Transboundary water resources cooperation is of great significance to the sustainable development of human society and the protection of national water rights and interests. Based on historical transboundary water cooperation data from 1948-2008, this paper extracted and analyzed the cooperation relationships between 166 countries. By using social network analysis and level of analysis methods, the paper discussed the spatio-temporal evolution of transboundary water resources cooperation events and networks, as well as the generative mechanism and type of cooperation. We found that: Firstly, the number of events and the frequency of cooperation increased in fluctuation, and there were obvious phase changes. Secondly, the structure of the water cooperation network is characterized by multi-centrality, with a trend of decentralization, multi-polarization, and regionalization. The Eastern Bloc and the Western Bloc dominated global water cooperation in the Cold War era. Africa, Eastern Europe, and the surrounding areas of the Asian Water Tower have shown a high demand for water cooperation in the Post-Cold War Era. Thirdly, water cooperation is sensitive to geographical distances, and countries within the same basin interact frequently. Extraterritorial powers are involved in hotspot water cooperation affairs at different phases. Fourthly, state actors, regional cooperation relationships, and international cooperation system, represent three levels that comprehensively affect the generation of water cooperation relationships. And there are complex multi-factor interactions at each level. Coercive, utilitarian, normative, and ideological water cooperations are the four main types of transboundary water cooperation.

Since the international water crisis intensified, transboundary water cooperation has become the key to resolving the water crisis and achieving peaceful and sustainable development among countries. This study built international transboundary water cooperation networks based on transboundary water agreements, and used social network analysis and other methods to examine the spatial and temporal structure of transboundary water cooperation from the global, intercontinental and national scales. The conclusions are as follows: (1) The number of international transboundary water cooperation projects increased from 1820 to 2017, and the scope of cooperation expanded significantly. The cooperation issue area changed from border issues and water quantity to joint management and water quality. The purpose of the agreements changed from regulatory to generative, procedural and regulatory. Multilateral cooperation and transboundary groundwater cooperation are the current development trends in international transboundary water cooperation. (2) During the same period, there were differences in the development process and focus areas of transboundary water cooperation among the five continents. Europe and North America were dominated by water quality, Africa and South America were dominated by joint management, and Asia had similar cooperation proportions in three areas: water quality, water quantity and joint management. Although the global transboundary water cooperation network covers more and more basins and countries, its coverage rate is still low. (3) The international transboundary water cooperation networks from 1820 to 2017 experienced three stages, namely, network formation, network expansion, and network differentiation. North American countries have a high degree of transboundary water cooperation, but due to geographical constraints, their cooperation targets are relatively single. After World War II, African countries have gradually dominated in the network. Since 1992, Asian countries have been increasingly active in the transboundary water cooperation network. The demand for transboundary water cooperation in Asian countries is growing. China, as a large responsible developing country, should strengthen transboundary water cooperation with neighboring countries, and actively promote transboundary water cooperation in Asia.

The core of transboundary river governance is the allocation of transboundary water resources. Based on the case study, four typical transboundary water resources allocation modes are summarized from the perspective of the interests relation among the riparian countries, including power mode, inheritance mode, gentleman mode and sharing mode. Then, the characteristics of the above modes are reviewed from the aspects of applicable conditions, negotiation and performance, operational efficiency and potential problems. The following suggestions are proposed for the allocation of water resources in transboundary rivers in China. First, we should reject the power mode and rely on the Belt and Road Initiative to get out of the hydro-hegemony discourse dilemma. Second, we should advocate the sharing mode and build the community of common destiny for transboundary water resources. Third, for transboundary river basins with relatively abundant water resources, it is advocated to innovate the regulation mechanism of transboundary water resources under special water conditions. Fourthly, it is of great significance to promote sharing by implementing virtual water trade strategy for transboundary river basins where water resources are relatively scarce. Finally, it is proposed to establish an independent and authoritative transboundary water resources coordination organization by eliminating external interference.