Risk Assessment And Adaptive Strategy Of The Compound Scenarios Of Sea Level Rise And The Probable Maximum Storm Surge

Coastal areas are centers for intensive socio-economic activities.In the context of the global climate change and rapid urbanization,the coastal areas are extremely susceptible to sea level rise and storm surge,regarding the high exposure of both people and assets to the risk.Therefore,it has attracted growing concern and research interest to improve the ability of resisting extreme disasters,and establish a warning system to enhance the reginal security.Take the coastal megacity—Shanghai as the study area,this study assessed the integrated hazards of and socio-economic vulnerability to the sea level rise(SLR),the probable maximum storm surge(PMSS),and the compound scenarios of sea level rise and probable maximum storm surge(SLR-PMSS),through the method of numerical simulation and scenario analysis.To this end,a scenario matrix was constructed to incorporate the effect of SLR,PMSS and SLR-PMSS.Based on the evaluation results,we attempted to formulate a strategy framework as disaster response for the study area.Major contributions and findings of this study are as follows.(1)Generate the scenario matrix of sea level rise in the Yangtze Estuary.Based on the previous research on sea level rise in the study area,we put forwarded three schemes to generate the target SLR scenarios.First,in the light of the Fifth Assessment Report of IPCC,three Representation Concentration Pathways(RCPs)—RCP2.6,RCP4.5 and RCP8.5—were concerned,and the prediction values in the Lvsi gauge station were chosen as the reference.Second,according to the Sea Level Bulletin of the State Oceanic Administration(SOA),the average of the prediction values on SLR of East China Sea and the Yangtze Estuary were calculated.Third,based on the historical average annual tide level data in Wusong and Lvsi gauge stations,the auto-regressive moving average model and the sin curve fitting algorithm were used to estimate the prediction values of SLR in the study area.As for all of the 5 groups of prediction values(each group has the highest,the average,and the lowest prediction value),the year 2013 was set as baseline,and 2030,2050 and 2100 as the targets.Finally,a scenario matrix comprising 45 sea level rise scenarios were obtained.(2)Construct the scenario matrix of the probable maximum storm surge in Shanghai.First,using the best track data sets of northwest Pacific tropical cyclones from 1949 to 2016(obtained from the China Meteorological Administration),frequency analysis of the probability distribution of the lowest center pressure and landfall pressure was conducted.Second,the peripheral pressure was set based on the measured annual average sea level pressure in Baoshan and Xujiahui meteorological station from 1981 to 2010(data acquired from the Shanghai Meteorological Bureau).Third,according to the empirical wind pressure relationship and the data of historical typhoon which influenced Shanghai,the maximum wind speed and maximum wind radius were estimated.Next,two moving directions of typhoons were designed based on the landfall typhoons which influenced Shanghai from 1949 to 2016.Note that to seek the balance between simulation accuracy and efficiency,parameters including the start and end locations,the moving speed,and the duration of typhoons were set subjectively.Finally,a scenario matrix comprising 60 different scenarios of the probable maximum storm surge was constructed.(3)Assess the hazard of sea level rise,probable maximum storm surge,and the compound scenarios of sea level rise and the probable maximum storm surge(called as “storm flooding” for short).Based on the numerical simulation and scenario analysis results,the impact of sea level rise is relatively mild,but the impact of the probable maximum storm surge is quite severe on the study area.With SLR becoming increasingly remarkable,the coastal wetlands would shrink continuously.Besides,the ecotype in coastal wetland would be reversed,including the mudflat and vegetation regions.The existing mudflat will be submerged until it disappears,and the vegetation regions will continuously shrink or even degenerate into the mudflat.Under the PMSS scenarios,large land area would be inundated,especially in suburban islands and the northern urban area(including part areas in Puxi and Pudong New Area).The impact of storm flooding as well as the inundation area would further increase with the growing PMSS intensity.Differently,the SLR factor mainly affects the inundation depth,but the PMSS determines the inundation extents.(4)Assess the risk of the compound scenarios of sea level rise and the probable maximum storm surge.MIKE 21 was used to simulate the storm flooding under multiple scenarios to year 2030 and 2050.Additionally,inundation depth,inundation area,potential population losses and direct economic losses were selected as the key factors to assess the socio-economic losses caused by the storm flooding.Specifically,loss models are established between water depth and mortality,as well as the land use.Simulation results indicate that flood risk increases with the typhoon intensity.The impact of storm flooding triggered by the 75° moving direction typhoons is more serious than that caused by the 32° typhoons.Inundation areas are mainly located in the northern suburbs of Shanghai,including the three suburban islands(Chongming,Changxing and Hengsha)and several districts in the urban area(Jiading,Baoshan,Yangpu districts in Puxi and the northern and southeastern in the Pudong New area).The population density in these areas are similar,but the landuse are quite different.Chongming is mainly for agricultural,but Baoshan,Jiading and Pudong gathered a large number of factories.Therefore,the most serious inundation can result in large mortality in Chongming,but cause huge economic losses in the other districts.(5)Formulate a strategy framework for resisting the impactes of sea level rise and the probable maximum storm surge.In general,the framework contains both the engineering and the non-engineering strategies,and emphases the significance role of four aspectes — defend,discharge,accumulate and permeate — that are critical for dealing with flood disasters.The engineering strategies(e.g.,construction of seawalls and flood-walls,promotion of drainage,and waterlogging and conduct of reservoirs),which take the dominance,should be associated with non-engineering strategies(e.g.,building the ecocity,planning the emergency evacuation and improving the disaster awareness).