Study On Risk Assessment Theories, Methods And Applications Of Urban Water Security

With the rapid growth of population and development of social economy, water security has become a major problem on environment and resources and attracted wide attention worldwide, such as water shortages, water environment pollution, soil erosion, flood and drought disaster, etc. Study on urban water security is especially important since city is the most frequent and complicated area with human activity. State diagnosis and prediction provide the theoretical basis for designing the scientific plan and making rational decisions of urban water security. It refers to nature, social, economic, environment, and so on. Risk is universal and inevitable objectively because of many uncertain factors in urban water security. Guided by the complex system theory and risk analysis theory, enlightened by relevant previous research of the domestic and international research on risk assessment of urban water security, the theory and method of state diagnosis and prediction for urban water security, and risk on water supply and water resources allocation are studied in detail and deeply. The main contents of this paper include seven aspects:(1) The research background and significance are provided. Considering the domestic and international researches on risk assessment of urban water security, the main research contents and technical route are proposed.(2) Based on the basic concept of urban water security and the definition of risk, definition, connotations and diagnosis method of urban water security are analyzed. The domestic and international researches on evaluation criterion of urban water security are summarized. Uncertainty of urban water security is analyzed and potential risk sources of which are identified. The main content of risk assessment implementation is introduced systematically from four aspects, including risk characteristics, principle of risk assessment, the dynamic procedure of risk analysis and the main risk description methods.(3) Constructive principle of indicator system is analyzed. The comprehensive evaluation indicator system for urban water security is developed from four aspects, including urban size, flood control security, water supply security and water environment security. Combinational weight method, which makes full use of the methods to subjectively or objectively determine the weight and does the subject and object unite, is proposed. To overcome the defects of traditional catastrophe evaluation method, the method is improved form two aspects. And the improved method is applied in the diagnosis of urban water security. The model is applied to evaluate the water security of nine cities in Wuhan urban agglomeration. (4) Water Security Index Model (WSIM) is established from several aspects, including designing indicator system, normalization of indicators, determining evaluation criterion, computation of water security index and so on. The model evaluates water security through composite index. The Spearman coefficient of rank correlation is applied to comparing the results of the model with other methods, what's more, the efficiency and rationality of the model is verified. The grey prediction model of urban water security is established to predict the trend of water security. Assessment of water security in Wuhan urban agglomeration and Wuhan city verify the feasibility and effectiveness of these models and methods.(5) The definition of water supply risk is discussed and on this basis, risk factors in water supply system are identified. Stochastic simulation model of water supply based on Box-Cox data transform technique is established by Box-Cox data transferring and stochastic simulation methods based on objective and subjective probability. Stochastic simulation model of water demand based on Copula function is established by Copula function theory and stochastic simulation techniques. Then the risk assessment model of urban water supply is developed. Especially for the water-rich city, risk assessment model under drought conditions is proposed. Five indicators, including reliability, resilience, vulnerability, water shortage index and coordination index are selected to establish risk evaluation indicator system.(6) Based on the concept and role of water resources allocation, uncertainty in the process of allocation is analyzed. The definition of water resources allocation risk is provided, and main risk factors are identified. Then the uncertain characteristics of different risk factors are described in quantity with subjective or objective probability distribution. Considering the remarkable feature of cloud model that transforming a qualitative concept to a set of quantitative numerical values, cloud based multi-objective optimization algorithm (CBMOOA) is developed. Coupling allocation model, Monte Carlo stochastic simulation and CBMOOA, the risk model of water resources allocation is developed. Taking Nanchang city as a study area, water allocation risks under two different water supply conditions are calculated.(7) The main research contents and achievements of this paper are summarized, and the topics that need further investigation are outlined.