Satellite-based assessment reveals hydrological and ecological transformations from China’s South-to-North Water Diversion Project

The Middle Route of the South-to-North Water Diversion Project (MR-SNWDP) in China, as the largest inter-basin water transfer initiative in the world, has profoundly influenced the regional hydrology, ecology and climate of both the Water Source Areas (WSA) and Water Receiving Areas (WRA). This study aimed to comprehensively assess the long-term environmental impacts of the MR-SNWDP from 2004 to 2023, with particular emphasis on vegetation dynamics in response to both climatic and anthropogenic drivers. It addressed a critical knowledge gap regarding the spatially heterogeneous ecosystem responses to large-scale hydrological interventions under climate variability. Utilizing satellite-derived datasets including GRACE Terrestrial Water Storage Anomalies (TWSA) for hydrological variations and MODIS Normalized Difference Vegetation Index (NDVI) for vegetation activity, we combined trend analysis with attribution modeling to explore the spatiotemporal patterns of environmental change. The findings highlighted that the MR-SNWDP has significantly alleviated water shortages in the WRA by increasing surface water storage and reducing groundwater extraction. This shift in water accessibility promoted vegetation growth, particularly in cropland regions, by extending the growing season through earlier greening and delayed senescence. Climatic factors such as precipitation and temperature were the dominant positive drivers of NDVI, while anthropogenic stressors, including urban expansion and agricultural intensification, exerted negative effects. However, the influence of climatic factors on vegetation dynamics weakened in the WRA following the project’s implementation, while the impacts of human activities became more prominent. This trend was attributed to the long-term redistribution of water resources under the MR-SNWDP, which mitigated water scarcity and rendered vegetation growth less sensitive to climatic fluctuations. Furthermore, vegetation recovery contributed to regulating urban microclimate and mitigating the urban heat island effect, reflecting broader ecological benefits in the WRA. In contrast, the WSA experienced reduced vegetation activity and increased ecological vulnerability, emphasizing the need to balance inter-basin water transfers with local ecosystem sustainability.