| Urban natural disaster risk is the spotlight in international disaster and abroad researchfield. Because both the frequency and the intensity of global natural disasteroccurrences are increasing, the research on urban natural disaster risk is drawing moreattention in international professional field as well as in domestic related field. In2005, the researcher of this paper take part in two National Science Fund Committeeprogrammes, which are Comprehensive Risk Assessment and Management ModeResearch on Natural Disaster in Coastal Cities, and key programme ScenarioAnalysis on Natural Disaster Emergencies in Coastal Cities. During the researchperiod, the researcher collects a great number of literatures and research data. On theadvanced bases, the paper summary the achievement of previous development innatural disaster risk research both in domestic and abroad for references. Starting fromearth systemic and scientific thought, the paper makes analysis on the maincharacteristics of natural disaster risk system and probes into the theories and methodsof natural disaster risk assessment. The paper apply Remote Sensing and GIStechniques to take apart the dynamic assessment ways and modes of natural disasterrisk in diverse scales cities, in order to provide scientific basis for urban disaster riskdecreasing and risk decision-making management. The followings are mainconclusions of the research:1.Research analysis and practices indicate that it is unrealistic to make exactforecasting and preventing natural disaster, but adopting the results of scientificnatural disaster risk assessment and strategic management can avoid or alleviate thegreat losses; Urban natural disaster risk may focus on the degree of human societyexposure to surroundings, the vulnerability of disaster acceptor; and risk express.Urban natural disaster risk system is provided with characteristics of chain dominoeffect, magnify domino effect and man-made effect, etc. Getting help frommulti-datum gaining methods and complicate system imitated to model, whichsimulates the evolvement process of disaster happening under the disturbing situation of human behavior, to make a dynamic assessment on disaster risk.2. Starting from earth systemic and scientific thoughts, the paper set up urban disasterclassification system according to cause of formation and grade sequence principle.Corresponding earth surface layer and human activity system, the natural disaster andman-made disaster belong to the first grade, which is the environmental system totrigger disasters. The second grade includes weather disaster, hydrological disaster,geological disaster, biological disaster, which are formed in atmosphere, hydrosphere,lithosphere and biosphere in the earth surface layer. And technological disaster andman-made disaster attribute to humankind and technique, and so on. Environmentaldisaster attribute to both humankind and nature, which is operated by humankindsystem and nature system altogether. The third grade is the further classificationaccording to the cause of formation of diverse disaster types, just as the weatherdisaster which has typhoon, ice and snow, storm tide, etc. Such kind of urban disasterclassification system based on cause of formation of disaster and environment system,it is propitious to recognize and analysis the surrounding which trigger to disaster, andin view of different surroundings, it can help to make analysis on risk andvulnerability, and put forward corresponding decision making and managementcountermeasures on disaster reducing and risk debasing.3. The paper built up a relation mode which connect urban natural disaster system,disaster risk system and disaster risk assessment. Urban natural disaster risk systemand disaster system has a lose relationship. Risk system is a subsystem of disastersystem. Urban disaster system contains pregnant disaster environment, hazards anddisaster acceptor. And urban natural disaster risk system based on the analysis on boththe danger of hazards and vulnerability of disaster acceptor, and further analysis onthe exposing elements processed by the hazards and vulnerability of disaster acceptor.Urban natural disaster risk may due to three points: hazards, the degree of humansociety exposure to surroundings, and the vulnerability of disaster acceptor; The papermakes an expression of disaster risk via disaster loss assessment and disastercost-benefit analysis. 4. The paper makes a probe into multi-scale system on urban natural disaster riskassessment. The urban natural disaster risk assessment is related to the scale ofresearch field, spatial resolution, administrative unit and the precision of data.According to both from top to bottom and from bottom to top two scales researchmethods, the paper formed city,district and community three scales to develop thedisaster risk assessment. City scale, research map scale 1:500000～1:100000, relatedunit spatial resolution 250m～30m, district scale, research map scale 1:100000～1:10000, related unit spatial resolution 30m～5m, community scale, research map scale1:10000～1:1000, related unit spatial resolution is below 5m. So different researchscale refer to different assessment methods, the big scale research generally use indexsystem assessment way, and middle and small scale research use scenario simulationand disaster investigation on scenario spot. And in order to meet the need of differentassessment precision, the same scale research can make use of different riskassessment methods, and the same risk assessment method can apply to different scaleresearches.5. Selecting index system risk modeling mode and method, based on hazards, disasterhistories, exposure and vulnerability, and resilience of disaster resisting, choosing 19risk assessment indexes, the paper set up Shanghai natural disaster integrated riskassessment index system. Taking all Shanghai municipal districts as assessing primaryunits, the paper makes use of Delphi method and AHP to certain each index value.The paper makes a processing of standardization to get each index factor andintegrated risk value, which has 10 grades from bottom to top, and make use of GIS tomap Shanghai integrated risk. It indicates:①There are great differences aboutexposure-vulnerability index in each districts, the greatest are Huangpu district andJing'an district.②2 The risk value of each district is in middle grade of risk grades, thegreatest is 0.75 in Huangpu district, the lowest is 0.38 in Jinshan district.③Theintegrated risk grades present radiate descending from Shanghai downtown to suburb.④The risk value of coastal districts is above 0.5, which is higher than the 0.4 in westdistricts. This index system method can be used for reference to assessing urban riskin a quick step. 6. Making use of dynamic risk assessment method based on scenario analysis, thepaper makes flood disaster risk assessment on Jing'an district. Starting from hazards,vulnerability and exposure analysis, and applying remote sensing and GIS to simulatedifferent scenarios of 8 return periods within one-hour-rain inundation area andinundation depth, and display the simulating result by three-dimensional visualizationway. And thorough field survey and data selecting, the paper makes a relation curvechart between the loss of citizen housing and treasure and the inundation degree. Thepaper makes assessment on population suffering from disaster and loss, according tothe exposing analysis on people and houses inundation situation, and makes use ofexceedance probability-loss curve to form risk sequence and count the AverageAnnual Flood Loss, which can help make cost-benefit analysis on disaster decreasing.The analysis indicates:①According to the exceedance probability-loss curve basedon 8 return periods situations in Jing'an district, the Average Annual Flood Loss is3.42 million.②2 According to 8 return periods scenario simulation on flood, thedeepest is 50cm.③The risk assessment method can advance urban DEM, andpromote the spatial analysis precision of scenario simulation, and it makes a moreexact assessment result, which can help flood risk management.7. Taking Linyuan community's flood, Pudong district, Shanghai Sep. 20th, in 2008 asexample, the paper makes several multi-scenario simulations with remote sensing andGIS, through the field survey. And it measures the different submerging spots andinterpolating base on the spots; simulate the flood scenario with the analysis ofhazards, vulnerability and exposure. According to citizen houses and contentsexposing and losing rate, it gets the total loss is 608732 Yuan, the return period is 150years, exceedance probability is 0.0067, the Average Annual Flood Loss(Risk value)is about 4079 Yuan, which is in line with the actual. This provides a new probe forflood disaster data collecting and risk assessment method in urban community scale.Urban natural disaster risk system is a complex system, and it is restricted by a lot ofdiverse factors, which leads to the complexity and difficulty of the whole disaster riskassessment system. The paper makes a research and discussion on urban naturaldisaster risk system, but it needs more hard work and study to make further developments in this field in future, which, for example, includes to pay moreattention to urban disaster data-base construction to provide the standard mode andsharing materials for disaster data management, to strengthen case study on urbannatural disaster risk, and to form the vulnerability curves of different type disasteracceptors, to study on natural disaster risk assessment mode in urban multi-scale torealize the dynamic assessment of integrated disaster risk, to provide foundation andcountermeasures on disaster decreasing and risk reducing for every level ofgovernment.
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