scholarly journals Estimating extreme flood events – assumptions, uncertainty and error

2015 ◽  
Vol 369 ◽  
pp. 31-36 ◽  
Author(s):  
S. W. Franks ◽  
C. J. White ◽  
M. Gensen
Keyword(s):  
Flood Risk ◽  
Southern Oscillation ◽  
Exceedance Probability ◽  
Flood Events ◽  
Hydrological Extremes ◽  
Eastern Australia ◽  
Extreme Flood ◽  
Statistical Approaches ◽  
Conditional Estimates ◽  
Traditional Approaches

Abstract. Hydrological extremes are amongst the most devastating forms of natural disasters both in terms of lives lost and socio-economic impacts. There is consequently an imperative to robustly estimate the frequency and magnitude of hydrological extremes. Traditionally, engineers have employed purely statistical approaches to the estimation of flood risk. For example, for an observed hydrological timeseries, each annual maximum flood is extracted and a frequency distribution is fit to these data. The fitted distribution is then extrapolated to provide an estimate of the required design risk (i.e. the 1% Annual Exceedance Probability – AEP). Such traditional approaches are overly simplistic in that risk is implicitly assumed to be static, in other words, that climatological processes are assumed to be randomly distributed in time. In this study, flood risk estimates are evaluated with regards to traditional statistical approaches as well as Pacific Decadal Oscillation (PDO)/El Niño-Southern Oscillation (ENSO) conditional estimates for a flood-prone catchment in eastern Australia. A paleo-reconstruction of pre-instrumental PDO/ENSO occurrence is then employed to estimate uncertainty associated with the estimation of the 1% AEP flood. The results indicate a significant underestimation of the uncertainty associated with extreme flood events when employing the traditional engineering estimates.

scholarly journals Concurrent wet and dry hydrological extremes at the global scale

2020 ◽  
Vol 11 (1) ◽  
pp. 251-266 ◽  
Author(s):  
Paolo De Luca ◽  
Gabriele Messori ◽  
Robert L. Wilby ◽  
Maurizio Mazzoleni ◽  
Giuliano Di Baldassarre
Keyword(s):  
South America ◽  
Southern Oscillation ◽  
High Impact ◽  
Western China ◽  
Drought Severity ◽  
P Value ◽  
Worst Case ◽  
Hydrological Extremes ◽  
Eastern Australia ◽  
Eastern Russia

Abstract. Multi-hazard events can be associated with larger socio-economic impacts than single-hazard events. Understanding the spatio-temporal interactions that characterize the former is therefore of relevance to disaster risk reduction measures. Here, we consider two high-impact hazards, namely wet and dry hydrological extremes, and quantify their global co-occurrence. We define these using the monthly self-calibrated Palmer Drought Severity Index based on the Penman–Monteith model (sc_PDSI_pm), covering the period 1950–2014, at 2.5∘ horizontal resolution. We find that the land areas affected by extreme wet, dry, and wet–dry events (i.e. geographically remote yet temporally co-occurring wet or dry extremes) are all increasing with time, the trends of which in dry and wet–dry episodes are significant (p value ≪ 0.01). The most geographically widespread wet–dry event was associated with the strong La Niña in 2010. This caused wet–dry anomalies across a land area of 21 million km2 with documented high-impact flooding and drought episodes spanning diverse regions. To further elucidate the interplay of wet and dry extremes at a grid cell scale, we introduce two new metrics: the wet–dry (WD) ratio and the extreme transition (ET) time intervals. The WD ratio measures the relative occurrence of wet or dry extremes, whereas ET quantifies the average separation time of hydrological extremes with opposite signs. The WD ratio shows that the incidence of wet extremes dominates over dry extremes in the USA, northern and southern South America, northern Europe, north Africa, western China, and most of Australia. Conversely, dry extremes are more prominent in most of the remaining regions. The median ET for wet to dry is ∼27 months, while the dry-to-wet median ET is 21 months. We also evaluate correlations between wet–dry hydrological extremes and leading modes of climate variability, namely the El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multi-decadal Oscillation (AMO). We find that ENSO and PDO have a similar influence globally, with the former significantly impacting (p value < 0.05) a larger area (18.1 % of total sc_PDSI_pm area) compared to the latter (12.0 %), whereas the AMO shows an almost inverse pattern and significantly impacts the largest area overall (18.9 %). ENSO and PDO show the most significant correlations over northern South America, the central and western USA, the Middle East, eastern Russia, and eastern Australia. On the other hand, the AMO shows significant associations over Mexico, Brazil, central Africa, the Arabian Peninsula, China, and eastern Russia. Our analysis brings new insights on hydrological multi-hazards that are of relevance to governments and organizations with globally distributed interests. Specifically, the multi-hazard maps may be used to evaluate worst-case disaster scenarios considering the potential co-occurrence of wet and dry hydrological extremes.

scholarly journals Response of flood events to extreme precipitation: two case studies in Taihu Basin, China

2021 ◽  
Author(s):  
Feiqing Jiang ◽  
Zengchuan Dong ◽  
Yun Luo ◽  
Moyang Liu ◽  
Tao Zhou ◽  
...  
Keyword(s):  
Flood Risk ◽  
Extreme Precipitation ◽  
Flood Control ◽  
Return Periods ◽  
Flood Events ◽  
Copula Functions ◽  
Taihu Basin ◽  
Extreme Flood ◽  
Genetic Mechanisms ◽  
Precipitation Events

Abstract Flood events are typically triggered by extreme precipitation in rain-dominant basins. In this study, to better understand the genetic mechanisms and characteristics of floods, copula functions are used to analyze the response of flood events to extreme precipitation. The coincidence probabilities of the typical extreme flood and precipitation events are calculated; different return periods of their arbitrary combinations are calculated, whereas the dangerous domains for flood control under different return periods are identified; furthermore, flood risk analysis under different extreme precipitation scenarios is performed via their conditional exceedance probabilities. The Xitiaoxi catchment (XC) and Dongtiaoxi catchment (DC) in the Zhexi Region of the Taihu Basin are selected as the study area. The results show that in four scenarios with precipitation frequencies of 80%, 90%, 93.33%, and 95%, the probabilities of the dangerous flood are 9.72%, 10.57%, 10.86%, and 11.01% in the XC, respectively, and 5.91%, 6.31%, 6.44%, and 6.51% in the DC, respectively. This study provides a practical basis and guidance for the computation of rainstorm designs, management of flood control safety, and water resource scheduling in the Taihu Basin.

scholarly journals Extensive spatio-temporal assessment of flood events by application of pair-copulas

2015 ◽  
Vol 370 ◽  
pp. 177-181 ◽  
Author(s):  
M. Schulte ◽  
A. H. Schumann
Keyword(s):  
River Basin ◽  
Flood Risk ◽  
Dependence Structure ◽  
Flood Events ◽  
Multivariate Statistical ◽  
Local Conditions ◽  
Extreme Flood ◽  
Multivariate Statistical Approach ◽  
Spatio Temporal ◽  
Peak Discharges

Abstract. Although the consequences of floods are strongly related to their peak discharges, a statistical classification of flood events that only depends on these peaks may not be sufficient for flood risk assessments. In many cases, the flood risk depends on a number of event characteristics. In case of an extreme flood, the whole river basin may be affected instead of a single watershed, and there will be superposition of peak discharges from adjoining catchments. These peaks differ in size and timing according to the spatial distribution of precipitation and watershed-specific processes of flood formation. Thus, the spatial characteristics of flood events should be considered as stochastic processes. Hence, there is a need for a multivariate statistical approach that represents the spatial interdependencies between floods from different watersheds and their coincidences. This paper addresses the question how these spatial interdependencies can be quantified. Each flood event is not only assessed with regard to its local conditions but also according to its spatio-temporal pattern within the river basin. In this paper we characterise the coincidence of floods by trivariate Joe-copula and pair-copulas. Their ability to link the marginal distributions of the variates while maintaining their dependence structure characterizes them as an adequate method. The results indicate that the trivariate copula model is able to represent the multivariate probabilities of the occurrence of simultaneous flood peaks well. It is suggested that the approach of this paper is very useful for the risk-based design of retention basins as it accounts for the complex spatio-temporal interactions of floods.

Impacts of El Niño Southern Oscillation on flood risk and insured losses in New Zealand

2021 ◽  
Author(s):  
Francesco Comola ◽  
Carlotta Scudeler ◽  
Saket Satyam ◽  
Ludovico Nicotina
Keyword(s):  
Time Series ◽  
New Zealand ◽  
Flood Risk ◽  
Southern Oscillation ◽  
Asia Pacific ◽  
Economic Losses ◽  
Flood Events ◽  
Enso Events ◽  
Insured Losses ◽  
Enso Phases

&lt;p&gt;Global warming is expected to enhance El Ni&amp;#241;o Southern Oscillation (ENSO) with potential impacts on rainfall and flood risk in numerous countries of the Asia-Pacific region. Modeling studies have suggested that positive and negative ENSO phases may intensify by as much as 25% under extreme climate projections. However, the influence of ENSO variability on flood risk in Asia-Pacific countries is still largely unexplored. Here, we aim to shed light into the link between ENSO, flood risk, and insured losses in New Zealand by combining rainfall observations and state-of-the-art flood risk models. We draw on 60 years of daily precipitation measurements to quantify the statistical correlations between the rainfall principal components and the ENSO historical time series. This allows us to generate 50,000 years of stochastic daily rainfall maps correlated with a long-term, synthetic ENSO time series. The stochastic precipitation maps are then used to drive streamflow and flood simulations at 20 m spatial resolution. Our results indicate that positive and negative ENSO phases increase the flood risk in different regions of New Zealand, and that extreme ENSO events tend to cause more severe flood events. We finally investigate the potential differences in economic losses during positive and negative ENSO phases by combining modeled flood footprints with exposure and vulnerability data. These results may guide the implementation of effective adaptation and mitigation strategies against the increasing risk of flood events in warming climate.&lt;/p&gt;

scholarly journals Assessment of extreme flood events in a changing climate for a long-term planning of socio-economic infrastructure in the Russian Arctic

2017 ◽  
Vol 21 (5) ◽  
pp. 2559-2578 ◽  
Author(s):  
Elena Shevnina ◽  
Ekaterina Kourzeneva ◽  
Viktor Kovalenko ◽  
Timo Vihma
Keyword(s):  
The Arctic ◽  
Future Climate Change ◽  
Exceedance Probability ◽  
Russian Arctic ◽  
Flood Events ◽  
Spring Flood ◽  
Flood Depth ◽  
Extreme Flood ◽  
Economic Infrastructure

Abstract. Climate warming has been more acute in the Arctic than at lower latitudes and this tendency is expected to continue. This generates major challenges for economic activity in the region. Among other issues is the long-term planning and development of socio-economic infrastructure (dams, bridges, roads, etc.), which require climate-based forecasts of the frequency and magnitude of detrimental flood events. To estimate the cost of the infrastructure and operational risk, a probabilistic form of long-term forecasting is preferable. In this study, a probabilistic model to simulate the parameters of the probability density function (PDF) for multi-year runoff based on a projected climatology is applied to evaluate changes in extreme floods for the territory of the Russian Arctic. The model is validated by cross-comparison of the modelled and empirical PDFs using observations from 23 sites located in northern Russia. The mean values and coefficients of variation (CVs) of the spring flood depth of runoff are evaluated under four climate scenarios, using simulations of six climate models for the period 2010–2039. Regions with substantial expected changes in the means and CVs of spring flood depth of runoff are outlined. For the sites located within such regions, it is suggested to account for the future climate change in calculating the maximal discharges of rare occurrence. An example of engineering calculations for maximal discharges with 1 % exceedance probability is provided for the Nadym River at Nadym.

scholarly journals Mapping and analysis of river network modification as a factor of flood risk in the Blanice river basin

Geografie ◽  
2006 ◽  
Vol 111 (3) ◽  
pp. 274-291
Author(s):  
Jakub Langhammer ◽  
Milada Matoušková
Keyword(s):  
River Basin ◽  
Flood Risk ◽  
Spatial Differentiation ◽  
River Network ◽  
Hydrological Extremes ◽  
Extreme Flood ◽  
Significant Phenomenon ◽  
Analysis Of Results ◽  
Normal Water ◽  
Anthropogenic Modifications

Anthropogenic modifications of river network represent a significant phenomenon that influences runoff conditions in river basins, both under normal water level conditions as well as in the period of hydrological extremes. Modifications of watercourses on various levels influence the speed and timing of floodwave progress as well as the potential to efficiently transform the floodwave in the floodplain and to lessen the extremity of the flood event. The paper presents the methodological framework for analysis of historical and current intensity and nature of man-made modifications of river network. There are presented two essential approaches: First represents the analysis of distance data, e.g. the water management maps, historical maps or aerial imagery. The second approach is based on field mapping of various parameters of river network and floodplain modifications. The presented methodologies are applied on the Blanice river basin that represents the core zone of extreme flood in August 2002 that heavily affected the Central Europe. The GIS analysis of results revealed the spatial differentiation of anthropogenic changes in river basin and their potential importance in the context of the flood risk. The results and the applied methodologies are discussed from the viewpoint of their practical applicability and of limitations in terms of data accuracy, availability and reliability.

scholarly journals Flood Risk and Adaptation Strategies for Soybean Production Systems on the Flood-Prone Pampas under Climate Change

Agronomy ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1187
Author(s):  
Wouter Julius Smolenaars ◽  
Spyridon Paparrizos ◽  
Saskia Werners ◽  
Fulco Ludwig
Keyword(s):  
Climate Change ◽  
Flood Risk ◽  
Risk Perceptions ◽  
Production Systems ◽  
Adaptation Strategies ◽  
Flood Events ◽  
Climate Data ◽  
Soybean Production ◽  
Drying Trend ◽  
Sowing Season

In recent decades, multiple flood events have had a devastating impact on soybean production in Argentina. Recent advances suggest that the frequency and intensity of destructive flood events on the Argentinian Pampas will increase under pressure from climate change. This paper provides bottom-up insight into the flood risk for soybean production systems under climate change and the suitability of adaptation strategies in two of the most flood-prone areas of the Pampas region. The flood risk perceptions of soybean producers were explored through interviews, translated into climatic indicators and then studied using a multi-model climate data analysis. Soybean producers perceived the present flood risk for rural accessibility to be of the highest concern, especially during the harvest and sowing seasons when heavy machinery needs to reach soybean lots. An analysis of climatic change projections found a rising trend in annual and harvest precipitation and a slight drying trend during the sowing season. This indicates that the flood risk for harvest accessibility may increase under climate change. Several adaptation strategies were identified that can systemically address flood risks, but these require collaborative action and cannot be undertaken by individual producers. The results suggest that if cooperative adaptation efforts are not made in the short term, the continued increase in flood risk may force soybean producers in the case study locations to shift away from soybean towards more robust land uses.

scholarly journals Coastal flood risk within a peri-urban area: SUSSEX Inlet district, SE Australia

2021 ◽  
Author(s):  
E. F. Asbridge ◽  
D. Low Choy ◽  
B. Mackey ◽  
S. Serrao-Neumann ◽  
P. Taygfeld ◽  
...  
Keyword(s):  
Flood Risk ◽  
Flood Hazard ◽  
Extreme Rainfall ◽  
Cost Effective ◽  
Extreme Rainfall Events ◽  
Hazard Exposure ◽  
Rate Of Increase ◽  
Eastern Australia ◽  
Planning Strategies ◽  
Natural Resource Managers

AbstractThe peri-urban interface (PUI) exhibits characteristic qualities of both urban and rural regions, and this complexity has meant that risk assessments and long-term planning for PUI are lagging, despite these areas representing new developing settlement frontiers. This study aims to address this knowledge gap by modifying an existing approach to quantify and assess flood risk. The risk triangle framework was used to map exposure, vulnerability and biophysical variables; however, in a novel application, the risk triangle framework was adapted by presuming that there is a variation in the degree of exposure, vulnerability and biophysical variables. Within Australia and globally, PUIs are often coastal, and flood risk associated with rainfall and coastal inundation poses considerable risk to communities in the PUI; these risks will be further exacerbated should projections of increasing frequency of extreme rainfall events and accelerating sea-level rise eventuate. An indicator-based approach using the risk triangle framework that maps flood hazard, exposure and vulnerability was used to integrate the biophysical and socio-economic flooding risk for communities in PUI of the St Georges Basin and Sussex Inlet catchments of south-eastern Australia. Integrating the flood risk triangle with future scenarios of demographic and climate change, and considering factors that contribute to PUI flood risk, facilitated the identification of planning strategies that would reduce the future rate of increase in flood risk. These planning strategies are useful for natural resource managers and land use planners across Australia and globally, who are tasked with balancing socio-economic prosperity for a changing population, whilst maintaining and enhancing ecosystem services and values. The indicator-based approach used in this study provides a cost-effective first-pass risk assessment and is a valuable tool for decision makers planning for flood risk across PUIs in NSW and globally.

scholarly journals Ectomycorrhiza resilience and recovery to extreme flood events in Tuber aestivum and Quercus robur

Mycorrhiza ◽  
2021 ◽  
Author(s):  
P. W. Thomas
Keyword(s):  
Climate Change ◽  
Seedling Growth ◽  
Quercus Robur ◽  
Root Systems ◽  
Fruiting Bodies ◽  
Flood Events ◽  
Tuber Aestivum ◽  
Soil Zone ◽  
Extreme Flood ◽  
The Impact

AbstractVery little is known about the impact of flooding and ground saturation on ectomycorrhizal fungi (EcM) and increasing flood events are expected with predicted climate change. To explore this, seedlings inoculated with the EcM species Tuber aestivum were exposed to a range of flood durations. Oak seedlings inoculated with T. aestivum were submerged for between 7 and 65 days. After a minimum of 114-day recovery, seedling growth measurements were recorded, and root systems were destructively sampled to measure the number of existing mycorrhizae in different zones. Number of mycorrhizae did not display correlation with seedling growth measurements. Seven days of submersion resulted in a significant reduction in mycorrhizae numbers and numbers reduced most drastically in the upper zones. Increases in duration of submersion further impacted mycorrhizae numbers in the lowest soil zone only. T. aestivum mycorrhizae can survive flood durations of at least 65 days. After flooding, mycorrhizae occur in higher numbers in the lowest soil zone, suggesting a mix of resilience and recovery. The results will aid in furthering our understanding of EcM but also may aid in conservation initiatives as well as providing insight for those whose livelihoods revolve around the collection of EcM fruiting bodies or cropping of the plant partners.

scholarly journals The FLOod Probability Interpolation Tool (FLOPIT): A Simple Tool to Improve Spatial Flood Probability Quantification and Communication

Water ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 666
Author(s):  
Mahkameh Zarekarizi ◽  
K. Joel Roop-Eckart ◽  
Sanjib Sharma ◽  
Klaus Keller
Keyword(s):  
Flood Risk ◽  
Water Surface ◽  
The United States ◽  
Surface Elevation ◽  
Exceedance Probability ◽  
Water Surface Elevation ◽  
Inundation Maps ◽  
Probability Maps ◽  
Flood Probability ◽  
Floodplain Development

Understanding flood probabilities is essential to making sound decisions about flood-risk management. Many people rely on flood probability maps to inform decisions about purchasing flood insurance, buying or selling real-estate, flood-proofing a house, or managing floodplain development. Current flood probability maps typically use flood zones (for example the 1 in 100 or 1 in 500-year flood zones) to communicate flooding probabilities. However, this choice of communication format can miss important details and lead to biased risk assessments. Here we develop, test, and demonstrate the FLOod Probability Interpolation Tool (FLOPIT). FLOPIT interpolates flood probabilities between water surface elevation to produce continuous flood-probability maps. FLOPIT uses water surface elevation inundation maps for at least two return periods and creates Annual Exceedance Probability (AEP) as well as inundation maps for new return levels. Potential advantages of FLOPIT include being open-source, relatively easy to implement, capable of creating inundation maps from agencies other than FEMA, and applicable to locations where FEMA published flood inundation maps but not flood probability. Using publicly available data from the Federal Emergency Management Agency (FEMA) flood risk databases as well as state and national datasets, we produce continuous flood-probability maps at three example locations in the United States: Houston (TX), Muncy (PA), and Selinsgrove (PA). We find that the discrete flood zones generally communicate substantially lower flood probabilities than the continuous estimates.

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