The Divergent Changes in Surface Water Area after the South-to-North Water Diversion Project in China

Water scarcity is a significant challenge in China, and the South-to-North Water Diversion Project (SNWDP) aims to address the water deficit in the northern region. This study analyses Landsat 5/7/8 remote sensing imagery from 2001 to 2020 on the Google Earth Engine (GEE) cloud platform to assess the impact of the SNWDP on surface water bodies in water-receiving areas. Moreover, by integrating MODIS evapotranspiration data and ERA5 meteorological reanalysis data, this study comprehensively assesses the SNWDP's contribution to varied surface water body changes. Using an improved multi-temporal water frequency method, this study extracts max, seasonal, and year-long water surface areas. The results reveal that Beijing and Henan provinces have experienced significant increases in water surface areas post-SNWDP, with their max water surface area growing at a rate of 10.42 km2/yr and 33.49 km2/year, respectively. However, water surface areas in several provinces, especially those along the east route, were not observed to increase. The spatially detailed Mann-Kendall test indicates that the expansion of year-long water bodies is mostly concentrated near the central route project, revealing spatial heterogeneity in the water replenishment effect. Cropland and impervious surfaces are the main contributors to transfers in and out of water bodies. Meteorological and water use factors for spatial variations in water changes are also identified. These findings provide insights into the varied hydrological consequences of the SNWDP and contribute to the evaluation and management of similar large-scale water diversion projects around the world.