Extreme Flood Events Research Articles

Salinization of stream water and groundwater at daily to decadal scales in a temperate climate

AbstractElevated salt concentrations in streams draining developed watersheds are well documented, but the effects of hydrologic variability and the role of groundwater in surface water salinization are poorly understood. To characterize these effects, we use long‐term data (12–19 yr) and high‐frequency specific conductance (SPC) data collected from 13 streams across New Hampshire, USA. Concentration–discharge (C–Q) relationships for chloride (Cl−) derived from high‐frequency SPC showed distinct seasonal variability. Diluting behavior was common, but flushing behavior occurred in autumn and winter, suggesting that both groundwater and surface runoff contribute salts to streams. Long‐term data show that although extreme flood events initially reduced salt concentrations in groundwater and rural streams, concentrations recovered to preflood conditions in about a decade. Chronic Cl− exceedances occurred in urban streams during all seasons. This research suggests that variation in stream flow, extreme events and application of deicing agents play a role in freshwater salinization.

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Persistent and nonpersistent regional extreme total, daytime, and night‐time precipitation events over southwest China (1961–2019)

AbstractExtreme persistent precipitation is becoming increasingly common globally, and persistent extreme regional precipitation events (PERPEs) pose a particularly serious threat to humans and environmental systems. This study investigated total precipitation (TP), daytime precipitation (DP), and night‐time precipitation (NP) in southwest China (SWC) during 1961–2019. The occurrence of TP, DP, and NP was analysed under the conditions of persistence over 1–5 days, temporal persistence over >2 days, and temporal nonpersistence over ≤2 days, and spatiotemporal overlap for at least 3 days (i.e., a PERPE) using the objective identification technique for regional extreme events. The results indicated the following. (a) Annual maximum daily precipitation ≥200 (100) mm in terms of TP (NP) was recorded mainly in the Sichuan Basin (SCB) and eastern parts of the Yunnan–Guizhou Plateau (YGP), and it occurred mostly in summer. For DP, annual maximum daily precipitation of ≥100 mm was recorded throughout SWC, and it occurred mainly in winter in the Henduan Mountains, summer in the SCB, and spring in western parts of the YGP. (b) The magnitudes of NP and DP differed for events persisting for 1–5 days. The average amount of precipitation with temporal persistence increased during 1961–2019 for TP, DP, and NP. However, the frequency of occurrence of events with temporal persistence increased more in comparison with that of events with temporal nonpersistence. Overall, the frequency of occurrence of events with temporal persistence or temporal nonpersistence in the western SCB and eastern YGP increased more for TP and NP than for DP. (c) In the study period, 22, 44, and 4 PERPEs were detected for TP, NP, and DP, respectively, occurring mainly in the SCB, indicating that TP was dominated by night‐time PERPEs. These findings improve understanding of PERPEs changes in SWC and provide scientific support for implementation of measures intended to prevent and mitigate extreme flood events and waterlogging.

Flood Simulation and Flood Risk Reduction Strategy in Irrigated Areas

The potential risk of flood or waterlogging in irrigation districts has increased due to global climate change and intensive human activities. This paper employed a waterlogging process simulation model for flat irrigation districts in the paddy fields to simulate floods under different scenarios. The scenarios of the rainfall conditions, initial storage depths, and work scales are designed, respectively. The risk of flood damage increases as rainfall increases, with a maximum increase of 62.8%, comparing the extreme scenario with the current scenario. A moderate rise in pumping station flow and using pre-rain drainage measures in the paddy fields can effectively reduce waterlogging loss. The total regional flood damage was reduced by up to 10.9%, 15.8%, and 35.9% when the pump station flow in the study area was increased by 10%, 20%, and 30%. The insights from this study of the possible future extreme flood events may help flood control planning.

Multi-Hazard property buyouts: Making a case for the acquisition of flood and contaminant-prone residential properties in Galena Park, TX

The aftermath of extreme flood events can be particularly devastating for residential communities in proximity to flood-prone petrochemical facilities, as they are likely to experience multiple impacts from a single flood event. Hazard impacts could be from flood inundation to their properties, and floodwaters carrying contaminants from nearby facilities into their homes. While property acquisition or buyouts have been effectively used as a flood mitigation strategy, current buyout selection processes only factor in flood exposure, thereby ignoring other hazards such as exposure of properties to potential chemical substance transfer. In this paper, we identify properties that are eligible for flood buyouts but are also at a high risk of contaminant transferal during extreme flood events. We apply a benefit–cost analysis methodology to assess the economic viability of buyouts and proximity metrics to prioritize buyouts of contaminant-prone properties in Galena Park, Texas. Results indicate that, in selected flood-only property acquisition scenarios, cumulative avoided flood losses exceed the cost of property acquisition. However, although with lower cost-benefit values, a selection criterion that factors a combination of flood and contaminant-prone properties as buyouts results in multiple properties being removed from harm’s way. Our findings emphasize the potential economic benefits of applying a multi-hazard selection criterion in dealing with flood property buyouts, especially in socially vulnerable communities with high exposure to both flooding and contaminant transfer.

Neglecting Model Parametric Uncertainty Can Drastically Underestimate Flood Risks

AbstractFloods drive dynamic and deeply uncertain risks for people and infrastructures. Uncertainty characterization is a crucial step in improving the predictive understanding of multi‐sector dynamics and the design of risk‐management strategies. Current approaches to estimate flood hazards often sample only a relatively small subset of the known unknowns, for example, the uncertainties surrounding the model parameters. This approach neglects the impacts of key uncertainties on hazards and system dynamics. Here we mainstream a recently developed method for Bayesian inference to calibrate a computationally expensive distributed hydrologic model. We compare three different calibration approaches: (a) stepwise line search, (b) precalibration or screening, and (c) the Fast Model Calibrations (FaMoS) approach. FaMoS deploys a particle‐based approach that takes advantage of the massive parallelization afforded by modern high‐performance computing systems. We quantify how neglecting parametric uncertainty and data discrepancy can drastically underestimate extreme flood events and risks. Precalibration improves prediction skill score over a stepwise line search. The Bayesian calibration improves the uncertainty characterization of model parameters and flood risk projections.

Which models for extreme flood events in Mediterranean catchments?

Over the last years, most of the Mediterranean countries have been affected by catastrophic flood events generated by never observed before extreme rainfalls. Those events are frequently convective and stationary for several hours. The recorded intensities have frequently values exceeding 100 mm/hour and can last for several hours. Under those specific conditions as during the storm ALEX of October 2020, the runoff processes are particularly intense and can generate massive floods. Mitigation strategies should be developed and based on modeling that can support the understanding of the processes and the forecast the magnitude of the flood events and the associated impacts. The choice of the relevant hydrological modeling tools is a key element. The selected ones should be able to provide the relevant information, on time and with the relevant accuracy for the decision makers. The hydrological deterministic distributed models have reached a sufficient maturity to provide an accurate representation of the processes. The storm ALEX was generating more than 500 mm in less than 6 hours and producing a devastating flood within the Vésubie valley (France) in October 2020. The analysis of the event has demonstrated the difficulty to obtain consistent field observations and the limitations of many stochastic hydrological tools. The application of the AquaVar approach, combining several distributed deterministic models, has demonstrated its capacity to generate meaningful hydrographs and to quantify process with the catchment. The proposed solution is currently implemented within a real-time decision support system and can be used in real-time.

Development of a Quantitative Approach for Morphodynamic Assessment of Extreme Flood Event in Lokoja

Abstract – This study developed a quantitative approach for the morphodynamic assessment of River Niger at Lokoja. The study involves the collection of twenty-one years daily discharge and water level at the gauging station. The data were collated and outliers were removed. The missing data were fitted using the Least Square Method. The flood generating processes were investigated by computing the bankfull discharge of selected reach as well as collecting river bed samples at six (6) different locations along the river reach. Based on these, the specific gravity and mobile D50 and D90 of the bed materials were obtained. The preliminary investigation of the river morphodynamics was studied by computing the sediment transport parameters such as Shield parameter, bed shear velocity, sediment fall velocity amongst others. These parameters are significantly important due the high flow rate associated with the river. Based on criteria by two well-known sediment transport capacity formula, the river reach is characterized as sandy-bed River in line with Eugelund and Hansen’s Formula (E-H-F). The entire flow generation parameters and mobile river bed materials failed the Meyer and Peter- Muller criteria. Hence, the sediment transport capacity of the river was computed using (E-H-F). The results show that understanding the morphodynamics of the rivers play a significant role in the understanding of flooding.

Assessment of inland flood hazard sensitivity to hydrological intensification in coastal watersheds

IntroductionIntensification of the hydrologic cycle induced by climate variability and landscape modification is expected to increase the frequency of extreme flood events. Multi-jurisdictional approaches to manage inland flood risks at watershed scales demand the ability to objectively assess not only future flood potentials, but to also set priorities based upon multiple factors such as the stream channels most sensitive to hydrologic stress.MethodsThis study presents a method to estimate flood hazard sensitivities to increasing stormwater runoff due to hydrologic intensification (e.g., urbanization, climate effects) on local and watershed scales. The method is demonstrated in the low-gradient inland watershed regions of southwestern coastal Louisiana, USA. Utilizing highly detailed numerical models from the Federal Emergency Management Agency (FEMA), absolute and relative flood sensitivities were calculated for 45 flood-prone stream channels in the Lafayette, LA region. Channel sensitivities to flood hazards induced by changes in the 10-yr (10% annual exceedance probability) flood flows were quantified by analysis of 485 scenarios developed using a downward counterfactual scaling strategy.Results and discussionRelying entirely upon publicly available numerical models and input datasets, the study revealed key information about the relationship between estimable hydraulic characteristics (e.g., conveyance, resistance, and flow) and absolute and relative flood hazard sensitivity measures on a per-channel basis. Information from the subset of detailed numerical models was efficiently leveraged to provide a regional map of relative flood sensitivities. The methodology is robust and can be applied in very general settings to address the concern of hydrologic intensification in practical flood risk management applications.

Urban Flood Loss Estimation and Evacuation Design Based on a 500-Year Extreme Flood Event in Syracuse City

To understand the potential risk of flooding in Syracuse City, New York State, USA, this research attempted to accomplish the flood hazard assessment for a simulated 500-year flood event in the downstream floodplain of Onondaga Creek within Syracuse. Based on the commonly used category of flood damages, the flood damage of Syracuse was divided into loss of buildings and loss of population. The results showed that the city’s center would have the highest damage rate for buildings and a total of 1139 buildings would be inundated, of which 326 buildings would be severely damaged by more than 80%. Furthermore, about 7390 people would be directly affected by the flood event, among which approximately 900 people might lose their lives. Communities near Onondaga Creek were assigned designated evacuation shelters based on the accessibility and distance to the shelters. The shortest available evacuation routes were calculated. More shelters should be provided in the central downtown area, with its large population, and distributed along the western bank of Onondaga Creek. This research offered a first approximate flood loss estimation that might lead to more attention and studies concerning a potential flood hazard in the future. It also provided science-based guidelines for city authorities to refer to in practical flood hazard mitigation.

Multiscale interactions driving the devastating floods in Henan Province, China during July 2021

The rare extreme flooding event in Henan Province, China, during July 2021 (referred to as the “21.7” flooding event) was attributable to persistent heavy rainfall boosted by an enhanced moist southeasterly flow and substantial moisture convergence. Based on analyses of the scale-decomposed moisture budget equation, we show that the 21.7 flooding event was a result of scale interactions between the monsoon mean field, intraseasonal oscillation, and synoptic disturbances. The two distinct modes of the boreal summer intraseasonal oscillation (10–30 and 30–90 days) unusually had a crucial combined role in moisture convergence, aided by the increased seasonal-mean moisture content, maintaining persistent rainfall from the development (July 17–19) to decaying (July 21–23) phases of the 21.7 flooding event. In contrast, synoptic-scale moisture convergence was the leading process during the peak phase of the flooding event (July 20), contributing to the extreme values. The state-of-the-art subseasonal-to-seasonal prediction models showed limited skills in predicting this extreme event one to two weeks in advance, partly because of their biases in representing the intraseasonal oscillation and multiscale interactions.

Analysis of Climate Variability and Trends in The Context of Climate Changes: Case Study in Terengganu

Uncertainty of climate extreme nowadays causes an alteration in the local climate trend and variability. Terengganu, Malaysia recorded series of extreme drought and flood events throughout a year affected by North-East monsoonwhich will change the next climate pattern. Thus, itwill be affectingthe long-term planning and sustainability that related to the water resources in the long-term. The objective of this study was to analyse the trend changes of rainfall and temperature at Kuala Terengganu, Malaysia due to climate changes impact. The trends changes were analysed usingMan-Kendall and Sen’s Slope. The climate projection result shows the annual mean temperature is expected to have decreasing trend until end of century. However,Mar to June are expected to bit higher than historical reach to 29oCby RCP8.5. Then it will be dropped to 24oC (-5% from historical) during Northeast monsoon. Consistent to the annual rainfall, it was expected to have increasingtrendover time. The highest increasing trendwas expected to occur on Nov toDec more than40% by RCP8.5.

Suspended sediment response to Nordic bioeconomy and climate change scenarios in a first-order agricultural catchment

Soil loss by erosion threatens food security and reduces the environmental quality of water bodies. Prolonged and extreme rainfalls are recognized as main drivers of soil erosion, and climate change predictions for large parts of the world foresee such increases in precipitation. Erosion rates are additionally affected by land use, which may change as a result of the shift from a fossil fuel-based economy to an economy relying on using renewable biomass, a “Bioeconomy”. In this study we aimed at investigating, through modelling, i) if future changes in land use, due to a bioeconomy, would increase the risk for soil loss and enhance suspended sediment yields in streams and ii) if these changes, when combined with climate change effects, would further aggravate suspended sediment conditions in a catchment. We used hydrological and bias adjusted climate models to compare the effect of seven land use pathways on discharge and sediment transport relative to a baseline scenario under present and future climate conditions. The study was carried out based on data from a small headwater stream, representative for cereal production areas of S-E Norway. By modelling our scenarios with the PERSiST and INCA-P models, we found that land use change had a greater influence on both future water discharge and sediment losses than a future climate. Changes from climate showed strongest differences on a seasonal basis. Out of the modelled land use pathways, a sustainable pathway manifested the least occurrence of extreme flood and sediment loss events under future climate; whereas a pathway geared towards self-sufficiency indicated the highest occurrence of such extreme events. Our findings show that careful attention must be placed on the land use and soil management in the region. To maintain freshwater quality, it will be increasingly important to implement environmental mitigation measures.

A data-driven spatial approach to characterize the flood hazard.

Model output of localized flood grids are useful in characterizing flood hazards for properties located in the Special Flood Hazard Area (SFHA-areas expected to experience a 1% or greater annual chance of flooding). However, due to the unavailability of higher return-period [i.e., recurrence interval, or the reciprocal of the annual exceedance probability (AEP)] flood grids, the flood risk of properties located outside the SFHA cannot be quantified. Here, we present a method to estimate flood hazards that are located both inside and outside the SFHA using existing AEP surfaces. Flood hazards are characterized by the Gumbel extreme value distribution to project extreme flood event elevations for which an entire area is assumed to be submerged. Spatial interpolation techniques impute flood elevation values and are used to estimate flood hazards for areas outside the SFHA. The proposed method has the potential to improve the assessment of flood risk for properties located both inside and outside the SFHA and therefore to improve the decision-making process regarding flood insurance purchases, mitigation strategies, and long-term planning for enhanced resilience to one of the world's most ubiquitous natural hazards.

A hydraulic modelling approach to study flood sediment deposition in floodplain lakes

AbstractAbandoned river channels on alluvial floodplains represent areas where sediments, organic matter, and pollutants preferentially accumulate during overbank flooding. Theoretical models describing sedimentation in floodplain lakes recognize the different stages in their evolution, where the threshold for hydrological connectivity increases in older lakes as a plug‐bar develops. Sedimentary archives collected from floodplain lakes are widely used to reconstruct ecological and hydrological dynamics in riverine settings, but how floodplain lake evolution influences flow velocities and sedimentation patterns on an event scale remains poorly understood. Here we combine sediment samples collected in and around a floodplain lake with hydraulic modelling simulations to examine inundation, flow velocity, and sedimentation patterns in a floodplain lake along the Trinity River at Liberty, Texas. We focus our analyses on an extreme flood event associated with the landfall of Hurricane Harvey in August 2017 and develop a series of alternative lake bathymetries to examine the influence of floodplain lake evolution on flow velocity patterns during the flood. We find that sediments deposited in the lake after the Hurricane Harvey flood become thinner and finer with distance from the tie‐channel in accordance with simulated flow velocities that drop with distance from the tie‐channel. Flow velocity simulations from model runs with alternative plug‐bar geometries and lake depths imply that sedimentation patterns will shift as the lake evolves and infills. The integration of sediment sampling and hydraulic model simulations provides a method to understand the processes that govern sedimentation in floodplain lakes during flood events that will improve interpretations of individual events in sedimentary archives from these contexts.

Effect of dam discharges and tides to transport of Yangtze River using coastal acoustic tomography systems

The streamflow characteristics within the Yangtze River Basin have experienced substantial fluctuations in recent years because of the combined effects of environmental factors and intensive human activities. In this study, at the Datong station, two coastal acoustic tomography (CAT) systems were used to track the Yangtze River discharge from July 2018 to January 2021. The stage–discharge relationship presented large uncertainties because of the Three Gorges Dam (TGD) operations, whereas the CAT method performed effectively in discharge monitoring even during extreme flood events. The distribution of downstream discharge was concentrated because of the regulation by the TGD. Analysis of the potential drivers in the downstream river hydrology reveals that the effect of rainfall events (leading to a maximum of ~40% changes) was heavily influenced by the regulation by the TGD (at least 50% contribution). Additionally, the river–tide process is also sensitive to the discharge regulated by the TGD. The discharge induced by tidal waves was negligible (a maximum of 1.11% change). This work demonstrates that an acoustic method can effectively monitor the massive flood discharge in unsteady flow conditions in large rivers, thereby facilitating the management of large-scale dam- and tide-influenced river systems.

Enhancement of river flooding due to global warming

Human-induced climate change has increased the frequency and intensity of heavy precipitation1. Due to the complexity of runoff generation and the streamflow process, the historical impact of human-induced climate change on river flooding remains uncertain. Here, we address the question of whether anthropogenic climate change has altered the probability of the extreme river flood events for the period 1951–2010 based on simulated river discharge derived from large ensemble climate experiments with and without human-induced climate change. The results indicate that human-induced climate change altered the probabilities of 20 of the 52 analyzed flood events. Fourteen of these 20 flood events, which occurred mainly in Asia and South America, were very likely to have been enhanced by human-induced climate change due to an increase in heavy precipitation. Conversely, two flood events in North/South America and two flood events in Asia and two flood events in Europe were suppressed by human-induced climate change, perhaps as a result of lower snowfall. Human-induced climate change has enhanced flooding more prominently in recent years, providing important insights into potential adaptation strategies for river flooding.

Climate Change and Its Impact on the Agricultural Calendar of Riverine Farmers in Médio Juruá, Amazonas State, Brazil

The labor relationship developed by the Amazonian riverside dwellers is weakened due to changes in temperature, the flood pulse, the ebb tide of the rivers, and precipitation. In this context, this research aimed to evaluate the impacts of climate change on the socio-biodiversity chains in the region of Médio Juruá-Amazonas. Collections were carried out in two communities located in the Sustainable Development Reserve (RDS) Uacari, in July 2022, through participatory workshops. The communities affirm that the extreme flood events of the Juruá River are more intense in recent years, both concerning the extreme levels of the river and in periodicity and speed of flooding. The large floods have impacted the productive calendar, generating losses for farmers. In addition, rubber trees and cassava plantations have been dying with the large floods, and oil seeds are being carried by the water before harvest. The physical data of the Juruá River shows a trend of increasing extreme floods over the last 40 years for the period November to April, highlighting the years 2013 to 2015 and 2021 with the largest positive anomalies. Farmers have adapted their calendars, modified some planting areas to locations with higher altitudes and farther from the river banks, and have sought new rubber matrices. The results point to the need for mitigation and adaptation measures promoted by local governments.

Extreme climatic events and human biology and health: A primer and opportunities for future research.

Extreme climatic events are increasing in frequency, leading to hotter temperatures, flooding, droughts, severe storms, and rising oceans. This special issue brings together a collection of seven articles that describe the impacts of extreme climatic events on a diverse set of human biology and health outcomes. The first two articles cover extreme temperatures extending from extreme heat to cold and changes in winter weather and the respective implications for adverse health events, human environmental limits, well-being, and human adaptability. Next, two articles cover the effects of exposures to extreme storms through an examination of hurricanes and cyclones on stress and birth outcomes. The following two articles describe the effects of extreme flooding events on livelihoods, nutrition, water and food insecurity, diarrheal and respiratory health, and stress. The last article examines the effects of drought on diet and food insecurity. Following a brief review of each extreme climatic event and articles covered in this special issue, I discuss future research opportunities-highlighting domains of climate change and specific research questions that are ripe for biological anthropologists to investigate. I close with a description of interdisciplinary methods to assess climate exposures and human biology outcomes to aid the investigation of the defining question of our time - how climate change will affect human biology and health. Ultimately, climate change is a water, food, and health problem. Human biologists offer a unique perspective for a combination of theoretical, methodological, and applied reasons and thus are in a prime position to contribute to this critical research agenda.

Topical and emotional expressions regarding extreme weather disasters on social media: a comparison of posts from official media and the public

Understanding media frames and the public resonance during disasters is essential for making inclusive climate change and adaptation policies in the context of increasingly extreme weather events. In this study, we use the extreme weather and flood event that occurred in July 2021 in Zhengzhou, China, as a case study to investigate how official media in China reported this event and how the public responded. Moreover, since one accountability investigation report regarding this disaster was released in January 2022, we also compared these posts between the emergency response period and the post-crisis learning period after the report’s release. Topic modeling using the LDA (Latent Dirichlet Allocation) method and emotion analysis were conducted to analyze the posts from Weibo, China’s primary social media platform. The results demonstrated that the posts from official media and the public comments differed in both topics and emotions, with relatively little coherence. During the emergency response period, the media’s posts focused more on the facts, such as the extreme weather event, the places where it occurred, the impacts, and the search and rescue efforts, while the public comments were more about help appeals from the neglected ones in the rural areas, and emotional expressions such as moral support, condolence or encouragement to the victims and their families. After the accountability investigation in January, the media’s posts primarily covered the investigation process, the punishment, the attribution of disaster consequences, and the lessons learned, while the public’s comments were relatively emotional, praised the good, condoled the victims, and condemned the villains. The dominant emotion from the media’s posts was “like” in July 2021, but it became depression in January 2022. Anger was the prevalent emotion from the public during all the stages. This study provided valuable knowledge to the current understanding of the different patterns and dynamics of official media reports and the public’s resonance in disaster management.