Does the implementation sequence of adaptive management countermeasures affect the collaborative security of the water-energy-food nexus? A case study in the Yangtze River Economic Belt.

• Development trend of collaborative security in middle reaches is considerable. • Collaborative security levels of Sichuan, Hunan and Jiangxi are lowest in 2020. • Bellman optimal equation is used to calculate expected benefits of measures. • Quantitative assessment is conducive to the collaborative security of the nexus. • Optimal implementation sequences of indictors with poor performance are proposed. Water, energy, and food are essential for human survival, and the production and consumption of these three resources are closely related. In the backdrop of limited resources and constantly expanding demand, the collaborative security of the water-energy-food nexus (WEF-nexus) is under serious threat. It is of great practical significance to study the adaptive management countermeasures of the collaborative security of the WEF-nexus in the Yangtze River Economic Belt (YREB) and to quantitatively evaluate the implementation sequence of relevant management countermeasures to improve the collaborative security and promote the sustainable development of the WEF-nexus. This study first establishes an evaluation indicator system for the collaborative security of the WEF-nexus in the YREB by utilizing the pressure-state-response (PSR) model. Then, the CRITIC and TOPSIS methods are used to determine the weight of indicators and the collaborative security level of the WEF-nexus in each province and city. The state transition matrix is determined based on the transition at the collaborative security level. Finally, based on the barrel theory to make up for shortcomings, the adaptive management countermeasures of provinces and cities with low collaborative safety levels are studied by combining the Bellman optimal equation. By comparing the expected returns of the same countermeasure in different implementation sequences and conducting quantitative research on the implementation sequence of adaptive management countermeasures, targeted policy suggestions are proposed based on regional characteristics, providing a reference for strategic decision-making of relevant resources in the YREB and improving regional WEF-nexus collaborative security. The results show that: (1) For Jiangxi, improving the water conservancy engineering regulation and storage capacity and other ways in a particular order can effectively improve the collaborative security level of nexus. (2) For Hunan, increasing the investment proportion of agriculture, forestry and water conservancy and resource exploration intensity and other means in a particular order can effectively improve the collaborative security level of the nexus. (3)For Sichuan, increasing the water-saving irrigation rate according to a particular order and other ways can effectively improve the collaborative security level of nexus. [ABSTRACT FROM AUTHOR]