefficient, peak discharge, and shape of dimensionless unit hydrographs (DUH) show significantly larger stormflow volume and peak instantaneous discharge in the urban catchments that exceed those in the forested catchment by more than an order of magnitude. Changes in hydrograph shapes are visualized by DUHs and measured by skewness and kurtosis. Urban kurtosis values of DUHs are significantly higher than forested kurtosis values (p-values

The recent acceleration of gully erosion caused by environmental factors and human impacts has led to an enhanced demand for applied research in risk-prone areas worldwide. We investigated the dynamics of gullies that have recently threatened dwellings and railways in the foreland of the Eastern Sudetes (340–390 m a.s.l. in the NE part of Czechia). Flood countermeasures in a residential area above the study site created conditions conducive to accelerated erosion in the gullies; thus, the main aim of this study was to determine how human interventions changed the spatio-temporal dynamics of the gullies during a short period. Twenty two gullies (with a mean length 48.5 m) have developed on a 1-km-wide escarpment (with a mean slope 25°) composed of glaciogenic sediments of various sizes. Dendrogeomorphic techniques were applied on 23 exposed roots of Tilia cordata Mill. (a tree species that has never been used to detect root exposure). Microsections were prepared using a G.S.L.1 sledge microtome and analysed using the WinCELL Reg software to determine the timing of root exposure. Approximately 90% of the eroded sediments (1287.4 m3) were transported across the railway onto the floodplain and caused damage to dwellings, while approximately 10% created bare accumulations at the gully floors. The most significant pulses of gully erosion occurred during the last 10 years (2007, 2009, 2010, and 2014). The maximum identified gully erosion occurred in 2014 (max. incision: 154 cm; maximum widening: 160 cm). In contrast, the development of the bank failures has been slowly progressing since the early 1990s, with a mean bank eroded area between 0.07 and 0.12 m2 year−1. The analysis of the precipitation characteristics (1963–2016) with the Mann-Kendal trend test revealed no significant trend. However, the last strong erosion event, in May of 2014, was triggered by an extraordinary rainstorm with an hourly intensity of 41.3 mm h−1 (maximum intensity of 2.8 mm min−1). Therefore, the recent increase in gully erosion is the consequence of extreme precipitation and human interventions that have been performed in the study site since 2007 (i.e., damming of the ditches and building of new culverts). The dendrogeomorphic research of exposed T. cordata roots significantly contributed to the identification of the gully erosion pulses and thus can be further applied in other localities.