Major Natural Disaster Risk Assessment Of Tianjin Binhai New Area

Natural disaster is the hotspot question in international society and academe. Coastal cities are important areas and strategic focus of people convergency,national economy and society development.However,natural disasters happen easily and frequently in these areas.Tianjin Binhai New Area(TBNA) lies in the center of the Bohai Rim Region.Following the Shenzhen Special Economic Zone and Pudong New Area,TBNA becomes a new polarization of economic development which drives regional growth.Affected by physical-geographical conditions and human activities, TBNA is one of the areas where the loss from natural disasters is very fierce and fatal in the coastal areas in China.This dissertation will provide bases of theory and scientific tools for natural disaster risk management model,emergency plan and sustainable development model. This dissertation was financially supported by the National Natural Science Foundation of China(No.40730526,No.40571006 and No.70703010).Based on the analysis of change characteristics of major natural disaster by Empirical Mode Decomposition(EMD) and Mann-Kendall test and its formation mechanism,this dissertation assessed the risk of land subsidence,torrential rain and storm surges in TBNA respectively by probability analysis,scenarios simulation,GIS and hydrological mathematical model.Based on the assessment result,specific strategies were put forward for natural disaster risk management.Several main conclusions are shown as follows:(1)The main characteristics of major natural disaster in TBNA are as follows:the accumulative subsidence is large but the trend of land subsidence is slow;sea level rises persistently,and is higher in flood season;the precipitation tends to decrease in general,annual distribution of precipitation is uneven,and frequency and intensity of the torrential rain have an obvious increasing tendency;the annual high tidal level continues high,the monthly distribution of the annual high tidal level is uneven,the frequency of storm surge increases continually,and the disaster is very fierce.(2)Based on the system approach and the natural disaster risk index theory,an indicator framework for assessing the land subsidence risk was designed,in which there were 3 first level indicators(the hazard,the vulnerability,and the capability of disaster prevention and reduction) and 9 second level indicators.The very high risk and high risk areas were mainly in the part of the Hangu downtown,Hu Jiayuan Sub-district,Hang Zhoudao Sub-district,Xiangyang Sub-district,Xingang Sub-district,Gegu Town,Zhongtang Town,and Xiao Wangzhuang Town.(3)Different from sudden disasters,land subsidence is a slow-onset geohazard and accumulated over years.In terms of the main causing factor,the numerical model of land subsidence was established.With three groundwater extraction scenarios,the computer program was compiled to predict the land subsidence in the process of dynamic changes of groundwater level.Maintaining the same condition of groundwater exploitation in 2007(Scenario 1),from 2007 to 2020,the maximum accumulative subsidence in TBNA will be 650ram and the average accumulative subsidence will be 268mm.With 2%decreases in groundwater exploitation year by year(Scenario 2),the maximum accumulative subsidence will be 520mm and the average accumulative subsidence will be 177mm.With the water from South-to-North Water Transfer Project replacing groundwater exploitation completely (Scenario 3),the maximum accumulative subsidence will be 150mm and the average accumulative subsidence will be 95mm.To 2020,the loss induced by land subsidence under Scenario 1,Scenario 2 and Scenario 3 will be 122.21×10~8yuan,80.71×10~8yuan, and 43.32×10~8yuan respectively.(4)Based on GIS,the calculation model of flood submerged area was established. The submerged area and depth were calculated by the module of"non-source flood". On the basis of the loss rate of different submerged depth,the submerged loss was gained.In accordance with the GDP of Tianjin Binhai area in 2007 and present situation for land use,the submerged area is 22.85%,20.06%and 16.42%;and the loss of submerged is 28.16×10~8yuan,23.89×10~8yuan and 18.46×10~8yuan respectively induced by torrential rain with return period of 1000,200,and 50 years.(5)To 2020,three scenarios were design.Scenario 1:268mm average subsidence and 55mm sea-level rise;Scenario 2:177mm average subsidence and 40mm sea-level rise;Scenario 3:95mm average subsidence and 24mm sea-level rise.In accordance with population scale,GDP,and land allocation in 2020 by master plan,under Scenario 1,the submerged area is 32.73%,29.34%and 26.01%;inundated population accounts for 225～338×10~4,203～305×10~4 and 176～264×10~4;and the loss of submerged is 220.89×10~8yuan,181.39×10~8yuan and 139.12×10~8yuan respectively induced by torrential rain with return period of 1000,200,and 50 years.Under Scenario 2,the submerged area is 30.70%,27.47%and 24.23%;inundated population accounts for 212～318×10~4,193～289×10~4 and 165～248×10~4;and the loss of submerged is 199.68×10~8yuan,150.31×10~8yuan and 126.03×10~8yuan respectively induced by torrential rain with return period of 1000,200,and 50 years.Under Scenario 3,the submerged area is 29.06%,25.83%and 22.58%;inundated population accounts for 200～300×10~4,179～268×10~4 and 150～224×10~4;and the loss of submerged is 174.48×10~8yuan,135.29×10~8yuan and 111.53×10~8yuan respectively induced by torrential rain with return period of 1000,200,and 50 years.(6)According to representative storm surge in history and the existing tidal barrier, tidal influx volume of storm surge in different frequency was calculated by hydrological mathematical model,and the submerged area of storm surge in different frequency was calculated by the module of"source flood".The Gumbel method was used to calculate the annual high tidal level in different frequency.The annual high tidal level is 4.54m,4.92m and 5.08m in the frequency of 5%,1%and 0.5%.The submerged area account for 5.25km~2,58.38km~2 and 118.50km~2;and the loss of the submerged is 1.79×10~8yuan,3.93×10~8yuan and 5.06×10~8yuan respectively induced by storm surge in the frequency of 5%,1%and 0.5%.(7)In accordance with result in risk assessment of major natural disaster,this dissertation proposed the implementation strategies for the natural disaster risk management and suggestions on implementation of the natural disaster risk management in TBNA.