From the perspective of risk transmission process of basin water resources security, this paper systematically analyzes fundamental concepts, including the water resources security system, water resources security risk system, and water resources security risk assessment. The conceptual framework for water resources security risk assessment is proposed, which is characterized by an Aristotelian syllogistic relational structure and encompasses five elements: the hazard of risk-inducing factors, the vulnerability of risk-bearing bodies, the risk-inducing potential of hazardous environment, the risk-resistance capacity of mitigation measures, and the water resources security loss risk. This paper reveals the transmission mechanism of water resources security risk elements, where under specific risk-incubating and risk-resisting conditions in a watershed, the hazard of risk-inducing factors serves as the system input, the vulnerability of risk-bearing bodies as the system transition, and the water resources security loss risk as the system output. This paper elaborates on methodology for water resources security risk assessment, consisting of water resources security risk assessment objects, evaluation indicators, evaluation indicator measurement methods, methods for quantifying qualitative indicators, single-indicator evaluation methods, methods for determining indicator weights, and methods for determining comprehensive evaluation indicators. The theoretical framework composed of the conceptual system, risk transmission mechanism, and risk assessment methodology forms a preliminary theoretical foundation for water resources security risk assessment. This theoretical framework also holds significant application value for risk assessment in other resources and environmental systems.

In order to deeply reveal the application characteristics of set pair analysis in structural water resources methodology and look forward to its main development trends, combined with existing research results, based on the methodological perspective of relational structure, a three-element structural principle of structural water resources methodology system consisting of research object, research variable, and research objective (abbreviated as the Ternary Structure Principle) was summarized and proposed. Based on the principle, the application progress of ensemble analysis in modeling, optimization, identification, simulation, prediction, evaluation, decision-making, reasoning and other methods of structural water resources methodology was systematically expounded. It is pointed out that set pair analysis had obvious advantages in describing and handling the uncertain argumentation relationship between research variables and research objectives. The implementation process of the first seven methods reflects the information transmission between the research object, research variables, and research objectives, while the implementation process of the inference method reflects the information transmission between the evidence, argumentation, and conclusion relationship. Compared with the first seven methods, the abstraction and complexity level of the water resources system inference method are higher. The research approach of combining physical cause analysis of uncertainty formation process with quantitative calculation is an important development trend in the future to explore more systematic and pioneering water resource set pair analysis methods.

In order to quantitatively identify regional water resources carrying status and its obstacle factors, and to fully mine the micro-uncertainty between evaluation sample and grade criteria, this study proposed a calculation method of dynamic difference degree coefficient that continuously varied with the actual sample value. Then an evaluation and diagnosis model of regional water resources carrying capacity (WRCC) using connection number value was established, and an empirical study was carried out in Anhui Province. The results showed that the connection number value of WRCC in Anhui Province gradually increased from -0.171 in 2011 to 0.067 in 2018, indicating that although the water resources carrying situation in Anhui Province was still quite severe in recent years, the status of each city had been all improved, and the trend after 2013 was more significant. In addition, the average connection number values from 2011 to 2018 in Northern Anhui, Central Anhui, and Southern Anhui were -0.235, 0.071, and 0.114, respectively. It reflected that the water resources carrying situations in different regions of Anhui Province were markedly different, presenting a spatial distribution that the carrying situation of Southern Anhui was superior to that of Central Anhui, while the carrying situation of Northern Anhui was weak. Supplementing water resources amount, improving vegetation coverage, controlling water resources exploitation, increasing ecological water supply, and developing water-saving irrigation were effective means to improve the water resources carrying situation in Anhui Province. The application results of regional WRCC evaluation and diagnosis model based on dynamic difference degree coefficient are reasonable, which provides decision support for guaranteeing regional water security.