Storm Surge Height Research Articles

A review on impact of typhoons and hurricanes on coastal wetland ecosystems

Tropical storms (typhoons and hurricanes) are an important form of natural disturbance in coastal wetland ecosystems in tropical and temperate regions. The impacts of a tropical storm on coastal wetland ecosystems are diverse and complex, and their influence on the structure, process, and function of coastal wetland ecosystems and landscape changes has been studied extensively. This paper reviews the effects of typhoons and hurricanes on coastal wetland plants and animals, carbon and nitrogen cycles, water quality, sediments, wetland landscape changes, and recovery. Direct and indirect impacts of typhoons and hurricanes are analyzed mainly from their paths and characteristics, and the response of coastal wetland ecosystems. Typhoons and hurricanes cause damage to mangroves, including the loss of foliage, broken trunks, and even uprooting. The damage varies based on the tree species, stand structure, location, and intensity of the typhoon, or hurricane. Typhoons and hurricanes also affect large aquatic plants and phytoplankton, such as seagrass and algae, including their community structure and species richness. The numbers of coastal wetland animals and their species diversity decrease because of the damage and change of habitat following a disturbance. However, some coastal wetland animals in the disturbance-prone ecosystems demonstrate adaptability to the disturbance, such as high dispersal ability, to cope with partial or total loss of local populations and habitats. Saltwater intrusion induced by tropical storm causes obvious impacts on the production and emission of CH4 and CO2. The short- and long-term changes of wetland water quality are influenced by the concomitant heavy rains. Storm surges transport sandy and muddy littoral and shallow offshore sediments hundreds to thousands of meters inland, and represent an important pathway for sediment delivery into the interior of coastal marshes. Sediment transported by hurricanes is one of the important sources of coastal wetland sediment deposition. Their volume, physical properties (bulk density and grain size), and the material they contain vary with the different distances to the shoreline and the storm path. Typhoons and hurricanes cause coastal erosion by induced storm surges and the decrease of wetland area, and changes to wetland morphology and elevation. These acute effects may reduce the future ability of coastal wetlands to protect landward areas from the impacts of storms by dampening wave energy, distancing the mainland from the open water, and potentially reducing the storm surge height. The long-term impacts and recovery of damaged coastal wetlands depend on the intensity and frequency of typhoons and hurricanes. The recovery speeds of tidal creeks and vegetated wetlands are different, as are those of the different tree species. During the recovery process, plant and animal communities interact with each other. Finally, our review clarifies the current knowledge gap in this research, and helps give direction for future research that is still needed.

Extreme sea levels under present and future climate: a pan-European database

Continental or global studies of coastal flood hazard in the context of climate change encounter several obstacles. The primary concern is the limited coverage of sea level data, especially the high-frequency sort needed to analyse sea level extremes. In this paper we present the calculations of return periods of storm surge heights and water levels for the European coast. The analysis utilized simulations using Delft3D hydrodynamic model driven by meteorological data with temporal and spatial resolution, created under EURO-CORDEX activities. The simulations were calibrated using short- and long-term sea levels from over 150 gauges. Annual maxima of water levels were extracted from five simulations: 1971–2000 historical run as well as 2021–50 and 2071–2100 simulations based on two emissions scenarios each. Spatially varying sea level rise projections were also included. Annual maxima were then fitted to probability distributions in order to obtain the return periods. The results were combined with more than 70,000 coastal sections, so that they would be complimentary with a river flood hazard dataset developed in parallel. The study showed a good match between simulated and observed storm surge heights. It also shows large differences in future trends of water levels in Europe.

Spatial variability in the trends in extreme storm surges and weekly-scale high water levels in the eastern Baltic Sea

We address the possibilities of a separation of the overall increasing trend in maximum water levels of semi-enclosed water bodies into associated trends in the heights of local storm surges and basin-scale components of the water level based on recorded and modelled local water level time series. The test area is the Baltic Sea. Sequences of strong storms may substantially increase its water volume and raise the average sea level by almost 1m for a few weeks. Such events are singled out from the water level time series using a weekly-scale average. The trends in the annual maxima of the weekly average have an almost constant value along the entire eastern Baltic Sea coast for averaging intervals longer than 4 days. Their slopes are ~4cm/decade for 8-day running average and decrease with an increase of the averaging interval. The trends for maxima of local storm surge heights represent almost the entire spatial variability in the water level maxima. Their slopes vary from almost zero for the open Baltic Proper coast up to 5–7cm/decade in the eastern Gulf of Finland and Gulf of Riga. This pattern suggests that an increase in wind speed in strong storms is unlikely in this area but storm duration may have increased and wind direction may have rotated.

Modeling the interaction between tides and storm surges for the Taiwan coast

An unstructured grid, two-dimensional hydrodynamic model was established and applied to the coast of Taiwan to investigate the tide-surge interaction. Tidal elevations at the open boundaries coupled with a global ocean tidal model and the meteorological conditions using a cyclone model are used to drive the model. The model was calibrated and verified with the observed tidal levels at six tidal stations for seven typhoon events to ascertain the capability and feasibility of the model. The results show reasonable agreement between the simulated and observed tidal levels. The validated model was then applied to probe the influence of tide-surge interaction on phase, water levels, and storm surge height. We found that the tide-surge interaction influenced both the magnitude and timing of the surge, which depended on the typhoon path. The storm surge heights at different tidal stations were significantly influenced by wind stresses and directions. The water level rise due to the storm surge during high tide was greater at neap tide than at spring tide. Changing tidal ranges altered the prediction of the surge enough to induce the changes in peak water levels.

Coastal Flood Assessment Based on Field Debris Measurements and Wave Runup Empirical Model

On 6 December 2010, an extra-tropical storm reached Atlantic Canada, causing coastal flooding due to high water levels being driven toward the north shore of Chaleur Bay. The extent of flooding was identified in the field along the coastline at Maria using DGPS. Using the assumption that the maximum elevation of flooded areas represents the combination of astronomical tide, storm surge and wave runup, which is the maximum elevation reached by the breaking waves on the beach, all flood limits were identified. A flood-zone delineation was performed using GIS and LiDAR data. An empirical formula was used to estimate runup elevation during the flood event. A coastal flood map of the 6 December flood event was made using empirical data and runup calculations according to offshore wave climate simulations. Along the natural beach, results show that estimating runup based on offshore wave data and upper foreshore beach slope represents well the observed flood extent. Where a seawall occupies the beach, wave breaking occurs at the toe of the structure and wave height needs to be considered independently of runup. In both cases (artificial and natural), flood risk is underestimated if storm surge height alone is considered. There is a need to incorporate wave characteristics in order to adequately model potential flood extent. A coastal flooding projection is proposed for Pointe Verte based on total water levels estimated according to wave climate simulation return periods and relative sea-level rise for the Chaleur Bay.

Identification of storm surge vulnerable areas in the Philippines through the simulation of Typhoon Haiyan-induced storm surge levels over historical storm tracks

Abstract. Super Typhoon Haiyan entered the Philippine Area of Responsibility (PAR) on 7 November 2013, causing tremendous damage to infrastructure and loss of lives mainly due to the storm surge and strong winds. Storm surges up to a height of 7 m were reported in the hardest hit areas. The threat imposed by this kind of natural calamity compelled researchers of the Nationwide Operational Assessment of Hazards (Project NOAH) which is the flagship disaster mitigation program of the Department of Science and Technology (DOST) of the Philippine government to undertake a study to determine the vulnerability of all Philippine coastal communities to storm surges of the same magnitude as those generated by Haiyan. This study calculates the maximum probable storm surge height for every coastal locality by running simulations of Haiyan-type conditions but with tracks of tropical cyclones that entered PAR from 1948–2013. One product of this study is a list of the 30 most vulnerable coastal areas that can be used as a basis for choosing priority sites for further studies to implement appropriate site-specific solutions for flood risk management. Another product is the storm tide inundation maps that the local government units can use to develop a risk-sensitive land use plan for identifying appropriate areas to build residential buildings, evacuation sites, and other critical facilities and lifelines. The maps can also be used to develop a disaster response plan and evacuation scheme.

Identification of storm surge events over the German Bight from atmospheric reanalysis and climate model data

Abstract. A new procedure for the identification of storm surge situations for the German Bight is developed and applied to reanalysis and global climate model data. This method is based on the empirical approach for estimating storm surge heights using information about wind speed and wind direction. Here, we hypothesize that storm surge events are caused by high wind speeds from north-westerly direction in combination with a large-scale wind storm event affecting the North Sea region. The method is calibrated for ERA-40 data, using the data from the storm surge atlas for Cuxhaven. It is shown that using information of both wind speed and direction as well as large-scale wind storm events improves the identification of storm surge events. To estimate possible future changes of potential storm surge events, we apply the new identification approach to an ensemble of three transient climate change simulations performed with the ECHAM5/MPIOM model under A1B greenhouse gas scenario forcing. We find an increase in the total number of potential storm surge events of about 12 % [(2001–2100)–(1901–2000)], mainly based on changes of moderate events. Yearly numbers of storm surge relevant events show high interannual and decadal variability and only one of three simulations shows a statistical significant increase in the yearly number of potential storm surge events between 1900 and 2100. However, no changes in the maximum intensity and duration of all potential events is determined. Extreme value statistic analysis confirms no frequency change of the most severe events.

Climate change effects on the worst-case storm surge: a case study of Typhoon Haiyan

Effects of climate change on the worst case scenario of a storm surge induced by a super typhoon in the present climate are investigated through the case study of Typhoon Haiyan. We present the results of our investigation on super-typhoon Haiyan by using a super high resolution (1 km grid) regional model that explicitly handles cloud microphysical processes. As the parent model, we adopted the operational weekly ensemble experiments (60 km grid) of the Japan Meteorological Agency, and compared experiments using sea surface temperatures and atmospheric environmental parameters from before the beginning of anthropogenic climate change (150 years ago) with those using observed values throughout the typhoon. We were able not only to represent the typhoon’s intensity but also to evaluate the influences of climate change on worst case storm surges in the Gulf of Leyte due to a typhoon with high robustness. In 15 of 16 ensemble experiments, the intensity of the simulated worst case storm in the actual conditions was stronger than that in a hypothetical natural condition without historical anthropogenic forcing during the past 150 years. The intensity of the typhoon is translated to a disaster metric by simulating the storm surge height by using a shallow-water long-wave model. The result indicates that the worst case scenario of a storm surge in the Gulf of Leyte may be worse by 20%, though changes in frequency of such events are not accounted for here.

Extreme storm surge hazard estimation in lower Manhattan

The coastal destruction wreaked by Hurricane Sandy in 2012 prompted motivation to estimate the event’s return period. The Clustered Separated Peaks-over-threshold Simulation (CSPS) method for estimating return periods uses a Monte Carlo simulation of storm surge activity based on statistics derived from tidal gauge data at the Battery, New York in lower Manhattan. The data are separated into three independent components (storm surge, tidal cycle and sea level rise) because different physical processes govern different components of water level. Peak storm surge heights are fit to the generalized Pareto distribution, chosen for its ability to fit a wide tail to limited data. The algorithm incorporates the evolution of storm surge over surge duration. The CSPS suggests that the return period of Hurricane Sandy’s peak water level is 103 years (95% confidence interval 38–452 years), significantly lower than previously published return periods. The estimated 100-year water level is 5.23 m above the station datum (or 3.39 m above the North American Vertical Datum of 1988, or 3.45 m above mean sea level). With 1 m of sea level rise (holding all other climatological conditions constant), this water level would become the 28-year event. Although the method’s exclusion of surge-tide interaction and its reliance on a 90-year tidal gauge time history may limit the reliability of high return period estimates, application of the CSPS method to lower Manhattan suggests that storm surge hazard in the New York Harbor has, until now, been underestimated.

Probabilistic storm surge inundation maps for Metro Manila based on Philippine public storm warning signals

Abstract. A storm surge is the sudden rise of sea water over the astronomical tides, generated by an approaching storm. This event poses a major threat to the Philippine coastal areas, as manifested by Typhoon Haiyan on 8 November 2013. This hydro-meteorological hazard is one of the main reasons for the high number of casualties due to the typhoon, with 6300 deaths. It became evident that the need to develop a storm surge inundation map is of utmost importance. To develop these maps, the Nationwide Operational Assessment of Hazards under the Department of Science and Technology (DOST-Project NOAH) simulated historical tropical cyclones that entered the Philippine Area of Responsibility. The Japan Meteorological Agency storm surge model was used to simulate storm surge heights. The frequency distribution of the maximum storm surge heights was calculated using simulation results of tropical cyclones under a specific public storm warning signal (PSWS) that passed through a particular coastal area. This determines the storm surge height corresponding to a given probability of occurrence. The storm surge heights from the model were added to the maximum astronomical tide data from WXTide software. The team then created maps of inundation for a specific PSWS using the probability of exceedance derived from the frequency distribution. Buildings and other structures were assigned a probability of exceedance depending on their occupancy category, i.e., 1% probability of exceedance for critical facilities, 10% probability of exceedance for special occupancy structures, and 25% for standard occupancy and miscellaneous structures. The maps produced show the storm-surge-vulnerable areas in Metro Manila, illustrated by the flood depth of up to 4 m and extent of up to 6.5 km from the coastline. This information can help local government units in developing early warning systems, disaster preparedness and mitigation plans, vulnerability assessments, risk-sensitive land use plans, shoreline defense efforts, and coastal protection measures. These maps can also determine the best areas to build critical structures, or at least determine the level of protection of these structures should they be built in hazard areas. Moreover, these will support the local government units' mandate to raise public awareness, disseminate information about storm surge hazards, and implement appropriate countermeasures for a given PSWS.

Coupled storm surge and wave simulations for the Southern Coast of Korea

An integrated model system was developed to apply surge-wave coupled simulations to the southern coast of Korea during Typhoon Sanba in 2012. Numerical experiments were carried out to examine the effects of land-dissipated wind on storm surges and the influence of wave-surge coupled simulations on storm surges and surface waves. These numerical experiments used a finite volume ocean model, FVCOM, coupled with a wave model SWAVE. Due to the complex geometry of the coastal area investigated, a high-resolution terrain-following unstructured grid was employed. Atmospheric forcing was generated by a planetary boundary layer model, which was revised by incorporating the effect of the land’s roughness on the typhoon wind. A detailed comparison shows generally good agreement between the measured and simulated wind, surge, and waves. In particular, improved results have been found for the simulation of storm winds and surges when considering the effect of land-dissipated wind. In addition, clearly improved results for storm surges were obtained when adding the coupling effect between waves and surges. The results show a maximum contribution of ~40% by the waveinduced surge to the peak surge height along the coasts. The mean rate of error for peak surge heights decreased from 29.6% to 21.3% after considering the effects of wind dissipation, and decreased again to 17.9% when adding the effects of the waves. These results imply that the effect of wind dissipation caused by land roughness and waves should be taken into account when determining storm surge heights. The results also show the effects of wave-current coupling influences the generation of waves. However, the magnitude of this coupling effect on wave heights was found to be relatively insignificant.

Statistical Assessment of Storm Surge Scenarios Within Integrated Risk Analyses

This paper summarizes the results from calculating exceedance probabilities of different storm surge scenarios developed within the XtremRisK project, which were then used as boundary conditions for integrated risk analyses for the city of Hamburg in the Elbe Estuary and Sylt Island off the coastline of Schleswig-Holstein in northern Germany. A stochastic storm surge model is developed to simulate a large number of synthetic and physically consistent storm surge scenarios, before the resulting samples are used to calculate bivariate joint exceedance probabilities of the storm surge heights (total water levels with tides included) and intensities. The Copula theory is exploited and functions from the Archimedean family are used to build the statistical models. The latter are extended to the three-dimensional case to also take into account wave conditions where appropriate. The uncertainties associated with the results from the multivariate extreme value analyses are briefly discussed and (where possible) quantified and recommendations of how to exploit the presented methodologies in future applications are given.

A study on simulation of flood inundation in a coastal urban area using a two-dimensional well-balanced finite volume model

In this study, the simulation and analysis of the inundation in a coastal urban area according to the storm surge height are carried out using a two-dimensional finite-volume model with a well-balanced scheme. The target coastal urban area considered in this study is a part of the new town of Changwon city, Gyeongnam province, South Korea; this area was extremely damaged by the storm surge generated during the period of Typhoon Maemi in September 2003. For the purpose of the verification of the numerical model applied in this study, the simulated results are compared and analyzed with the temporal storm surge heights observed at the tide station in Masan Bay and inundation traces in an urban area. Moreover, in order to investigate the influence of super-typhoons possible in the future, the results simulated with the storm surge heights, which were 1.25 and 1.5 times higher than those observed during the period of Typhoon Maemi, are compared and analyzed.

BASIC STUDY ON ESTIMATION METHOD OF RETURN PERIOD AND VARIATION RANGE OF SEVERE STORM SURGE EVENT

Probability risk assessment of storm surge is difficult because the number of historical data of tropical cyclone is not enough for region. Most hazard maps for storm surge were designed based on the assumption that intense tropical cyclone approached in target area. However, its return period and variation range of storm surge have not been considered carefully so much. In this study, we examined them by using stochastic tropical cyclone model and physical storm surge model. Target area was Yatsushiro bay in west Kyshu Island in Japan. From physical storm surge height caused by 300 causes, we decided the severe storm surge scenario and the variation range of maximum storm surge height caused by change of translation speed and radius of tropical cyclone. Finally, by using stochastic tropical cyclone model, the return period of severe storm surge event was estimated about 370 year.

Storminess interannual variability and coastal hazards over the south-western Spanish coast: links to large scale atmospheric forcing

In the context of increased coastal hazards through storminess variability, the danger of coastal damages and/or morphological changes is related to the sum of mean sea level conditions, storm surge and maximum wave height and run up values. In order to better understand the physical processes that cause the interannual variability of the above parameters a reanalysis record (HIPOCAS) of the last 44 years was used. The HIPOCAS time-series was validated with real wind, wave and sea-level data using linear and vector correlation methods. In the present work changes in the duration, frequency, chronology and approach direction of the Atlantic storms over the Spanish Gulf of Cadiz (SW Iberian Peninsula) were identified by computing various storm characteristics such as maximum wave height, total energy per storm and storm groupiness. The obtained time-series were compared with large-scale atmospheric indices such as the North Atlantic Oscillation (NAO) and the East Atlantic pattern (EA). The results show a good correlation between negative NAO values and increased storminess over the entire Gulf of Cadiz. Furthermore, negative NAO values were correlated with high mean sea level values and westerly and south-westerly wind events, indicating higher probability of coastal risks. The above results were compared with coastal inundation events that took place over the last winter seasons in the province of Cadiz.

Sources of 21st century regional sea-level rise along the coast of northwest Europe

Abstract. Changes in both global and regional mean sea level, and changes in the magnitude of extreme flood heights, are the result of a combination of several distinct contributions most, but not all, of which are associated with climate change. These contributions include effects in the solid earth, gravity field, changes in ocean mass due to ice loss from ice sheets and glaciers, thermal expansion, alterations in ocean circulation driven by climate change and changing freshwater fluxes, and the intensity of storm surges. Due to the diverse range of models required to simulate these systems, the contributions to sea-level change have usually been discussed in isolation rather than in one self-consistent assessment. Focusing on the coastline of northwest Europe, we consider all the processes mentioned above and their relative impact on 21st century regional mean sea levels and the 50-year return flood height. As far as possible our projections of change are derived from process-based models forced by the A1B emissions scenario to provide a self-consistent comparison of the contributions. We address uncertainty by considering both a mid-range and an illustrative high-end combination of the different components. For our mid-range ice loss scenario we find that thermal expansion of seawater is the dominant contributor to change in northwest European sea level by 2100. However, the projected contribution to extreme sea level, due to changes in storminess alone, is in some places significant and comparable to the global mean contribution of thermal expansion. For example, under the A1B emissions scenario, by 2100, change in storminess contributes around 15 cm to the increase in projected height of the 50-year storm surge on the west coast of the Jutland Peninsula, compared with a contribution of around 22 cm due to thermal expansion and a total of 58 cm from all of the contributions we consider. An illustrative combination of our high-end projections suggests increases in the 50-year return level of 86 cm at Sheerness, 95 cm at Roscoff, 106 cm at Esbjerg, and 67cm at Bergen. The notable regional differences between these locations arise primarily from differences in the rates of vertical land movement and changes in storminess.

A new catalogue of tropical cyclones of the northern Bay of Bengal and the distribution and effects of selected landfalling events in Bangladesh

ABSTRACTTropical cyclones devastate large areas, take numerous lives and damage extensive property in Bangladesh. Research on landfalling tropical cyclones affecting Bangladesh has primarily focused on events occurring since AD 1960 with limited work examining earlier historical records. We rectify this gap by developing a new tropical cyclone catalogue that maximizes the use of available sources. The catalogue consists of 304 tropical cyclones that occurred between AD 1000 and AD 2009 and made landfall along the coasts of Bangladesh, eastern India and Myanmar. One hundred and ninety‐three events directly struck Bangladesh between AD 1484 and AD 2009, although the precise landfall location of six events is unknown. Of the remaining 187 events, Cox's Bazar, Chittagong, Noakhali, Barisal and Khulna were struck by 30, 46, 19, 41 and 51 tropical cyclones, respectively. There is a paucity of data about tropical cyclones before AD 1900 and this increases the further back in time we go. Inconsistencies in reported storm surge height, wind speed and exaggerations in the reporting of deaths are identified and discussed. Some 20 72 509 human deaths in Bangladesh are associated with 71 tropical cyclones that occurred between AD 1484 and AD 2009. Between AD 1923 and AD 2009, 11 tropical cyclones caused 94 35 000 people to become homeless and between AD 1961 and AD 2009, 10 tropical cyclones resulted in economic damage of over US$ 4.6 billion. Analysis of the deaths and damage associated with tropical cyclones in AD 1970, AD 1991 and AD 2007 indicates that while the number of deaths decreased between events, economic damage and the number of people made homeless increased. There are positive and significant correlations between increasing storm surge height and increasing human fatalities (r = 0.60, p < 0.01) and increasing human injuries and greater wind speed (r = 0.45, p < 0.01). Despite our best efforts, the catalogue is incomplete. As such, we suggest further ‘deep’ archival research coupled with regional geological studies of palaeostorm events to gain a more sophisticated understanding of the hazard. Our results have implications for both risk assessment and disaster risk reduction.

Correlating Storm Surge Heights with Tropical Cyclone Winds at and before Landfall

Abstract This paper investigates relationships between storm surge heights and tropical cyclone wind speeds at 3-h increments preceding landfall. A unique dataset containing hourly tropical cyclone position and wind speed is used in conjunction with a comprehensive storm surge dataset that provides maximum water levels for 189 surge events along the U.S. Gulf Coast from 1880 to 2011. A landfall/surge classification was developed for analyzing the relationship between surge magnitudes and prelandfall winds. Ten of the landfall/surge event types provided useable data, producing 117 wind–surge events that were incorporated into this study. Statistical analysis indicates that storm surge heights correlate better with prelandfall tropical cyclone winds than with wind speeds at landfall. Wind speeds 18 h before landfall correlated best with surge heights. Raising wind speeds to exponential powers produced the best wind–surge fit. Higher wind–surge correlations were found when testing a more recent sample of data that contained 63 wind–surge events since 1960. The highest correlation for these data was found when wind speeds 18 h before landfall were raised to a power of 2.2, which provided R2 values that approached 0.70. The R2 values at landfall for these same data were only 0.44. Such results will be useful to storm surge modelers, coastal scientists, and emergency management personnel, especially when tropical cyclones rapidly strengthen or weaken while approaching the coast.

An Empirical Analysis on the Relationship between Tropical Cyclone Size and Storm Surge Heights along the U.S. Gulf Coast

AbstractIn the past decade, several large tropical cyclones have generated catastrophic storm surges along the U.S. Gulf and Atlantic Coasts. These storms include Hurricanes Katrina, Ike, Isaac, and Sandy. This study uses empirical analysis of tropical cyclone data and maximum storm surge observations to investigate the role of tropical cyclone size in storm surge generation. Storm surge data are provided by the Storm Surge Database (SURGEDAT), a global storm surge database, while a unique tropical cyclone size dataset built from nine different data sources provides the size of the radius of maximum winds (Rmax) and the radii of 63 (34 kt), 93 (50 kt), and 119 km h−1 (64 kt) winds. Statistical analysis reveals an inverse correlation between storm surge magnitudes and Rmax sizes, while positive correlations exist between storm surge heights and the radius of 63 (34 kt), 93 (50 kt), and 119 km h−1 (64 kt) winds. Storm surge heights correlate best with the prelandfall radius of 93 km h−1 (50 kt) winds, with a Spearman correlation coefficient value of 0.82, significant at the 99.9% confidence level. Many historical examples support these statistical results. For example, the 1900 Galveston hurricane, the 1935 Labor Day hurricane, and Hurricane Camille all had small Rmax sizes but generated catastrophic surges. Hurricane Katrina provides an example of the importance of large wind fields, as hurricane-force winds extending 167 km [90 nautical miles (n mi)] from the center of circulation enabled this large storm to generate a higher storm surge level than Hurricane Camille along the same stretch of coast, even though Camille’s prelandfall winds were slightly stronger than Katrina’s. These results may be useful to the storm surge modeling community, as well as disaster science and emergency management professionals, who will benefit from better understanding the role of tropical cyclone size for storm surge generation.

Bay of Bengal cyclone extreme water level estimate uncertainty

Accurate estimates of storm surge magnitude and frequency are essential to coastal flood risk studies. Much research has focused on tide–surge interaction and joint probability techniques to combine multiple cyclone characteristics. In the Bay of Bengal, extreme water levels are derived from numerical storm surge models based on an idealised cyclone event; however, uncertainty within such calculations for this region is poorly understood, especially when propagated through to the flood hazard. We use the IBTrACs data set to estimate natural variability in four key parameters used to describe an idealised cyclone and create a set of idealised but equally likely “1 in 50 year” recurrence interval cyclone events. Each idealised cyclone is then used to force a storm surge model to give predicted peak water levels along the northern Bay of Bengal coast. Finally, extreme water level uncertainty is propagated through an inundation model to predict flood extent and depth over inland coastal floodplains. The descriptive parameters of 18 cyclone events (between 1990 and 2008) appear to show no statistically significant variation (at the 5 % level) due to landfall location, which allows us to pool characteristics for the entire Bay of Bengal. We find that the natural variability of cyclone parameters translates into large uncertainty both for storm surge height (of the order of metres) and for coastal inundation (hundreds of km2). Using the variability estimates for a 1-in-50-year cyclone event making landfall at the 2007 Sidr location, cyclone central pressure drop uncertainty had the greatest effect upon simulated storm surge magnitude. However, uncertainty within cyclone track characteristics (track speed, landfall and genesis location) has greater influence on subsequent inundation extent. Storm surge hazard uncertainty due to cyclone parameter variability was found to be comparable to the inundation difference simulated when the peak surge coincided with either a mean spring high or low water. Our research indicates the importance of improving extreme water level estimates along the Bay of Bengal coastline for robust flood hazard management decisions in the Bay of Bengal.