Assessment of typhoon storm surge disaster scale based on expansion model

The South China Sea suffers strongly from the typhoon storm surge disasters in China,and its northern coastal areas are facing severe risks.Therefore,it is necessary and urgent to establish an assessment system for rating typhoon storm surge disaster.We constructed an effective and reliable rating assessment system for typhoon storm surge disaster based on the theories of over-threshold,distribution function family,and composite extreme value.The over-threshold sample was used as the basis of data analysis,the composite extreme value expansion model was used to derive the design water increment,and then the disaster level was delineated based on the return period level.The results of the extreme value model comparison show that the Weibull-Pareto distribution is more suitable than the classical extreme value distribution for fitting the over-threshold samples.The results of the return period projection are relatively stable based on different analysis samples.Taking the 10 typhoon storm surges as examples,they caused landfall in the Guangdong area in the past 10 years.The results of the assessment ranking indicate that the risk levels based on the return period levels obtained from different distributions are generally consistent.When classifying low-risk areas,the classification criteria of the State Oceanic Administration,China(SOA,2012)are more conservative.In the high-risk areas,the results of the assessment ranking based on return period are more consistent with those of the SOA.

Numerical simulation of typhoon- induced storm surge on the coast of Jiangsu Province,China,based on coupled hydrodynamic and wave models

In order to facilitate engineering design and coastal flooding protection, the potential storm surge induced by a typhoon is studied.Using an unstructured mesh, a coupled model which combines the advanced circulation （ ADCIRC ） hydrodynamic model and simulating waves nearshore （ SWAN ） model is applied to analyze the storm surge and waves on the coast of Jiangsu Province.The verifications of wind velocity, tidal levels and wave height show that this coupling model performs well to reflect the characteristics of the water levels and waves in the studied region.Results show that the effect of radiation stress on storm surge is significant, especially in shallow areas such as the coast of Jiangsu Province and the Yangtze estuary.By running the coupled model, the simulated potential flooding results can be employed in coastal engineering applications in the Jiangsu coastal area, such as storm surge warnings and extreme water level predictions.

Simulation of Storm Surge and Wave Due to Typhoon Isewan(5915)

An integrally coupled wave-tide-surge model was developed and then applied to the simulation of the wave-typhoon surge for the typhoon Isewan （typhoon Vera （5915））, which is the strongest typhoon that has struck Japan and caused incalculable damage. An integrally coupled tide-surge-wave model using identical and homogeneous meshes in an unstructured grid system was used to correctly resolve the physics of wave-circulation interaction in both models. All model components were validated independently. The storm surge and wave properties such as the surge height, the significant wave height, wave period and direction were reproduced reasonably under the meteorological forcing, which was reprocessed to be close to the observations. The resulting modeling system can be used extensively for the prediction of the storm surge and waves and the usual barotropic forecast.

Numerical simulation of typhoon-induced storm surge along Jiangsu coast,PartⅡ:Calculation of storm surge

The Jiangsu coastal area is located in central-eastern China and is well known for complicated dynamics with large-scale radial sand ridge systems. It is therefore a challenge to simulate typhoon-induced storm surges in this area. In this study, a two-dimensional astronomical tide and storm surge coupling model was established to simulate three typical types of typhoons in the area. The Holland parameter model was used to simulate the wind field and wind pressure of the typhoon and the Japanese 55-year reanalysis data were added as the background wind field. The offshore boundary information was provided by an improved Northwest Pacific Ocean Tide Model. Typhoon-induced storm surges along the Jiangsu coast were calculated based on analysis of wind data from 1949 to 2013 and the spatial distribution of the maximum storm surge levels with different types of typhoons, providing references for the design of sea dikes and planning for control of coastal disasters.

Numerical Study of Storm Surge Inundation in the Southwestern Hangzhou Bay Region During Typhoon Chan-Hom in 2015

Storm surge inundation is a major concern in marine hazard risk assessment during extreme weather conditions.In this study,a high-resolution coupled model(the ADVanced CIRCulation model+the Simulating WAves Nearshore model)was used to investigate the storm surge inundation in the southwestern Hangzhou Bay region during Typhoon Chan-hom in 2015.The simulated hydrodynamic processes(sea surface wave and storm tide)were validated with measured data from wave buoys and tide gauges,indicating that the overall performance of the model was satisfactory.The storm surge inundation in the coastal area was simulated for several idealized control experiments,including different wave effects(wave-enhanced wind stress,wave-enhanced bottom stress,and wave radiation stress).Dike overflowing cases with different dike heights and dike breaking cases with different dike breach lengths were considered in the simulation.The results highlight the necessity of incorporating wave effects in the accurate simulation of storm surge inundation.Dike height significantly influences the magnitude and phase of the maximum inundation area in the dike overflowing cases,and dike breach length is an important factor impacting the magnitude of the maximum inundation area in the dike breaking cases.This study may serve as a useful reference for accurate coastal inundation simulation and risk assessment.

The effect of wave-induced radiation stress on storm surge during Typhoon Saomai(2006)

The effects of wave-induced radiation stress on storm surge were simulated during Typhoon Saomai using a wave-current coupled model based on ROMS （Regional Ocean Modeling System） ocean model and SWAN （Simulating Waves Nearshore） wave model. The results show that radiation stress can cause both set-up and set-down in the storm surge. Wave-induced set-up near the coast can be explained by decreasing significant wave heights as the waves propagate shoreward in an approximately uniform direction; wave-induced set-down far from the coast can be explained by the waves propagating in an approximately uniform direction with increasing significant wave heights. The shoreward radiation stress is the essential reason for the wave-induced set-up along the coast. The occurrence of set-down can be also explained by the divergence of the radiation stress. The maximum wave-induced set-up occurs on the right side of the Typhoon path, whereas the maximum wave induced set-down occurs on the left side.

THE STUDY OF STORM RAINFALL CAUSED BY INTERACTION BETWEEN THE NON-ZONAL HIGH LEVEL JET STREAK AND TYPHOON IN THE DISTANCE

In this paper, statistics were analyzed concerning correlation between the storm rainfall far from typhoon and non-zonal upper-level jet stream. The results show that the jet stream at 200 hPa is constantly SW (90.2 %) during the period in which storm rainfall occurs. Rainfall area lies in the right rear regions of the jet axes. While the storm intensifies, the jet tends to be stronger and turn non-zonal. With the MM4 model, nu-merical simulation and diagnosis were carried out for Typhoon No.9711 (Winnie) on August 19 to 20, 1997. The distant storm rainfall is tightly correlative to the jet and low-level typhoon trough. The divergence field of jet is related to the v component. The upper level can cause the allobaric wind convergence at low level. This is the result of the form of low-level typhoon trough and the strength of the storm. By scale analysis, it is found that there is a branch of middle scale transverse inverse circulation in the right entrance regions behind the jet below the 300-hPa level, which is very important to the maintenance and strengthening of storm rainfall. This branch of inverse circulation is relative to the reinforcement of jet’s non-zonal characteristics. From the field of mesoscale divergence field and non-zonal wind field, we know that the stronger symmetry caused by transverse circulation in the two sides of the jet, rainfall抯 feedback and reinforcement of jet抯 non-zonal characteristics had lead to positive feedback mechanism that was favorable of storm rainfall抯 strengthening.

Parameterization and Application of Storm Surge/Tide Modeling Using a Genetic Algorithm for Typhoon Periods

A genetic algorithm was used to optimize the parameters of the two-dimensional Storm Surge/Tide Operational Model （STORM） to improve sea level predictions.The genetic algorithm was applied to nine typhoons that affected the Korean Peninsula during 2005-2007.The following model parameters were used：the bottom drag coefficient,the background horizontal diffusivity,Smagorinski＇s horizontal viscosity,and the sea level pressure scaling.Generally,the simulation results using the optimized,mean,and median parameter values improved sea level predictions.The four estimated parameters improved the sea level prediction by 76% and 54% in the bias and root mean square error for Typhoon Kalmaegi （0807） in 2008,respectively.One-month simulations of February and August 2008 were also improved using the estimated parameters.This study demonstrates that parameter optimization on STORM can improve sea level prediction.

ANALYSIS OF CAUSATION OF ASYMMETRIC PRECIPITATION ASSOCIATED WITH SEVERE TYPHOON DAMREY

Severe typhoon Damrey moved across Hainan Island from 00:00 UTC 25 September to 00:00 UTC 27 September in 2005 and gave rise to a significant rain process during its 48-h passage.The precipitation intensity on the southern part of the island is stronger than that on the northern,showing obvious asymmetric distribution.Using Tropical Rainfall Measuring Mission(TRMM) data,the associated mesoscale characteristics of the precipitation were analyzed and the formation of asymmetric rainfall distribution was investigated in the context of a subsynoptic scale disturbance,vertical wind shear and orographic factors.The results are shown as follows.(1) The subsynoptic scale system provided favorable dynamic conditions to the genesis of mesoscale rain clusters and rainbands.(2) The southern Hainan Island was located to the left of the leeward direction of downshear all the time,being favorable to the development of convection and leading to the asymmetric rainfall distribution.(3) Mountain terrain in the southern Hainan Island stimulated the genesis,combination and development of convective cells,promoting the formation of mesoscale precipitation systems and ultimately resulting in rainfall increase in the southern island.

Numerical simulations and comparative analysis for two types of storm surges in the Bohai Sea using a coupled atmosphere-ocean model

The Bohai Sea is extremely susceptible to storm surges induced by extratropical storms and tropical cyclones in nearly every season. In order to relieve the impacts of storm surge disasters on structures and human lives in coastal regions, it is very important to understand the occurring of the severe storm surges. The previous research is mostly restricted to a single type of storm surge caused by extratropical storm or tropical cyclone. In present paper, a coupled atmosphere-ocean model is developed to study the storm surges induced by two types of extreme weather conditions. Two special cases happened in the Bohai Sea are simulated successively. The wind intensity and minimum sea-level pressure derived from the Weather Research and Forecasting (WRF) model agree well with the observed data. The computed time series of water level obtained from the Regional Ocean Modeling System (ROMS) also are in good agreement with the tide gauge observations. The structures of the wind fields and average currents for two types of storm surges are analyzed and compared. The results of coupled model are compared with those from the uncoupled model. The case studies indicate that the wind field and structure of the ocean surface current have great differences between extratropical storm surge and typhoon storm surge. The magnitude of storm surge in the Bohai Sea is shown mainly determined by the ocean surface driving force, but greatly affected by the coastal geometry and bathymetry.

Numerical Investigation of High Tide Level Due to A Super Typhoon in A Coastal Region

A numerical model of the couphng between astronomical tide and storm surge based on Mike 21 is applied to the coastal regions of Zhejiang Province. The model is used to simulate high tide levels combined with storm surge during 5 typhoons, including two super typhoons, that landed in the Province. In the model, the atmospheric forcing fields are calculated with parametric wind and pressure models. The computational results, with average computed errors of 13 cm for the high astronomical tide levels and 20 cm for the high storm-tide levels, show that the model yields good simulations. Typhoon No. 5612, the most intense to land in China since 1949, is taken as the typical super typhoon for the de- sign of 5 typhoon routes, each landing at a different location along the coast. The possible extreme storm-tide levels along the coast are calculated by the model under the conditions of the 5 designed typhoon routes when they coincide with the spring tide. Results are compared with the high storm-tide levels due to the increase of the central atmospheric pressure at the base of a typical super typhoon, the change of tidal type, and the behavior of a Saomai-type typhoon. The results have practical significance for forecasting and minimization of damage during super typhoons.

A numerical study on the impact of tidal waves on the storm surge in the north of Liaodong Bay

A storm surge is an abnormal sharp rise or fall in the seawater level produced by the strong wind and low pressure field of an approaching storm system.A storm tide is a water level rise or fall caused by the combined effect of the storm surge and an astronomical tide.The storm surge depends on many factors,such as the tracks of typhoon movement,the intensity of typhoon,the topography of sea area,the amplitude of tidal wave,the period during which the storm surge couples with the tidal wave.When coupling with different parts of a tidal wave,the storm surges caused by a typhoon vary widely.The variation of the storm surges is studied.An once-in-a-century storm surge was caused by Typhoon 7203 at Huludao Port in the north of the Liaodong Bay from July 26th to 27th,1972.The maximum storm surge is about 1.90 m.The wind field and pressure field used in numerical simulations in the research were derived from the historical data of the Typhoon 7203 from July 23rd to 28th,1972.DHI Mike21 is used as the software tools.The whole Bohai Sea is defined as the computational domain.The numerical simulation models are forced with sea levels at water boundaries,that is the tide along the Bohai Straits from July 18th to 29th（2012）.The tide wave and the storm tides caused by the wind field and pressure field mentioned above are calculated in the numerical simulations.The coupling processes of storm surges and tidal waves are simulated in the following way.The first simulation start date and time are 00：00 July 18th,2012; the second simulation start date and time are 03：00 July 18th,2012.There is a three-hour lag between the start date and time of the simulation and that of the former one,the last simulation start date and time are 00：00 July 25th,2012.All the simulations have a same duration of 5 days,which is same as the time length of typhoon data.With the first day and the second day simulation output,which is affected by the initial field,being ignored,only the 3rd to 5th day simulation results are used to study the rules of the storm surges in the north of the Liaodong Bay.In total,57 cases are calculated and analyzed,including the coupling effects between the storm surge and a tidal wave during different tidal durations and on different tidal levels.Based on the results of the 57 numerical examples,the following conclusions are obtained：For the same location,the maximum storm surges are determined by the primary vibration（the storm tide keeps rising quickly） duration and tidal duration.If the primary vibration duration is a part of the flood tidal duration,the maximum storm surge is lower（1.01,1.05 and 1.37 m at the Huludao Port,the Daling Estuary and the Liaohe Estuary respectively）.If the primary vibration duration is a part of the ebb tidal duration,the maximum storm surge is higher（1.92,2.05 and 2.80 m at the Huludao Port,the Daling Estuary and the Liaohe Estuary respectively）.In the mean time,the sea level restrains the growth of storm surges.The hour of the highest storm tide has a margin of error of plus or minus 80 min,comparing the high water hour of the astronomical tide,in the north of the Liaodong Bay.

Effects of cluster land reclamation projects on storm surge inJiaojiang Estuary,China

Variations in coastline geometry caused by coastal engineering affect tides, storm surges, and storm tides. Three cluster land reclamation projects have been planned for construction in the Jiaojiang Estuary during the period from 2011 to 2023. They will cause significant changes in coastline geometry. In this study, a surge-tide coupled model was established based on a three-dimensional finite-volume coastal ocean model （FVCOM）. A series of numerical experiments were carried out to investigate the effects of variations in coastline geometry on tides, storm surges, and storm tides. This model was calibrated using data observed at the Haimen and Ruian gauge stations and then used to reproduce the tides, storm surges, and storm tides in the Jiaojiang Estuary caused by Typhoon Winnie in 1997. Results show that the high tide level, peak storm surge, and high storm tide level at the Haimen Gauge Station increased along with the completion of reclamation projects, and the maximum increments caused by the third project were 0.13 m, 0.50 m, and 0.43 m, respectively. The envelopes with maximum storm tide levels of 7.0 m and 8.0 m inside the river mouth appeared to move seaward, with the latter shifting 1.8 km, 3.3 km, and 4.4 km due to the first project, second project, and third project, respectively. The results achieved in this study contribute to reducing the effects of, and preventing storm disasters after the land reclamation in the Jiaojiang Estuary.

A SIMILARITY SCHEME FOR QUANTITATIVE FORECAST OF PRECIPITATION OF TYPHOONS

A quantitative scheme is put forward in our work of forecasting the storm rainfall of typhoons for specific sites.Using the initial parameters,weather situations and physical quantities as well as numerical weather prediction products,the scheme constructs multivariate,objective and similarity criteria for environmental factors for the time between the current and forthcoming moment within the domain of forecast.Through defining a non-linear similarity index,this work presents a comprehensive assessment of the similarity between historical samples of typhoons and those being forecast in terms of continuous dynamic states under the multivariate criteria in order to identify similar samples.The historical rainfall records of the similar samples are used to run weighted summarization of the similarity index to determine site-specific and quantitative forecasts of future typhoon rainfall.Samples resembling the typhoon being forecast are selected by defining a non-linear similarity index composed of multiple criteria.Trial tests have demonstrated that this scheme has positive prediction skill.

珠海市沿海风暴潮数值模拟试验研究

基于ELCIRC模型建立了适用于珠海市海域的风暴潮模型,以1713号台风“天鸽”路径为基础,通过改变台风入射角、台风登陆点、台风移速等方式构建登陆或者影响珠海市的台风路径,并进行风暴潮数值模拟计算,分析珠海市沿海风暴潮特征。结果表明:改变台风入射角时,珠海市沿海不同岸段的风暴潮将出现较大差异性;距离台风中心约15~100 km且位于台风右半圆的沿海地区将是风暴潮的重灾区;在珠海市的香洲区和斗门区沿岸,风暴增水总体随着台风移速变慢而呈现增大的趋势,但金湾区的情况则较为复杂,当台风移速为15~30 km/h时,在沿着台风“天鸽”的移动路径上会产生较强的风暴潮过程。

江苏沿海台风风暴潮特征分析

收集了1950—2022年影响江苏沿海的历史台风风暴潮过程资料,对引起江苏沿海台风风暴潮的台风路径进行了分类和分析,开展了江苏沿海台风风暴潮的月际分布和年际变化研究,提出了不同路径台风风暴潮的预报要点。结果表明:引起江苏沿海台风风暴潮次数最多的是外海转向型台风,占比高达44.3%,而正面登陆型台风最少,占比只有5.4%,但引起的增水量值最大;江苏沿海台风风暴潮在6—10月均有出现,8月出现次数最多;风暴潮强度等级为Ⅴ级(增水50~100 cm)的过程占比最多,为42.7%,而高潮位超警戒程度等级为Ⅳ级(超警戒30 cm之内或达到黄色警戒潮位值)的占比最多,为45.0%;风暴潮发生次数在近几年呈上升趋势,尤其是增水为50~100 cm的过程,高潮位超警戒或达到黄色警戒潮位值以上的过程在近20年只出现3次;在江苏沿海台风风暴潮的预报和应对中,需要重视可能正面登陆的和9—10月的外海转向型台风;8月和9月是江苏沿海出现风暴潮灾害可能性较高的月份,若这两个月的天文高潮与风暴增水叠加合适,极有可能出现达到黄色警戒潮位以上的高潮位。

长短期记忆神经网络(LSTM)对风暴潮数值模拟的优化应用

利用长短期记忆神经网络和数值模式相结合的方法,设计了两套针对粤东遮浪海洋站点台风风暴潮增水的预报优化方案。与实测资料对比结果显示,长短期记忆神经网络方法可以显著改善数值模式模拟结果的准确性,最大增水和主振过程中增水后报结果的平均绝对误差、平均相对误差和平均改善幅度分别为7.1 cm、8.2%、74%和16.1 cm、34.7%、33%。进一步分析表明,利用台风信息预测数值模拟结果的订正值可以有效改善神经网络方法的不稳定性,比直接预测风暴潮增水值更加准确、可靠。

考虑Copula-LM-HMS耦联的台风情境下大坝洪水漫顶风险率计算

气候变化下台风风暴潮出现频次增加,形成的暴雨洪水对水库大坝安全产生极大威胁。由于部分地区实测流量资料缺少,基于雨量资料的随机模型与水文模型耦合模拟洪水过程线的研究亟待发展。针对现有小流域流量资料缺少问题,研究了基于降雨随机模型与水文模型的Copula-LM-HMS耦联模型,来模拟入库洪水并计算水库大坝洪水漫顶风险率。该模型通过Copula函数与拉丁超立方-蒙特卡罗抽样(Latin Hypercube-Monte Carlo Simulation)生成流域多组7日降雨数据,并通过变倍比放大法缩放处理得到相应降雨序列,利用HEC-HMS水文模型模拟洪水过程线并结合调洪演算得到坝前最高水位,同时考虑风浪作用来模拟台风情景下的库水位变化情况,计算大坝洪水漫顶风险率,并分析不同组合条件对洪水漫顶风险率的影响。余姚市四明湖水库实例分析表明,构建的Copula-LM-HMS耦合模型计算得到的拦河坝在未来台风情境下无漫顶风险,自溃坝最小漫顶风险为0.22%,最大漫顶风险达到2.68%;洪水漫顶风险与降雨分布及起调水位有关,同时风浪作用对洪水漫顶风险影响较大。基于耦合模型进行中小流域洪水漫顶风险率计算,不仅能考虑降雨系列之间的相关性、流域地形特征与实际调洪规则,还可延长无流量资料地区水库大坝应对台风情境下洪水风险的预报期,为保证水库大坝应对未来气候变化影响下的运行安全提供参考。

极端天气下轨道交通水害致灾因子时空分布特征

近年来,在与气候变化相关的多种极端天气因素的相互作用下,洪涝事件对城市及轨道交通系统造成了严重影响。以粤港澳大湾区典型沿海城市洪涝事件为例,研究了轨道交通水害的主要致灾因子(极端降雨和台风风暴潮)及相关特征参数,揭示了其时空分布特征。研究表明:①近年来,广州市降雨量、降雨强度均明显增加,但降雨历时减少,降雨整体呈现增多且趋于集中的极端化趋势。广州市降雨时间分布在年内存在两个极值区间,第一极值区间与广州市“龙舟水”相关,第二极值区间主要受台风影响。广州市降雨空间分布不均,主要受季风及地理位置影响。②近10 a影响广东省的29场台风风暴潮灾害集中发生在7~10月,该时间与降雨第二极值区间重合。在对近年广东省典型轨道交通水害事件进行总结后发现,水害高发期与两个极值区间重合。虽然广东省台风强度存在缓慢降低趋势,但由于广东省沿海城市遭受台风风暴潮灾害的频次不断上升,且粤中地区密集分布有广东省全部的地下轨道交通系统,未来广东省轨道交通系统水害风险将随着极端天气时空分布特征的变化进一步加大。研究成果可为未来城市轨道交通水害致灾特征研究提供依据,为城市防灾减灾提供参考。

台风过境期间辽河口滨海湿地水动力特征的数值模拟研究

本研究基于FVCOM环流模型,耦合ECMWF背景风场和Jelesnianski台风经验模型形成合成风场,对9711台风“温妮”过境辽河口区域的水动力进行模拟研究。模型通过在动量方程、湍流方程中加入附加源项来表达盐沼植被对水动力的阻碍作用。使用研究区域实测的潮位、流速、流向等数据对水动力模型进行验证,模拟结果与实测数据吻合较好。结果表明:潮滩盐沼植被对台风过境期间的潮位变化无明显影响,但对流速具有显著的衰减作用,且芦苇对潮流的衰减作用大于盐地碱蓬植被,芦苇区的速度最大衰减率达81.43%。此外,台风路径变化对辽河口湿地海域的增减水及流速影响较大,台风强度越强,局部区域造成的风暴潮增水和流速也相应越大。