| Disastrous wave,storm surge and coastal inundation induced by typhoons pose a serious threat to people’s life and property security in the coastal areas,and Shandong coastal area includes the Yellow Sea and Bohai Sea,which is one of the sea areas that are attacked by typhoons.Therefore,it is necessary to systematically study the distribution characteristics,propagation processes and formation mechanisms of wave,storm surge and coastal inundation induced by typhoons in Shandong coastal area,which will help us better understand the process of marine disasters caused by typhoons and make a good job in disaster prevention and disaster mitigation.This paper mainly focuses on Shandong coastal area and the corresponding unstructured computing grid with a high resolution is constructed.Based on the SWAN+ADCIRC coupling model,relying on ERA5 and CFS wind fields,the numerical simulations of several typical typhoons(including No.1909 Typhoon Lekima,No.1109 Typhoon Muifa and No.9216 Typhoon Polly)occurred in Shandong coastal area have been carried out;the distribution characteristics and disaster-causing mechanism of wave,storm surge and coastal inundation induced by typhoons are explored,and the evolution trend of typhoon storm surge-induced inundation risk in Shandong coastal area under global warming is analyzed.The main results of this paper are as follows:To begin with,using the measured data from buoys and tide gauge stations,the reliability of wind fields and coupling model was verified.The results showed that both ERA5 and CFS wind fields could well reproduce the typhoon wind field,ERA5wind field was better slightly than CFS wind field in terms of wind speed and typhoon moving path simulation.And the coupling model reproduced well the dynamic variation processes of astronomical tide,storm surge and significant wave height during typhoons.Based on the numerical simulation results of typhoon-induced wave in Shandong coastal area,the spatio-temporal distribution characteristics and influential mechanisms of typhoon-induced wave were investigated.The results showed that,the distribution characteristics between wave height and wind speed during typhoons are basically consistent,but the relationship on distribution characteristics between wave period and wave height(or wind speed)during typhoons are not obvious.The distribution of typhoon-induced wave during Typhoon Lekima in the Yellow Sea and Bohai Sea was mainly wind waves;during Typhoon Muifa,the distribution of typhoon-induced wave on the right side of the typhoon moving path was mainly wind waves,while the swell characteristic on the left side of the typhoon moving path was relatively obvious.Notably,a swell tongue was existed before the two typhoon centers went into the Yellow Sea.By using the dimensionless power-law wind-wave growth relationship(dimensionless wave height and dimensionless wave period)model and the quadratic polynomial wind-wave growth relationship(significant wave height and wind speed)model,the growth characteristics of typhoon-induced wave were analyzed,and the results showed that,the growth characteristics of typhoon-induced wave under different typhoon processes were consistent,and it was mainly related to the region where typhoons were located.The effect of wave-current interaction on growth and evolution of typhoon-induced wave was investigated,and the results showed that,the wave-current interaction could change the wave height from-1.22 m to 1.62 m;the current moving in the opposite direction(or in the same direction)of the wave would cause the increase(or decrease)of the wave spectrum energy or the decrease(or increase)of the wavelength;the simulation results of wave-current interaction obtained by different wind fields were basically consistent.The water depth(topographic effect)played a major role in modulating the wave height in the nearshore shallow region,and the wave height would increase as the water level enhanced,while the wind played a secondary role.Based on the numerical simulation results of typhoon-induced storm surge in Shandong coastal area,the spatio-temporal distribution characteristics and formation mechanisms of typhoon-induced storm surge were analyzed,and the results showed that,the strong wind blowing continuously toward the coast during the passage of typhoons and the shoreline restrictions caused the water level to accumulate towards the shoreline,and accompanied by the modulation of varying water depth and tide in the nearshore shallow water,which induced serious storm surge in the coastal regions of the Yellow Sea and Bohai Sea.The influence of wave effect on storm surge was investigated,and it was found that,the enhancement effect of wave setup(wave radiation stress)was mainly limited in the nearshore shallow water,but the enhancement effect of wave-induced wind stress was the cumulative effect of shoreline accumulation;wave setup(wave radiation stress)and wave-induced wind stress could contribute about 10%and 22%to the peak storm surge,respectively.The enhancement mechanism of wave-induced wind stress was analyzed,and the results showed that the significant enhancement effect of wave-induced wind stress on storm surge was mainly caused by young and fetch-limited waves with shoaling effect.The stronger increase in water level was not formed locally,which was mainly due to the cumulative effect of enhanced wind stress caused by wave in far sea.The wave-induced wind stress effect caused by wave strongly affected by water depth and topography was stronger in the Bohai Sea.Different parameterization schemes on wind drag coefficient were further discussed,and it was found that,the wave-steepness-dependent drag coefficient could significantly improve the simulation of storm surge,while the enhancement effect of wave-age-dependent drag coefficient was weaker.The inundation distribution along the Laizhou Bay was studied,and it was found that during 1981～2021,except for Typhoon Lekima and Typhoon Polly that induced an inundation area of more than 1200 km~2and an average inundation depth of more than 220 cm,the trend of coastal inundation was gentle in the other period,with a perennial inundation area of 300～650 km~2and an average inundation depth of 80～140 cm.The effects of wind fields and wave effects on coastal inundation were analyzed,and the results showed that,the coastal inundation caused by CFS wind field was 14.31%～23.05%larger than that caused by ERA5 wind field;the wave-induced wind stress could increase the coastal inundation area and average inundation depth by 11.42%～18.50%and 5.82%～8.75%,respectively,while the wave radiation stress could increase the coastal inundation area and average inundation depth by 3.80%～6.60%and 3.70%～4.57%,respectively.In the end,based on the simulated results on storm surge of 58 typhoons from1979 to 2017 and the mean sea level data from the official website of PSMSL,the variation trend of extreme storm surge induced by typhoons and the trend of sea level height change in Shandong coastal area were analyzed.The research results showed that the stronger extreme storm surge was mainly distributed in the Bohai Bay,Laizhou Bay,West Korean Bay,Gyeonggi Bay and southwest coastal region of the South Yellow Sea.The spatial variation trend of extreme storm surge induced by typhoons was about-10～10 mm/a.The results of tidal gauge stations indicated that,the mean sea level showed a significant rise trend,and its variation trend in height was 1.49～10.16 mm/a;compared to the mean sea level,the long-term variation trend of typhoon-induced extreme storm surge was not obvious.At the same time,the effect of sea level rise on coastal inundation was studied,and it was found that,the enhancement effect of sea level rise on storm surge-induced inundation mainly showed a duplicate effect,and it had not obvious nonlinear effect on storm surge;sea level rise could significantly increase the coastal inundation area but had little impact on the inundation depth;the variation of coastal inundation caused by sea level rise was related to the typhoon process.In addition,the return period of coastal inundation in the Laizhou Bay was calculated,and the results showed that the total average inundation depth along the Laizhou Bay was 225.84 cm,240.90 cm,252.19 cm and263.43 cm under the conditions of 20-year,50-year,100-year and 200-year return periods,respectively.The hazard level distribution of coastal inundation in the Laizhou Bay was illustrated,and it was found that,the inundation hazard in the coastal areas of the southwest bottom of Laizhou Bay was mainly Class I,which showed that its inundation risk was higher,and it was necessary to strengthen the disaster prevention and early warning work in the relevant regions.In conclusion,through a series of numerical experiments on marine dynamic processes,this paper discusses the coupling mechanism of storm surge and wave induced by typhoons and the evolution trend of typhoon storm surge-induced inundation risk in Shandong coastal area.The research results better reveal the process of dynamic marine disasters during typhoons in Shandong coastal area,which is conducive to the development of marine disaster warning and defense in the coastal areas,and it can provide some guidance to marine operational forecasting. |
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