Ecological health assessment of the middle route of the South-to-North Water Diversion Project using an enhanced VORS model

The Middle Route of China’s South-to-North Water Diversion Project (MR-SNWDP) has substantially alleviated water scarcity in northern China and the water-receiving regions along its route. However, its impact on ecosystem health (EH) is also profound. This study focuses on the 27 urban regions along the middle route of the MR-SNWDP. Using land use data from 2000 to 2022 and Landsat imagery as a foundation, it constructs a research baseline based on remote sensing ecological indices (RSEI) for “vigor-organization-resilience-service (VORS)”. The study employs the Invest model to quantitatively assess ecosystem service provision from 2000 to 2022, revealing changes in EH before and after the water transfer. The research findings indicate that, between 2000 and 2022, land use was predominantly composed of cropland, forest land, and grassland, with frequent conversions between land types. The net loss of cropland reached 1,140,052 hm², primarily due to conversion into built-up land. Overall, the EH has improved, with a spatial distribution pattern showing that the southwest region exhibits better conditions compared to the northeast. Due to land use changes, the EH in the Beijing-Tianjin-Hebei (BTH) region has remained suboptimal. In terms of periods, prior to the water transfer (2000–2015), EH slightly declined, with reductions in ecosystem organization (EO), ecosystem resilience (ER), and ecosystem service (ES) values. Conversely, the ecosystem vigor (EV) value showed a notable increase. After the water transfer (2015–2022), EH showed a marked increase. Except for a slight decrease in ES values, all other indicator values exhibited varying degrees of improvement.