It is essentially important to protect water resources and water eco-environment in the Qinghai-Tibet Plateau, the Asian water tower. Understanding water transfers through the trade of different products and services (i.e. virtual water transfers) and their influencing factors between Qinghai-Tibet Plateau and external regions can aid in analyzing local water resources problems and making virtual water strategies. Based on the China multi-region input-output table in 2012, this study calculated the virtual water transferred between Qinghai-Tibet Plateau and other regions in China. The virtual water transfer network comprising urban and rural nodes was constructed. Influencing factors that determine net virtual water trade of Qinghai-Tibet Plateau with other regions were analyzed using the Logarithmic mean Divisia index method. The results indicated that Qinghai-Tibet Plateau delivered a total of 0.23 billion m³ net virtual water to other regions in China. It delivered net virtual water to Southwest, North, Central, East and South China, and received net virtual water from Northwest and Northeast China. Intensive virtual water transfers between urban and rural regions were found. In the Qinghai-Tibet Plateau, production-based water footprint was higher in rural areas, whereas consumption-based water footprint was higher in urban areas due to high population density and consumption level. The node strength in rural areas of Qinghai-Tibet Plateau was higher than that in urban areas. In the plateau, the products transferred to other regions were dominated by agricultural products, which led to 1.27 billion m³ of virtual water export. The Qinghai-Tibet Plateau had a trade deficit with other regions, which resulted in 0.86 billion m³ of net virtual water export. Water use efficiency led to 0.18 billion m³ of virtual water export from the plateau. Water management policies were formulated towards sustainable water resources use. Irrigation water conservation needs to be implemented to reduce production-based agricultural water footprint, and urban inhabitants' consumption corresponding to a lower water footprint should be encouraged. In addition, net import of various products and water resources ecological compensation will be beneficial to water resources protection in the Qinghai-Tibet Plateau.

The continuous and intense human activities have greatly changed the structure, path and driving force of the natural water cycle evolution, which conversely influences the water security of human being. With the process of globalization and market economy, human activities not only affect the artificial development of water and soil resources, but also extend to the economic field. The "flow" of water trade contained in product has become an important internal factor that drives the evolution of the regional water cycle and affects regional water security. Traditional water cycle research, which focused on the watershed scale, is difficult to reveal the linkage, two-way feedback mechanism and co-evolution dynamic mechanism in water cycle among different regions. Starting from the phenomenon of continuous and water-intensive agricultural products export in Northwest China, this research elaborates the phenomenon, the process, the structure and their driving forces of the unitary natural water circular, nature-human society binary circular, and trading water circular within multi-regional social economic complex systems by theoretical analysis. We explicated the theoretical framework for constructing the "natural-social-trading" ternary water cycle in the inland river basin, including mode of process, driving force of water cycle, conceptual model, influencing factors and ecological environment effects. Furthermore, we discussed the frontier of water cycle research in inland river basin based on ternary water cycle model-social hydrology. We advocated that the future study on water cycle and water resources should focus more on the external forces driving the water cycle of the inland river basin and its two-way mutual feedback and co-evolution, providing theoretical references for the decision-making of water security, ecological environment security and ecological civilization construction in inland river basins.