Extreme Flood Events Research Articles

An efficient and economic desilitation strategy for reservoir sustainable development under the threat of extreme flooding threaten

Abstract Severe sediment disaster has already been observed locally and worldwide, and serious disasters will happen increasingly in the future due to climate change. Hence, developing a proper reservoir desilitation strategy is an urgent priority to ensure sustainable water resources development worldwide. This study aims to investigate the release efficiency of the bypass tunnel in the reservoir. Firstly, a 2D numerical model was adapted to reproduce the most severe sedimentation disaster due to Typhoon Aere and obtain a reliable result compared with the measured data. Then, the concept of climate change was embedded to understand the release capability of the bypass tunnel under slight to worst scenarios. Finally, the bypass tunnel is demonstrated to be effective in releasing sediment during typhoon periods and prolonging the reservoir lifespan. In conclusion, this study proposes a proper solution to reservoir sedimentation during extreme flooding events. The optimization of water resources and economic benefits can help reservoir management achieve the goal of sustainable development. The presented research can be promoted in the worldwide reservoir to face the possibly severe sediment disaster under the threat of climate change.

Decomposition of water vapor flux divergence and its application to a blizzard event over Ili Valley in Central Asia during 30 Nov to 1 Dec 2018

Central Asia is experiencing an increase in the occurrence of extreme flood events while still featuring in scarce precipitation. These extreme events are governed by weather systems of various scales as well as complex terrain effects. It is therefore difficult to analyze and forecast precipitation with traditional methods. In this study, an approach is designed by decomposing water vapor flux divergence (Qvall) under model's terrain following coordinates following the Helmholtz theorem. The traditionally used but important variable for depicting anomalous precipitation, Qvall, is partitioned into three components, i.e., flow divergence (Qvdiv), moisture advections by large-scale motion (QvL) and by sub-synoptic motion (QvS). Applications to a blizzard event occurred over Ili Valley during 30 Nov to 1 Dec 2018 is performed as an example. The eastward water vapor flux brings moisture from Balkhash Lake to Ili Valley during the entire precipitation event, while Qvall fails to indicate the initiation and weakening of precipitation. Temporal and spatial evolutions of the three decomposed components are analyzed with comparison to precipitation on both windward slope and lee side. Qvdiv with dominant magnitude always converges no matter precipitation intensifies or weakens, and therefore leads to false moisture aggregation signals in Qvall. The other two components, QvL and QvS, converge prior to precipitation and diverge or weaken before the event ends. Besides, QvL performs better than QvS on windward slope and shows moisture transport from upper levels while QvS achieves better on lee side. Future applications of this flow decomposition approach may thus extend to improving precipitation predictions with negligible computational costs over complex topography in other places around the world.

Extreme Flood Events in India and Attribution to Climate Change: An Analysis of News Media Coverage from 2013–2019 during Bihar Floods

AbstractThis study analyzes the news media coverage of floods in a major flood-prone state of India, Bihar. Although news media helps shape public perception and political actions, little analysis ...

Water stress resilient cereal crops: Lessons from wild relatives.

Cereal crops are significant contributors to global diets. As climate change disrupts weather patterns and wreaks havoc on crops, the need for generating stress‐resilient, high‐yielding varieties is more urgent than ever. One extremely promising avenue in this regard is to exploit the tremendous genetic diversity expressed by the wild ancestors of current day crop species. These crop wild relatives thrive in a range of environments and accordingly often harbor an array of traits that allow them to do so. The identification and introgression of these traits into our staple cereal crops can lessen yield losses in stressful environments. In the last decades, a surge in extreme drought and flooding events have severely impacted cereal crop production. Climate models predict a persistence of this trend, thus reinforcing the need for research on water stress resilience. Here we review: (i) how water stress (drought and flooding) impacts crop performance; and (ii) how identification of tolerance traits and mechanisms from wild relatives of the main cereal crops, that is, rice, maize, wheat, and barley, can lead to improved survival and sustained yields in these crops under water stress conditions.

Hydrodynamic Study of the Impact of Extreme Flooding Events on Wastewater Treatment Plants Considering Total Water Level

AbstractClimate change, sea level rise, and storm surge events are now significant factors threatening critical water and wastewater infrastructure. Extreme storm events have increased the need for...

Effects of extreme flooding on aquatic vegetation cover in Shengjin Lake, China

AbstractAquatic plants are the main primary producers and an important part of the aquatic ecosystem. Seasonal flooding broke out in July 2020 in the middle and lower reaches of the Yangtze River, resulting in continued high water levels in lakes connected to the Yangtze River. To study the impact of extreme flooding on aquatic vegetation cover, we utilized two methods (surveying and remote sensing image data) to determine the changes in the aquatic vegetation cover of Shengjin Lake, one of the lakes connected to the Yangtze River, during the wet season from 2018 to 2020. The results showed that the dominant aquatic plant species before the flood in July 2020 were the emergent plant Zizania caduciflora, the floating plant Trapa incisa, the submerged plant Ceratophyllum demersum and Vallisineria natans. The area covered by aquatic vegetation in 2018–2019 showed a slight upward trend, increasing from 24.94 to 25.94 km2. In April 2020, the aquatic vegetation cover was 25.53 km2, and after the flooding in July 2020, the aquatic vegetation cover decreased sharply to 1.36 km2, which was mainly composed of emergent plant Z. caduciflora in the nearshore. No recovery of the dominant aquatic plant species, the floating plant T. incisa and other submerged plants, was seen during the monitoring of water level decline from September to December 2020. Winter wetland plants were not significantly affected by flooding. The results of the study provide a theoretical basis for the maintenance mechanism of aquatic vegetation and lake management in Shengjin Lake.

Extreme floods in Europe: going beyond observations using reforecast ensemble pooling

Abstract. Assessing the rarity and magnitude of very extreme flood events occurring less than twice a century is challenging due to the lack of observations of such rare events. Here we develop a new approach, pooling reforecast ensemble members from the European Flood Awareness System (EFAS), to increase the sample size available to estimate the frequency of extreme local and regional flood events. We assess the added value of such pooling, determine where in Central Europe one might expect the most extreme events, and evaluate how event severity is related to physiographic and meteorological catchment characteristics. We work with a set of 234 catchments from the Global Runoff Data Centre matched to EFAS catchments and for which the performance of simulated floods is good when compared to observed streamflow. We pool EFAS-simulated flood events for 10 perturbed ensemble members and lead times ranging from 22 to 46 d, where flood events are only weakly dependent (<0.25 average correlation across lead times). The resulting large ensemble (130 time series instead of 1) enables the analyses of very extreme events which occur less than twice a century. We demonstrate that such ensemble pooling produces more robust estimates with considerably reduced uncertainty bounds (by ∼80 % on average) than observation-based estimates but may equally introduce biases arising from the simulated meteorology and hydrological model. Our results show that, for a given return period, specific floods are highest in steep, cold, and wet regions and are comparably low in regions with strong flow regulation through dams. Furthermore, our pooled flood estimates indicate that the probability of regional flooding is higher in Central Europe and Great Britain than in Scandinavia. We conclude that reforecast ensemble pooling is an efficient approach to increase sample size and to derive robust local and regional flood estimates in regions with good hydrological model performance.

An examination of extreme floods, effects on land-use change and seasonality in the lower St. Johns River Basin, Florida using HSPF and statistical methods

As population growth and urbanization are steadily rising, the need for dependable flood estimation techniques is crucial. This study evaluates extreme flood events in select sub-basins of the Lower St. Johns River in Florida, USA. The study considers the effect of urbanization on the natural hydrologic processes and flood magnitudes in the watershed. Additionally, the effects of varying seasonality into the hydrologic modeling procedure are also investigated. This research focuses on determining the 10-, 25-, 50-, and 100-year return frequency flood flows in Julington Creek, Ortega River, and Pablo Creek of the Lower St. Johns River Basin in Florida, USA. The major findings of this research indicate that by implementing a range of flood estimation methods one can better describe the inherent uncertainty with traditional estimates. Also, the research showed that varying seasonality in the hydrologic modeling procedure does not result in vast differences in the resulting flood estimates. However, various land-use scenarios may produce simulated flood flows of greater magnitude—especially when a more urbanized land-use scenario is modeled.

Changes of Chinese Coastal Regions Induced by Land Reclamation as Revealed through TanDEM-X DEM and InSAR Analyses

Chinese coastal topography has changed significantly over the last two decades due to human actions such as the development of extensive land reclamation projects. Newly-reclaimed lands typically have low elevations (<10 m) and often experience severe ground subsidence. These conditions, combined with the more frequent occurrence of extreme sea-level events amplified by global climate change, lead to an increased risk of flooding of coastal regions. This work focuses on twelve Chinese coastal areas that underwent significant changes from 2000 to 2015 in their environments, correlated to relevant land reclamation projects. First, the ground changes between 2000 and 2015 were roughly computed by comparing the TanDEM-X and the Shuttle Radar Topography Mission (SRTM) digital elevation models of the investigated areas. These results indicate that six of the analyzed coastal zones have reclaimed more than 200 km2 of new lands from 2000 to 2015, with five of them in northern China. Second, we focused specifically on the city of Shanghai, and characterized the risk of flood in this area. To this purpose, two independent sets of synthetic aperture radar (SAR) data collected at the X- and C-band through the COSMO-SkyMed (CSK) and the European Copernicus Sentinel-1 (S-1) sensors were exploited. We assumed that the still extreme seawater depth is chi-square distributed, and estimated the probability of waves overtopping the coast. We also evaluated the impact on the territory of potential extreme flood events by counting the number of very-coherent objects (at most anthropic, such as buildings and public infrastructures) that could be seriously affected by a flood. To forecast possible inundation patterns, we used the LISFLOOD-FP hydrodynamic model. Assuming that an extreme event destroyed a given sector of the coastline, we finally computed the extent of the flooded areas and quantified its impact in terms of coherent structures potentially damaged by the inundation. Experimental results showed that two coastline segments located in the southern districts of Shanghai, where the seawalls height is lower, had the highest probability of wave overtopping and the most significant density of coherent objects potentially subjected to severe flood impacts.

The extensive mercury contamination in soil and legacy sediments of the Paglia River basin (Tuscany, Italy): interplay between Hg-mining waste discharge along rivers, 1960s economic boom, and ongoing climate change

PurposeThe extensive Hg contamination in soil and sediments occurring along the Paglia River (Central Italy) is the result of the interplay between the geomorphological changes of the river and anthropic activities, primarily associated to the exploitation of Hg-deposits in "The Monte Amiata mining district" (MAMD). The present study determines the implications of the morphological changes that occurred along the Paglia River in the last 200 years on the distribution of Hg along the floodplain and riverbed, which today represent one of the main Hg-reservoirs in the MAMD.Materials and methodsThe temporal changes of the Paglia riverbed and the extent of its alluvial deposits were reconstructed by a GIS-based analysis of the available maps and aerial photos. The Hg-concentration in soil and sediment samples, collected along five transects transverse to the Paglia River channel, was determined by ICP-MS.Results and discussionSamples along the investigated Paglia River segment typically show Hg-contents exceeding the Italian threshold for residential and public green soil use (1 mg kg−1). The distribution of Hg in the Paglia floodplain results from the combination of exceedance of sediment yield to the river during mining activities, that fed the floodplain with large amounts of Hg-contaminated sediments during its braided stage about 100 years ago, and the morphological changes of the river, that led to the evolution from a braided to the present-day single channel river. The magnitude of the extension of Hg-contamination, the river geomorphologic changes, and the processes of transport, deposition, and re-suspension did not allow a natural “clean up” of the river system, which shows a low resilience. Under high flow conditions, and especially in coincidence with intense rain events, large amounts of Hg stored in the overbank sediments are mobilized and redistributed, contributing to make the floodplain a secondary Hg-source. Extreme weather events, expected to intensify as a consequence of climate change, will contribute to the recurrent distribution of Hg-contaminated legacy sediments in the floodplain and along the Paglia river course.ConclusionFrom a water/land management perspective, the variability of the river flow, associated with an increase of extreme flood events driven by climate change, will affect the distribution of Hg-contaminated particles in the Paglia River, contributing to the Hg input into the Mediterranean Sea in the future.Graphical abstract

Investigating hydrological model versatility to simulate extreme flood events

We adapted a semi-distributed hydrological model (GRSD) to improve its versatility to simulate flood events occurring under different conditions, especially flash-floods after dry summer periods in the Mediterranean region. The adaptation introduces a dependency on rainfall intensity in the production function. The evaluation over 2008-2018 in the Aude catchment (France) showed that the new model structure does not deteriorate long-term model simulations obtained from the original model. The adapted model performed better than or equal to the original model in terms of differences in the timing of peak discharges, regardless of the season of the year when the flood occurs. The most important improvement was observed in the simulation of the magnitude of the flood peaks during autumn floods. A visualisation of model versatility allows detecting the time steps when the new model tends to behave more similarly or differently from the original model in terms of runoff production.

Growth and Wood Trait Relationships of Alnus glutinosa in Peatland Forest Stands With Contrasting Water Regimes.

Human-driven peatland drainage has occurred in Europe for centuries, causing habitat degradation and leading to the emission of greenhouse gases. As such, in the last decades, there has been an increase in policies aiming at restoring these habitats through rewetting. Alder (Alnus glutinosa L.) is a widespread species in temperate forest peatlands with a seemingly high waterlogging tolerance. Yet, little is known about its specific response in growth and wood traits relevant for tree functioning when dealing with changing water table levels. In this study, we investigated the effects of rewetting and extreme flooding on alder growth and wood traits in a peatland forest in northern Germany. We took increment cores from several trees at a drained and a rewetted stand and analyzed changes in ring width, wood density, and xylem anatomical traits related to the hydraulic functioning, growth, and mechanical support for the period 1994–2018. This period included both the rewetting action and an extreme flooding event. We additionally used climate-growth and climate-density correlations to identify the stand-specific responses to climatic conditions. Our results showed that alder growth declined after an extreme flooding in the rewetted stand, whereas the opposite occurred in the drained stand. These changes were accompanied by changes in wood traits related to growth (i.e., number of vessels), but not in wood density and hydraulic-related traits. We found poor climate-growth and climate-density correlations, indicating that water table fluctuations have a stronger effect than climate on alder growth. Our results show detrimental effects on the growth of sudden water table changes leading to permanent waterlogging, but little implications for its wood density and hydraulic architecture. Rewetting actions should thus account for the loss of carbon allocation into wood and ensure suitable conditions for alder growth in temperate peatland forests.

Strengthen resilience to rivers flooding by the drag reduction technique

Urban agglomerations face the risk of overflowing rivers due to intense urbanization in flood-prone areas and the climate change effects. Despite the important protective measures deployed to reduce the fluvial flooding risk, additional efforts are still needed. This work aims to propose a new complementary non-structural protection measure, used to reduce the river flooding risk. The study is part of the NABRAPOL (NEBRASKA POLYMER) project, which aims to improve knowledge of the drag reduction effect by adding polymers in open-channel flows. The addition of polymers, even in limited concentrations, allows high friction to decrease with the typical Manning coefficient reduced up to 45%. An application case on a real watercourse is presented in this article. Two measurement campaigns are carried out on a river along 30 km. Experimental devices are deployed, and non-intrusive hydraulic measuring instruments are installed at the study field. Surface velocities are evaluated by the Large-Scale Particle Image Velocimetry (LSPIV) technique, and water depth is measured using ultrasonic radar sensors over the river. Measurement results show that the addition of 20 ppm of polymers in the flows results in a marked drag reduction by decreasing the water depth to 18% of its initial depth. The drag reduction technique by addition of small concentrations of polymers can be considered as a new and effective method to reinforce the measures already deployed in the flood risk management strategy since it allows the water depth to be decreased thus avoid overflowing rivers in the extreme flooding event.

Different Hazards, Different Responses: Assessments of Flooding and COVID-19 Risks among Upstate New York Residents

The coronavirus disease 2019 (COVID-19) pandemic and extreme flooding events have recently taken enormous tolls. Drawing on research into differential risk responses across hazards, the authors examine how different social processes surrounding risk from flooding and COVID-19 shape how people respond to each hazard. Data from a household survey of 498 residents in two cities in the northeastern United States reveal that levels of concern and protective measures vary across the two hazards. Whereas climate polarization does not appear to influence flood risk responses, COVID-19 responses appear strongly polarized. However, having a known risk condition can offset Republicans’ doubts about COVID-19. In addition, whereas people of color express greater concern about flooding, white people take more protective measures, and women are more likely than others to take protective measures against COVID-19. Contrasting stakes, immediacy, dread, and polarization surrounding flooding and COVID-19 intersect with social inequalities to produce differing patterns of risk response.

Prediction of floodwater impacts on vehicle blockages at bridges using artificial neural network

During extreme flood events, various debris like floating vehicles can block the bridges in urban rivers and floodplains. Blockage of vehicles can influence the floodwater hydrodynamics and potentially on the flood risk implications. Such obstructions often raise upstream water levels with back water effects, causing more water to be redirected into nearby metropolitan areas. This study attempts at evaluating artificial neural network (ANN) model in predicting the variations in floodwater depths and velocities along the channel centreline based on the changes in flowrate and distances from the inlet. The floodwater depth and velocity variations were obtained for three different types of bridges at specified sites along the channel centreline with three incoming discharges. A multilayer feedforward neural network (FFNN) model was used to investigate the effects of discharge (Q) and distance, on depth variation rate (D) or velocity (V). Additionally, a comparison study was done between 2 input 1 output and 2 input 2 output i.e. single output (depth variation rate (D) or velocity (V) versus multi-output depth variation rate (D) and velocity (V) for all the three models of bridges that are blocked by vehicles. The study has applied 12 training algorithms (TA) in the ANN modelling to optimize the TA that is most suitable for the dataset of three different bridges. The optimization is based on the performance criterion namely regression (R), mean squared error (MSE), mean absolute error (MAE), mean absolute percentage (MAPE), accuracy and coefficient of determinant (R2). Bayesian regularization backpropagation (BR) training algorithm gives a highest accuracy when compared in all three bridges. The scenario 2 input 2 output gave greatest accuracy results compared to 2 input 1 output. The findings showed a reliable estimation of significant impacts on the flow propagations and the hydrodynamic processes along rivers and floodplains. This study can help the decision makers in effective river and floodplain management practices.

Rainfall anomalies and typhoid fever in Blantyre, Malawi.

Typhoid fever is a major cause of illness and mortality in low- and middle-income settings. We investigated the association of typhoid fever and rainfall in Blantyre, Malawi, where multi-drug-resistant typhoid has been transmitting since 2011. Peak rainfall preceded the peak in typhoid fever by approximately 15 weeks [95% confidence interval (CI) 13.3, 17.7], indicating no direct biological link. A quasi-Poisson generalised linear modelling framework was used to explore the relationship between rainfall and typhoid incidence at biologically plausible lags of 1-4 weeks. We found a protective effect of rainfall anomalies on typhoid fever, at a two-week lag (P = 0.006), where a 10 mm lower-than-expected rainfall anomaly was associated with up to a 16% reduction in cases (95% CI 7.6, 26.5). Extreme flooding events may cleanse the environment of S. Typhi, while unusually low rainfall may reduce exposure from sewage overflow. These results add to evidence that rainfall anomalies may play a role in the transmission of enteric pathogens, and can help direct future water and sanitation intervention strategies for the control of typhoid fever.

A Bayesian network approach for multi-sectoral flood damage assessment and multi-scenario analysis

Extreme weather and climate related events, from river flooding to droughts and tropical cyclones, are likely to become both more severe and more frequent in the coming decades, and the damages caused by these events will be felt across all sectors of society. In the face of this threat, policy- and decision-makers are increasingly calling for new approaches and tools to support risk management and climate adaptation pathways that can capture the full extent of the impacts. In this frame, a GIS-based Bayesian Network (BN) approach is presented for the capturing and modelling of multi-sectoral flooding damages against future ‘what-if’ scenarios. Building on a risk-based conceptual framework, the BN model was trained and validated by exploiting data collected from the 2014 Secchia River flooding event, as well as other contextual variables. Moreover, a novel approach to defining the structure of the BN was performed, reconfiguring the model according to expert judgment and data-based validation. The model showed a good predictive capacity for damages in the agricultural, industrial and residential sectors, predicting the severity of damages with a classification accuracy of about 60% for each of these assessment endpoints. ‘What-if’ scenario analysis was performed to understand the potential impacts of future changes in i) land use patterns and ii) increasing flood depths resulting from more severe flood events. The output of the model showed a rising probability of experiencing high monetary damages under both scenarios. In spite of constraints within the case study dataset, the results of the appraisal show good promise, and together with the designed BN model itself represent a valuable support for disaster risk management and reduction actions against extreme river flooding events, enabling better informed decision making.

Condiciones de habitabilidad ante inundaciones: el caso de Tuxtla Gutiérrez, Chiapas, México

At present, there are changes in the environment that favor the presence of extreme climatic phenomena such as floods, this exposure implies that the populations of urban areas suffer effects on their material assets, which limits their capacity for individual and / or family development. Given the lack of local territorial planning, the establishment of colonies was allowed on the banks of the Sabinal river and its tributaries that present episodes of flooding during the rainy season (Sistema Municipal de Protección Civil, 2015).   The study evaluates the habitability conditions of the urban population exposed to flooding, the city of Tuxtla Gutiérrez, Chiapas is taken as a reference, since historically it is a recurring problem during the summer. The methodology interrelates geostatistical, spatial and cartographic databases with hemerographic information sources based on the review of the literature for the construction of the general index, determined in dimensions that group social, economic, educational aspects, availability of basic services, goods with those that count the dwellings and their accessibility, etc., on a geographical scale of Urban Geostatistical Areas (AGEB).   The results obtained generated an index on the distribution of habitability conditions by urban Ageb, they are interrelated with spatial data on floods and their relationship with Sustainable Development Goal 11 (ODS), which proposes to improve infrastructure conditions in cities and towns. sustainable communities so that the inequality originated among the population exposed to future extreme flood events that occur in the different areas that make up the city is reduced.

Dynamic amplification responses of short span bridges considering scour and debris impacts

During extreme flooding events, bridges could experience large lateral displacements or even collapse due to either strong hydraulic forces or the effects of large waterborne debris, such as tree branches. The effects of waterborne debris on the structural behaviors of bridges include temporary accumulated dams and direct debris impacts. The additional lateral hydraulic forces and the acceleration of bridge scouring process due to temporary accumulated dams were investigated by researchers. Several debris impact force models were proposed to determine the loading effects applied on bridges. However, very few studies were conducted on the dynamic responses of bridges during flooding events considering the effects of large wood debris (LWD) as a combination of additional lateral hydraulic forces, foundation scour, and direct debris impacts. Therefore, the present study performed numerical analyses for bridges subjected to foundation scour and LWD impacts corresponding to flooding events. Besides, the effects of foundation scour and LWD impacts on the dynamic responses were simplified for bridge design purposes. Firstly, various short-span bridges with possible foundation scour depths due to debris accumulation were numerically simulated to obtain dynamic characteristics. Then, the hydraulic forces applied on the bridges were updated considering an extra blocking area due to debris accumulation. The collision forces due to floating woody debris were also introduced into the vehicle-bridge coupling system. Finally, the dynamic amplification factors (DAFs) with and without considering the effects of debris impacts were calculated and compared. It was found that the DAFs increase 20% at the maximum due to the effects of debris impacts. A modified factor was proposed to consider the effects. The reaction forces with and without the effects were also calculated to investigate the effects on the risk of deck unseating. Introducing possible debris impacts during flooding events into the dynamic analyses of bridges brings a more realistic estimation for the safety of bridges. The DAFs of bridges can be further taken as a guide for the supplements of design codes. The updated reaction forces would help to guide the risk mitigation of deck unseating.

Diamicton facies in the vicinity of Duhlata cave, Bosnek karst region, Southwestern Bulgaria

Karst caverns in the Upper Triassic dolostones of the Rusinovdel Formation are filled with allochthonous clastics (brecciaconglomerates with maximum boulder size) and locally with speleothems (flowstones). Deposition of the former (diamicton facies) by debris flows resulted from extreme flood events along the upper reaches of Struma river. The polymict material reflects erosion of various rock types in the source area but is dominated by resedimented Lower Triassic red beds. The diamictons are more or less similar to the few known examples from Quaternary karst caves.