Numerical Simulation And Risk Evaluation Of Storm Surge And Coastal Inundation Induced By Typhoon In China Coastal Area

Every summer in the northern hemisphere,China's eastern and southern coastal areas are frequently suffering from tropical cyclones in the Northwest Pacific Ocean.In particular,tropical cyclones with the scale of typhoon induce destructive storm surge disaster and coastal inundation in the southeast coast of China,resulting in great economic losses and serious casualties.In addition,the ever expanding reclamation projects change the distribution of land and sea,thus affecting the hydrodynamic process in the coastal areas.Once the marine dynamic disasters occur,the consequences will be very serious.Therefore,it is necessary to do scientifically study on the risk of typhoon storm surge and coastal inundation.These can not only provide accurate forecast technology for storm surge,but also provide effective evaluation methods for coastal inundation risk in coastal areas of China.This study focus on the coastal of Zhejiang Province and the Pearl River Estuary(PRE)which are located in the southeast coast of China.The typhoon storm surge and coastal inundation are serious in these areas.In view of these two key areas,the main research contents and conclusions of this paper are as follows.A typhoon storm surge simulation system is established for Zhejiang coastal areas.This system is composed of an assimilation typhoon model and the ADCIRC + SWAN(Advanced Circulation Model + Simulating Waves Nearshore)coupled model.The assimilation typhoon model is obtained by effectively superimposing the wind speed and pressure of typhoons from the Holland typhoon model and the analysis data CFSR(Climate Forecast System Reanalysis)or the CFSV2(Climate Forecast System Version2).The system with high resolution can cover the complex and changeable bathymetry and topography of the coastal area.The reliability and the accuracy of the system are verified by simulating historical storm surges of the Zhejiang coastal areas induced by Typhoon Trami(2013)and Typhoon Fitow(2013).On this basis,this paper discusses how the scale of computational domain effect on the simulation results of typhoon storm surge.Upon the premise of high grid resolution in the offshore area,the size of the computational domain has no significant effect on the simulations of typhoon storm surge in Zhejiang coastal area.In order to improve the computational efficiency of the model,this study selects the computational mesh structure only including the East China Sea to complete the simulation experiments of typhoon storm surge in Zhejiang Province.Moreover,it is found that the assimilation typhoon model is more accurate for the Zhejiang's storm surge by comparing the simulated typhoon storm surge of the assimilation typhoon model and the asymmetric Holland typhoon model.In this paper,23 new typhoon tracks are designed basing on the historical Typhoon Sinlaku(2002),Typhoon Morakot(2009)and Typhoon Haikui(2012).Then of these typhoon tracks are analyzed to the risk of Wenzhou's storm surge.The influence of 55 historical typhoon tracks is classified and discussed on the storm surge in Zhejiang Province.A coastal inundation simulation system based on ADCIRC + SWAN coupled model is developed for the PRE,China.The unstructured triangular grid used in the system can not only cover the land and sea of coastal areas at the same time,but also automatically identify the dry grid and wet grid during numerical computing.The system is verified by simulating the historical typhoon storm surges and coastal inundations which are induced by Typhoon Hope(1979),Typhoon Nida(2016)and Typhoon Hato(2017)in the PRE.Some sensitivity experiments are used to analyze the influence of meteorological forcing fields,typhoon tracks,moving speeds of typhoon center and typhoon intensity on storm surge and coastal inundation.The results indicate that the contribution of wind forcing to storm surge and coastal inundation is greater than that of pressure forcing,and their nonlinear interaction tends to weaken the disaster intensity.The relative position between typhoon tracks and the coast of the PRE significantly affects the intensity of the storm surge and coastal inundation.In this study,the track of Typhoon Hato(2017)is the easiest to cause storm surge and coastal inundation in the PRE.Coastal inundation behaves more sensitively to the moving speed of typhoon centre than storm surge.The effect of typhoon intensity on storm surge and coastal inundation is similar.In recent years,the reclamation projects obviously affect the shape of coastline,land topography and nearshore bathymetry in the PRE,China.Three sets of computational meshes are constructed based on the coastlines of 1973,1990 and 2018,which are used to simulate the wave height,storm surge and coastal inundation in the PRE during the Typhoon Nida(2016).The results of simulation indicate that the reclamation project reduces the significant wave height of the PRE,but it is not obviously.Thus,the reduction of the significant wave height has little effect on weakening storm surge and coastal inundation in the PRE.In the area with high rate of reclamation in the PRE,the nearshore flow velocity is accelerated,and storm surge and coastal inundation are enhanced.43 coastal inundation events from 1998 to 2018 are simulated for the PRE basing on the coastal inundation system.Then the 20 years' extreme coastal inundation is obtained.The Gumbel method and Weibull-III method are used to fit the extreme value of coastal inundation in the whole computation domain.Then the 10-year,50-year,100-year,and 200-year return coastal inundations are obtained.The results indicate that the coastal inundation with deeper depth and larger area will occur in or nearby the area with higher rate of reclamation.On this basis,1 m is set as the threshold of inundation depth,and the risk level of coastal inundation is analyzed for the PRE.According to the probability that the inundation depth is more than 1 m,the risk of coastal inundation is defined as five grades.The coastal inundation risk zoning map is drawn and shows that the risk of coastal inundation in Nansha District of Guangzhou,Jinwan District of Zhuhai and the Inner Lingding Bay are generally high.In conclusion,this study analyzes the risk of typhoon storm surge for Zhejiang Province,discusses the influence of typhoon characteristics and coastline changes on typhoon storm surge and coastal inundation for the PRE.All of these provide theoretical basis and technical guidance for the disaster prevention and mitigation of marine dynamic disasters in the southeast of China.In addition,it is also of great significance to the development of operational forecasting technology and risk evaluation methods of typhoon storm surge and coastal inundation.