Research On Rainstorm Waterlogging Risk Assessment Of Urban Communities

With global warming and the acceleration of urbanization, urban storm waterlogging has aroused great concerns of governments and experts. As the basic unit tomake up the modern city, the communities play an important role to reduce urbandisaster risk. Therefore, community-based disaster risk management has beenrecognized generally and is proven to be effective disaster management conceptsand means in recent years. Meanwhile, as the basis and premise ofcommunity-based disaster risk management, risk assessment has been one of thehotspots by scholars from various countries. In this paper, based on National NaturalScience Foundation of China “scenario analysis of natural disaster risk contingencyplans in coastal cities (40730526)” and Humanities and Social Sciences Youth FundProject of the Ministry of Education “PGIS-based community disaster riskmanagement model research (11YJCZH241)”, with the case of field study andresearch on typical urban communities (Jinsha Community Putuo District in Shanghai)and access to a large number of documents and first-hand data, an Empirical Study ofthe disaster risk assessment on typical urban community water logging are carriedout with use of PGIS methods, scenario analysis and probabilistic method. The mainresearch work and conclusions are as follows:1. Disaster risk assessment theory and methodology of urban communities’water logging are presented. Based on the analysis and definition of fundamentalconcepts of urban communities, water logging and disaster risk, and relative theoriesof disaster risk assessment, the framework of urban Community storm water loggingdisaster risk assessment is constructed which is the whole process of simulation,analysis, evaluation and expression of water logging disaster risk under differentscenarios in the study area with the participation of risk assessment experts and localstakeholders and integrated use of PGIS (participatory GIS), scenario analysis andprobability statistics. It mainly includes three major content points of riskidentification, risk modeling and analysis, and risk assessment and the expression,and is fulfilled by eight steps. 2. Urban communities’ water logging disaster risk assessment model isconstructed. Based on comprehensive analysis of the causes of urban water loggingand reference of existing water logging model, urban communities water loggingdisaster risk assessment model is built. It mainly includes three modules of waterlogging disaster database, urban communities’ water logging model and the urbancommunity risk models. Meanwhile, model parameters is verified and correctedthrough reconstruction of typhoon "anemone" water logging disaster in the studyarea in August2012which make the simulation results more consistent with theactual situation.3. Historical waterlogging disasters were analyzed in Shanghai. Based onhistorical data, historical waterlogging disasters were analyzed in Shanghai for nearly60years (1951-2010), which showed that:(1) urban natural environment was greatlyinfluenced by human activities, mainly representing as the impervious surfaceincreasing, ground subsidence and water area reduction. Meanwhile economicdevelopment, big population and densely urban infrastructure greatly increase therisk of floods;(2) from the perspective of time, the overall number of waterloggingdisasters was a growing trend and concentrated in June to August. From the spatialpoint of view, waterlogging disasters were the most at the central city, followed bythe coast, and inland counties were relatively the fewer;(3) Waterlogging disasterhas a strong diffusion effect. The diffusion channels are mainly composed of urbanlifeline systems, industrial chain and the ecological environment system, and etc. Andthe diffusion has influence on a variety of urban hazard-bearing body throughstraight diffusion, linear divergent diffusion, circulation diffusion and divergentdiffusion and so on.4. A comprehensive analysis of the residents’ perception on water loggingdisaster risk of the study area of Jinsha Community Putuo District in Shanghai withthe use of PGIS is conducted. In the detail, based on semi-structured questionnaires,interviews and field measurement methods of PGIS, community residents’ awarenessto water logging disaster risk is analyzed. It mainly includes three aspects of riskknowledge, risk attitudes and risk behavior. The results show that:(1) community residents believe that rainstorm water logging disasters each year occur3-4times onthe average, more concentrate in July to September and the main impact is in thecentral region of the study area;(2) community residents believe that there is someinfluence on families when the water depth is in the ankle and below (0-15cm), thereis greater influence on families when the water depth is in the calf and below(15-30cm) and there is the greatest influence on families when the water depth isover the calf (>30cm);(3) more than half of residents believe that water loggingdisasters is caused by nature. All residents take different measures in thepre-disaster, disaster and post-disaster, but don’t recognize or don’t attachimportance to the drains cleaning and clearing.5. Rainstorm water logging disaster risk in the study area is analyzed by use ofscenario analysis method. In the detail, rainstorm water logging risk in the study areain8return periods (5a,10a,30a,50a,100a,200a,500a and1000a) under4drainagescenarios (0mm/h,18mm/h,36mm/H and50mm/h) is simulated and analyzedbased on ArcGIS software and with the use of scenario analysis method. It mainlyincludes three sections of risk analysis, exposure analysis and vulnerability analysis.Risk analysis shows that:(1) under all scenarios, water logging risks are allconcentrated in Jinsha New Village and Jiefang Village which are in the central studyarea. The water area account for0%-47.8%of the total study area. The maximumaccumulation of water depth is between0and0.52meters which increases alongwith rainstorm growth in the return period and decreases along with the increase ofdisplacement.(2) Among32water logging disaster scenarios,21ones are high risk,9are middle risk and only2are low risk.(3) Among4drainage conditions, waterlogging risks at the return periods with200a and over are all high.(4) As thedisplacement increases, annual probability of exceedance of middle risk of waterlogging is reduced from100%to6.8%, annual probability of exceedance of high riskis reduced by26%to0.8%. Exposure analysis shows that:(1)Among a variety ofwaterlogging scenarios, the most households which is exposed to the risk are791and the least are0which are all located in the central study area with brick andwood houses.(2) The number of exposure households increases as the return periods of rainstorm increase and decreases as the displacement increases. But thedegree of reduction is inversely proportional to the size of the return periods.(3) atthe4kinds of drainage conditions,30,137, and216families in200a,500a and1000aare exposed to high-risk areas when there were rainstorms which we should focus onin water logging prevention and mitigation. Vulnerability analysis shows that:(1)waterlogging vulnerability is mainly reflected in three aspects of the households ofwalls, floors and indoor property;(2)under a variety of waterlogging scenarios, wallsurface loss rate of the majority of exposed families is between0-0.06, floor loss rateis1;(3) only under high risk water logging scenarios, indoor property of a fewexposed families would suffer a loss and the loss rate distribution is between0-0.12.6. Waterlogging disaster risk under a variety of scenarios in the study area isexpressed and evaluated. In the detail, based on risk analysis, Waterlogging disasterrisk under a variety of scenarios is expressed and evaluated from the perspectives oftime and space. research results show that:(1) waterlogging loss of the vast majorityof families is between$0-1000and these families are mainly located in Jinsha NewVillage in the central study area;(2) All types of loss increase with the increase of thereturn period rainstorm and decrease with increasing displacement, of which indoorproperty loss grows and reduces the fastest, followed by the loss of floor and wallloss grows and reduces the slowest;(3)According to the probability of exceedance-loss curve established on8return periods under4drainage scenarios, it is concludedthat average annual loss of waterlogging:25,895yuan under0mm/h drainagescenarios,10,672yuan under18mm/h drainage scenarios,6781yuan under36mm/h drainage scenarios and1937yuan under50mm/h drainage scenarios.Urban water logging disaster risk assessment is a complex systematic projectinvolving theories and methods of disasters, risk, geography, environmental studies,sociology and other disciplines. In this article, urban storm water logging disaster riskassessment is did some useful exploration from the perspective of community whichis only the beginning with respect to the expansion of scientific theory and realisticsolution to the problem. In the future, some works need to be studied and discussedin-depth in these aspects such as residents participation and local risk knowledge acquisition and application, risk assessment methods and paradigms at the citydifferent scale and dynamic risk assessment and empirical research.