Assessing the impacts of inter-basin water transfer projects on ecosystem services in water source areas: Evidence from the Hanjiang River Basin

Inter-basin water transfer projects (IBWT) are a key strategy for alleviating regional water shortages. However, studies on the long-term effects of such projects on ecosystem services (ESs) in water source areas, as well as their spatiotemporal evolution, remain insufficient. In particular, the specific impacts of the entire project lifecycle (project initiation, dam heightening, project operation, and ecological restoration) on ESs need further exploration. This study focuses on the Middle Route of the South-to-North Water Diversion Project in China, utilizing multi-source datasets (land use and land cover, meteorological data, soil texture, digital elevation models, normalized difference vegetation index, and net primary productivity), applying the biophysical model method to examine the spatiotemporal variations in ESs across the Hanjiang River Basin over the past three decades, and investigates the impact of IBWT on the ESs of water source areas. The findings reveal: (1) During the project initiation phase (2000-2010), vegetation restoration strategies enhanced soil retention by over 60%, demonstrating that simultaneous project-ecological implementation can mitigate habitat degradation risks. (2) The dam heightening phase (2005-2010) drove spatial reconfiguration of water-energy fluxes, leading to declines in water conservation and carbon sequestration in the midstream region, while enhancing flood mitigation and climate regulation in the reservoir area, unveiling the reshaping mechanisms of dam heightening on ESs supply patterns. (3) The operation phase exhibited significant temporal heterogeneity: initial operation (2010-2015) saw a sharp decline in water conservation (>40%) and soil retention (>60%) due to hydrological disturbances, whereas sustained operation (2015-2020) restored water conservation by nearly 70% and soil retention by over 40% through ecological restoration, alongside a net increase of 14.14% in carbon sequestration, confirming the time-lag compensation effects of restoration measures and the dynamic interplay between ecological restoration and project interventions. This research presents empirical evidence supporting the sustainable management and ecological restoration of IBWT, emphasizing the need to balance spatial water allocation with ecological conservation.