Study On The Risk Assessment Of Typhoon Strom Tide In China Coastal Area

In the context of global warming and sea level rise, typhoon storm tide disasters risk of coastal area have been the hotspots in international society as well as the frontiers of science in research field. On the basis of the achievements of previous development in disaster risk research, this research presents the definitions and relationship model of typhoon storm tide disaster and risk. Moreover, the theoretical model and method system of typhoon storm tide disaster risk assessment have been built up. Considering the multi-temporal-spatial scale and regional characteristic of typhoon storm tide disaster impacts, different suitable methods have been used for the risk assessments in China coastal zone, typical coastal city (Shanghai), and coastal tidal river (Huangpu river) respectively. The followings are main works and conclusions of this research:(1) This research explores the theoretical and method system of typhoon storm tide disaster risk assessment. The general and special definitions of typhoon storm tide disaster and the relationship between disaster and risk have been distinguished. There is big uncertainties in the change trend of future typhoon storm tide disaster risk. On this base, typhoon storm tide disaster risk assessment framework has been built up, mainly including risk identification, risk analysis, and risk evaluation. In addition, the research focuses on the analysis of the relationship of disaster system and the classification of disaster loss. At last, the relative and absolute risk assessment methods have been proposed with the detailed illustration of the advantages and disadvantages, applicable scope, and risk assessment flow of the both methods.(2) Based on the risk identification of typhoon storm tide disaster in China coastal zone, findings show that there are a complex disaster-prone environment, the severe historical disaster loss, and a variety of disaster-causing mechanisms. The relative risk assessment method was employed and a indicator system which included two aspects of hazard and vulnerability with 14 indicators was built up for the comparative risk assessment of China coastal zone (not including Taiwan and remote islands). The analytic hierarchy process (AHP) was used to calculate the weight of each indicator, and the comparative risk assessment model was built up then. The results indicated that there were not very high or very low risk area in China coastal zone. Out of the 18000-km-long China coast,30.99% was under low risk mostly along the coastal hill-mountain zone, Hainan and Guangxi coast; most (62.71%) part of coastal zone was classified as moderate risk. Although only 6.30% of the total was under the high risk, the affected area mainly distributed in Tianjin, Shanghai, and Guangzhou of the three main delta with low topography, highly developed economy and highly-dense population.(3) Shanghai was selected as study area for the demonstration of typhoon storm tide disaster risk assessment of coastal city. On the basis of risk identification, findings show that the risk mainly induced by inundation from levee breach or extreme tide. Therefore, two sites of levee breach were selected to set up 6 return period inundation scenarios. Additionally, a prediction of future extreme tide has been generated using an algebraic summation of the relative sea level rise, storm surge, and astronomical tide.2D hydrodynamic model of FloodMap and a GIS-based seed spread algorithm have been used to simulate the inundation scenarios of levee breach and extreme tide. Furthermore,7 direct loss functions for different land uses were fitted using field investigation data and summary of previous studies. The different land use values were identificated by some related standards.5 indirect loss rates were also determined on the basis of previous studies. The results showed that the inundation area and the loss were both small in levee breach scenarios, therefore the risk was low. However, at the future extreme tide, almost all land of Shanghai would be under direct risk of flooding with extremely inundation depth (most above 5 m). By then, the total loss would be more than 200 billion yuan, and Shanghai would be destructed. It would be a unacceptable risk for Shanghai.(4) Huangpu river was selected as study river for the demonstration of typhoon storm tide disaster risk assessment of coastal tidal river.9711 typhoon storm tide was simulated and calibrated using 1D and 2D hydrodynamic model of FloodMap. The simulation was coincide with the actual situation, and the parameter combination could be used for scenario analysis. Based on the tide records of past 61 years, the height of annual maximum tide level have been selected and measured that allow for the construction of frequency curves using P-â…¢distribution to determine the probability of flood occurrence. The result of frequency analysis was compared with previous researches, findings indicated that tide levels of different frequency have increased remarkably, the 1000 return period design tide level of floodwall along Shanghai Bund was only the same as the present 200 return period tide level. Scenarios with 5 return periods tides and extreme tide have been simulated by using FloodMap model. The population vulnerability has also been assessed on the basis of population statistics data of each town or district. The results showed that in 5 return period scenarios, typhoon storm tide would mainly serious impact the 1-2km buffer areas of Huangpu river. At the future extreme tide, the inundation radius, inundation area, maximum inundation depth, and total loss would be more than 4km,374.19km2,6.84m, and 89.4 billion yuan separately. In this case, Huangpu river basin would be destructive impacted. It would be a unacceptable risk for Huangpu river.As one of the most seriously affected areas in the world, China coastal area need to establish a scientific and practical typhoon storm tide disaster risk assessment paradigm. In spite of this research have systematic explored theory, method and case study for typhoon storm tide disaster risk assessment, there were some shortcomings due to the complexity of diverse factors in typhoon storm tide disaster system. The improvements could be made in multi-hazards scenarios and comparative risk assessment, catastrophe risk assessment and response, and multi-temporal-spatial scale risk assessment and scaling to support disaster risk reduction and risk management in coastal area.