Defining Flood Zone Transitions in Low‐Gradient Coastal Regions

Bilskie, Matthew V.; Hagen, Scott C.

doi:10.1002/2018gl077524

Cited by 118 publications

(104 citation statements)

References 33 publications

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“…Second, even in the presence of synoptic weather systems, this does not ensure a strong and positive dependence between storm surge and discharge. Drivers of maximum storm surge heights are particularly complex, and are influenced by external factors such as local bathymetry and the geometry of the coastline (Bloemendaal et al, 2019). Third, in large catchments, there may also be a lag of several days for river flood waves to reach the basin outlet (Allen et al, 2018), such that the riverine and coastal flood annual maxima do not interact (Kew et al, 2013;Klerk et al, 2015;Ward et al, 2018).…”

Section: Quantification Of the Compound Flood Hazard Potentialmentioning

confidence: 99%

Measuring compound flood potential from river discharge and storm surge extremes at the global scale

Couasnon

Eilander

Muis

et al. 2020

Nat. Hazards Earth Syst. Sci.

170

144

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Abstract. The interaction between physical drivers from oceanographic, hydrological, and meteorological processes in coastal areas can result in compound flooding. Compound flood events, like Cyclone Idai and Hurricane Harvey, have revealed the devastating consequences of the co-occurrence of coastal and river floods. A number of studies have recently investigated the likelihood of compound flooding at the continental scale based on simulated variables of flood drivers, such as storm surge, precipitation, and river discharges. At the global scale, this has only been performed based on observations, thereby excluding a large extent of the global coastline. The purpose of this study is to fill this gap and identify regions with a high compound flooding potential from river discharge and storm surge extremes in river mouths globally. To do so, we use daily time series of river discharge and storm surge from state-of-the-art global models driven with consistent meteorological forcing from reanalysis datasets. We measure the compound flood potential by analysing both variables with respect to their timing, joint statistical dependence, and joint return period. Our analysis indicates many regions that deviate from statistical independence and could not be identified in previous global studies based on observations alone, such as Madagascar, northern Morocco, Vietnam, and Taiwan. We report possible causal mechanisms for the observed spatial patterns based on existing literature. Finally, we provide preliminary insights on the implications of the bivariate dependence behaviour on the flood hazard characterisation using Madagascar as a case study. Our global and local analyses show that the dependence structure between flood drivers can be complex and can significantly impact the joint probability of discharge and storm surge extremes. These emphasise the need to refine global flood risk assessments and emergency planning to account for these potential interactions.

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Section: Quantification Of the Compound Flood Hazard Potentialmentioning

confidence: 99%

Measuring compound flood potential from river discharge and storm surge extremes at the global scale

Couasnon

Eilander

Muis

et al. 2020

Nat. Hazards Earth Syst. Sci.

170

144

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“…While most of the 1% recurrence events occur when wave heights are greater than 5 m and wave periods longer than 15 s, there is an infinite combination of univariate drivers that can combine to generate compound extreme events—even for a simple TWL proxy such as equation . Such different TWL components can lead to different impacts on the open beach (Cohn et al, ; Serafin et al, ; Serafin et al, ) and different flood extents in the backshore (Bilskie & Hagen, ). The presented framework can be a tool used to make informed decisions for the input conditions to dynamical numerical modeling studies assessing flood extents and hazard zones contingent on future extremes (Barnard et al, ; Erikson et al, ).…”

Section: Climate Emulator Twl Outputmentioning

confidence: 99%

Time‐Varying Emulator for Short and Long‐Term Analysis of Coastal Flood Hazard Potential

et al. 2019

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Rising seas coupled with ever increasing coastal populations present the potential for significant social and economic loss in the 21st century. Relatively short records of the full multidimensional space contributing to total water level coastal flooding events (astronomic tides, sea level anomalies, storm surges, wave run-up, etc.) result in historical observations of only a small fraction of the possible range of conditions that could produce severe flooding. The Time-varying Emulator for Short-and Long-Term analysis of coastal flood hazard potential is presented here as a methodology capable of producing new iterations of the sea-state parameters associated with the present-day Pacific Ocean climate to simulate many synthetic extreme compound events. The emulator utilizes weather typing of fundamental climate drivers (sea surface temperatures, sea level pressures, etc.) to reduce complexity and produces new daily synoptic weather chronologies with an auto-regressive logistic model accounting for conditional dependencies on the El Niño Southern Oscillation, the Madden-Julian Oscillation, seasonality, and the prior two days of weather progression. Joint probabilities of sea-state parameters unique to simulated weather patterns are used to create new time series of the hypothetical components contributing to synthetic total water levels (swells from multiple directions coupled with water levels due to wind setup, temperature anomalies, and tides). The Time-varying Emulator for Short-and Long-Term analysis of coastal flood hazard potential reveals the importance of considering the multivariate nature of extreme coastal flooding, while progressing the ability to incorporate large-scale climate variability into site specific studies assessing hazards within the context of predicted climate change in the 21st century.Plain Language Summary Predicting extreme coastal flooding is a present-day societal need and will only become more relevant as mean water levels increase due to sea level rise. However, the number of processes contributing to such events is too high for relatively short observational records to have measured all of the constructive combinations of waves, surge, wind, and sea level anomalies. We present a framework designed to create hypothetical combinations of relevant flood hazard potential processes by simulating the climate and weather patterns that drive coastal flooding. Including large-scale oceanic and atmospheric patterns as the drivers of coastal hazards reveals the climate a coastal community is most vulnerable to, which will be increasingly more important to understand as the climate changes during the 21st century.

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“…When two or more of these mechanisms occur simultaneously, flood severity may be exacerbated leading to increased coastal flood risk. Examples of compound flood events include the combination of river discharge and surges (Moftakhari et al, ; Ward et al, ), rainfall and surges (Wahl et al, , in the U.S. coasts and Wu et al, , in Australia), and rainfall, surge, and waves (Bilskie & Hagen, ; Paprotny et al, ). If these concurrent events display statistical dependencies (e.g., through a common forcing mechanism), the probability of their joint occurrence (i.e., the chance of two or more extreme conditions occurring at the same time) is higher than that expected considering separately the extremes of each variable, with a consequent increase of the likelihood of coastal flooding.…”

Section: Introductionmentioning

confidence: 99%

Increased Extreme Coastal Water Levels Due to the Combined Action of Storm Surges and Wind Waves

Marcos

Rohmer

Vousdoukas

et al. 2019

Geophysical Research Letters

109

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The dependence between extreme storm surges and wind waves is assessed statistically along the global coasts using the outputs of two numerical models consistently forced with the same atmospheric fields. We show that 55% of the world coastlines face compound storm surge wave extremes. Hence, for a given level of probability, neglecting these dependencies leads to underestimating extreme coastal water levels. Dependencies are dominant in midlatitudes and are likely underestimated in the tropics due to limited representation of tropical cyclones. Furthermore, we show that in half of the areas with dependence, the estimated probability of occurrence of coastal extreme water levels increases significantly when it is accounted for. Translated in terms of return periods, this means that along 30% of global coastlines, extreme water levels expected at most once in a century without considering dependence between storm surges and waves become a 1 in 50‐year event.

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Defining Flood Zone Transitions in Low‐Gradient Coastal Regions

Cited by 118 publications

References 33 publications

Measuring compound flood potential from river discharge and storm surge extremes at the global scale

Measuring compound flood potential from river discharge and storm surge extremes at the global scale

Time‐Varying Emulator for Short and Long‐Term Analysis of Coastal Flood Hazard Potential

Increased Extreme Coastal Water Levels Due to the Combined Action of Storm Surges and Wind Waves

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