Contribution of water use to water vapor recirculation rate in the water-receiving area of the Haihe River Basin in the Middle Route of the South-to-North Water Diversion Project
The implementation of the Middle Route of the South-to-North Water Diversion Project has a great impact on the water vapor recirculation process and water cycle mechanisms in the water-receiving areas. To investigate the impact, the ERA5 reanalysis data from 2000 to 2022 and water resources bulletin data of four provinces and municipalities in the water-receiving areas were used for the analysis. We calculated the water vapor recirculation rate, analyzed its spatiotemporal trends and the influencing factors using Brubaker binary model, and further examined the contributions of different sectors to water vapor recirculation rates from the water use perspective. The results indicate that precipitation and actual evapotranspiration in the study area decreased during 2000-2022, while water vapor input increased. The water vapor recirculation rate showed an overall downward trend, with a reduction rate of 0.54‰/a, which accelerated after the water diversion. After the implementation of the Middle Route of the South-to-North Water Diversion Project, the water vapor generated by water diversion primarily entered from the western, northern, and southern boundaries, and exited from the eastern boundary. The enhanced external water vapor input caused the water vapor recirculation rates in all cities to decrease to varying degrees, with a greater impact on water vapor input regions. The water vapor recirculation rates of the agricultural and industrial sectors in the study area showed a decreasing trend from 2000 to 2022 and prior to water diversion, while those of the residential and ecological sectors showed an increasing trend. After water diversion, the water vapor recirculation rate in the ecological sector increased significantly at 1.37‰ per year, representing an increase of 0.84% compared with pre-diversion levels. Meanwhile, the water vapor recirculation rate in the agricultural sector decreased by 1.39%, which is greater than the overall level (0.57%) and that in the industrial sector (0.17%).