Water-carbon nexus of hydropower: The case of a large hydropower plant in Tibet, China

Under the increasing crisis of a worldwide watershed water shortage and the pressing carbon emission reduction requirement, making clear the water-carbon nexus of hydropower plants will help co-resolve the contradiction in a significant water-carbon related issue. Simulating the water-carbon nexus of a biomass energy plant, this study calculates the water-carbon nexus of a hydropower plant, which represents the water utilization amount per unit greenhouse gas (GHG) reduction. The water utilization of a hydropower plant is composed of absolute water evaporation loss and temporary water storage loss. For the Zhikong hydropower plant in Tibet, 0.704 m3 of water is utilized when achieves a unit kg GHG reduction, and 0.126 m3 of water is evaporated when keeps a cubic meter of water in reservoir storage. With regards to the accumulated water-carbon nexus, a biomass energy system is more efficient in achieving a GHG reduction than the Zhikong hydropower plant in the first three years of operation, but thereafter the Zhikong hydropower plant is more efficient. The water-carbon nexus has identified a new direction for allocating watershed water resources to maximize GHG reduction potential, and also can be an indicator against which to manage watershed water resources in an efficient and sustainable way.