Optimal allocation of water resources in the middle route of south-to-north water diversion project based on multi-regional input-output model

Long-distance water diversion, as an essential degree to alleviate the imbalance of regional water resource distribution, has become a crucial part of the global efforts of water conservancy and water ecology. However, the way to ensure green use of water resources while adequately diverting water is an urgent hassle to be solved. Based on relevant data from 11 cities in the water receiving areas along the Middle Route of the South-to-North Water Diversion Project and Markowitz's portfolio model, this study selects nine independent and representative indicators from the economic, social, and ecological aspects. Using the benefits of these nine indicators in 2015–2021 as a basis, the water diversion allocation portfolio with the greatest comprehensive benefits under normal operation of the Middle Route of the South-to-North Water Diversion Project was calculated and evaluated, and the benefits were measured and verified using the input–output model. The results demonstrate that, taking Beijing as an example, the comprehensive benefits will reach the maximum when the water supplied for economic, social, and ecological aspects is 15.16%, 56.35%, and 28.49%, respectively. At this time, economic benefits scored 9.50, which provide the greatest impetus to promote ecological and social development in water-affected areas along the route. While ecological and social benefits, which aim to protect the ecosystem and improve livelihoods, have a lower ability to promote development in water-affected areas.