| Under the background of global climatic warming and rising sea level, urban population and wealth are accumulating, the urban infrastructure system is more complicated, and the urban system is becoming more exposure and vulnerable to natural hazards with the continuous promotion of urbanization. Due to the influence of global climate change and human activities, natural disaster in urban area is becoming more and more serious. Located in the Yangtze River Delta, Shanghai plays a leading and exemplary role in Chinese socio-economic development and construction. Like many other typical coastal cities in China, Shanghai has suffered the impacts of rainstorm waterlogging disasters in recent years. Supported by the National Natural Science Foundation of China "Scenario Analysis of Emergency Responses to Natural Disasters Risk in Coastal Cities" and East China Normal University Reward for Excellent Doctors in Academics, the framework and methodological procedure for rainstorm waterlogging risk assessment in the typical costal city was proposed with the consideration of hazard-affected bodies'characters in urban area. Then the present study takes Shanghai, which is deeply affected by rainstorm waterlogging disaster as research area to conduct the empirical study. The research results are as follows:(1)This paper analyzed the type, composition and characteristic of urban floods based on systematic analysis of the structure of urban system. Then, we discussed the composition and the characteristics of urban flood risk system based on the understanding of the concept of risk of urban flood disasters. Finally, this paper proposed the method and technological process of risk assessment of rainstorm waterlogging on the aboveground buildings and the underground facilities based on scenario analysis respectively, considering the characteristics of different hazard-bearing bodies in coastal city.(2)In macroscopic view, the occurring frequency of flood disasters in Shanghai was relatively high. Moreover, there was an imbalance in the time distribution of flood disasters occurrence. The number of flood disasters in Shanghai changes upward trend over time. The flood type within the range of Shanghai is dominated by waterlogging disaster, especially after the establishment of New China. There were increasing trends for both the number of waterlogging disaster and that of storm surge disaster. The shape of the frequency curve of waterlogging disaster was consistent with that of flood disaster.(3) From micro aspect, the flood disaster within each district and county of Shanghai is dominated by waterlogging disaster from251to2000except in Chongming County. In addition, the flood disaster within the range of Shanghai is dominated by waterlogging disaster from1949to2000. Although each district in Shanghai had its own characteristic of flood disaster in different times, there was an imbalance in the time distribution of flood disasters occurrence in each district and county in Shanghai. The frequency curve of flood disaster in Minhang District was inverted U curve. There was an increasing trend for the number of flood disaster in the rest of Shanghai.(4)The analysis results of flood disaster data in Shanghai from251to2000show that Qingpu, Pudong, Minhang, Jiading, Baoshan, Songjiang and Fengxian should pay more attention to the risk control of overflow-type flood, Jinshan has medium overflow-type flood risk, Shanghai central urban area and Chongmin County show low overflow-type flood risk. Pudong New Area belong to high waterlogging risk area, Minhang, Baoshan and Qingpu belong to medium waterlogging risk area, and Jiading, Shanghai central urban area, Songjiang, Fengxian, Jingshan and Chongming have low waterlogging risk rank. Pudong New Area has high-risk rank of storm surge; Baoshan, Minhang and Chongming belong to medium risk area of storm surge, and Jiading, Qingpu, Shanghai central urban area, Fengxian and Jinshan show low storm surge risk. Overall, Pudong and Minhang have high-integrated risk rank; Baoshan, Qingpu, Jiading and Songjiang belong to medium integrated risk area, and Fengxian, Jinshan, Shanghai central urban area and Chongming show low integrated risk.(5)The analysis results of flood disaster data in Shanghai from1949to2000show that Qingpu has high overflow-type flood risk rank, Songjiang, Jinshan, Jiading, Baoshan and Chongming belong to medium overflow-type flood risk area, and Fengxian, Pudong, Minhang and Shanghai central urban area show low overflow-type flood risk. Shanghai central urban area belongs to high waterlogging risk area, and the rest of Shanghai shows low waterlogging risk. Shanghai central urban area, Pudong and Baoshan have high storm surge risk rank, Songjiang, Jingshan, Fengxian, Minhang and Chongming belong to medium storm surge risk area, Qingpu and Jiading show low storm surge risk. Overall, Shanghai central urban area, Qingpu and Baoshan have high-integrated risk rank, Pudong, Songjiang and Jinshan belong to medium integrated risk area, and Chongming, Jiading, Fengxian and Minhang show low integrated risk. Flood risk control in Shanghai central urban area is indeed a priority item.(6)The impact of land use and land cover change, which is the typical dynamic change of urban waterlogging disaster formative environments in Shanghai Pudong New Area, was analyzed. The results show that the land use structure and pattern change increases surface runoff depth. Moreover, the changes of average depth of surface runoff induce by land use and land cover changes are different at various stages of rapid urbanization process. There was a significant increase of surface runoff depth from1994to2000. The surface runoff depth increased continuously from2000to2003, although not as high as it would has. The increase of surface runoff depth was apparent recovery from2003to2006. With the improvement of urbanization, the change of land use structure and pattern not only altered urban waterlogging disaster formative environments but also altered the structure and pattern of the hazard-bearing bodies of urban waterlogging disaster. The afore-mentioned effects brought by land use and land cover change increases the probability of urban waterlogging disasters take place.(7) The paper established the simplified urban waterlogging model for the inundated water depth simulation through the combination of SCS model and GIS spatial analysis with the consideration of underlying surface characters in urban area. The model is effective and simple for calculation with less simulation time and less workload. (8)The analysis results of rainstorm waterlogging risk of subway in Shanghai central urban area show that the waterlogging risk of subway lines was not very high. The total number of subway station exit which affected by waterlogging disaster was only40, occupying11.6%of the total number. Shanghai West Railway Station exit1and Loushanguan Road Station exit3have high waterlogging risk rank. The number of subway station exits with medium waterlogging risk was18. There were20subway station exits, which have low waterlogging risk rank. Overall, Subway line2and line11belong to high waterlogging risk subway line, line4, line8and line10have medium waterlogging risk rank, and line1, line7and line9show low waterlogging risk.(9)The analysis results of rainstorm waterlogging in Shanghai central urban area show that the hazard caused by precipitation with different intensities presents spatial disparities evidently. The hazard of waterlogging caused by different precipitation is different. The hazard of waterlogging increased as the precipitation intensity increases. The hazard of waterlogging in different area in Shanghai central urban area caused by the same precipitation is different. Overall, Yangpu, Changning and Hongkou have high hazard rank; Xuhui, Putuo and Zhabei belong to medium hazard area, and Jing'an, Huangpu and Luwan show low hazard.(10)The analysis results of the exposure of residences to rainstorm waterlogging in central urban area of Shanghai based on scenario simulation show that the exposure of residences in different area presents spatial disparities evidently. The exposure of residences to waterlogging disaster increases as the rainstorm intensity increases. Overall, Yangpu, Putuo and Xuhui are the important regions for the government to carry out safety defense, Changning, Zhabei and Hongkou have medium exposure rank, and the waterlogging brings little effects in Huangpu, Jing'an and Luwan. The results indicate that the old-style residences and the warehousing are the most vulnerable building types when exposure to waterlogging disasters.(11)The vulnerability analysis results of residences to waterlogging in Shanghai central urban area show that the descending order of the vulnerability of residences' structure to waterlogging disasters is the old-style residence>the new-style residence>the villas-style residence. The disaster loss rate of residences'structure and content loss rate of residences increases as the rainstorm intensity increases. In addition, the type of damaged residence increases as the precipitation intensity increases. The rainstorm waterlogging disaster has serious effects on the residential structure in Yangpu, Putuo and Xuhui. The impact of waterlogging disaster on the residential structure in Changning, Zhabei and Hongkou stays on a middle level. The waterlogging brings little effects on the structure of residences in Huangpu, Jing'an and Luwan. The rainstorm waterlogging disaster has serious effects on the residential indoor property in Yangpu and Changning. The impact of waterlogging disaster on the residential indoor property in Putuo, Xuhui, Hongkou and Zhabei stays on a middle level. The waterlogging brings little effects on the indoor property of residences in Huangpu, Jing'an and Luwan. The results indicate that the residential indoor floor and the residential walls are the most vulnerable type of property when exposure to waterlogging disasters.(12)The analysis results of rainstorm waterlogging risk of residences in Shanghai central urban area show that the spatial difference of waterlogging risk of residences is very evident. The loss of residences increases as the rainstorm intensity increases. The average annual damage of residences in central urban area of Shanghai is22254166RMB. Moreover, the residence waterlogging risk in central urban area of Shanghai can be ranked as Yangpu>Putuo>Changning>Hongkou>Xuhui>Zhabei> Jing'an>Luwan>Huangpu. The frequency and intensity may change in the coming decades, which result in the waterlogging risk of residences in Shanghai central urban area always change due to global climate change and human activity.(13)The stage-damage curve and the functional relationship between the overall potential damages and the annual exceedance probability of rainstorm for the residences in central urban area of Shanghai were set up in the present research. In addition, we established the stage-damage curve and the functional relationship between the potential damages and the annual exceedance probability of rainstorm for the old-style residence, the new-style residence and the villas-style residence in central urban area of Shanghai respectively. This paper established the stage-damage curve and the functional relationship between the potential damages and the annual exceedance probability of rainstorm for the residence in each region of Shanghai central urban area based on the disaster situation in different scenarios.
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