Faster and More Effective Recovery of Surface Water in the Water-Receiving Area of the Middle Route South-to-North Water Diversion Project

Abstract

Large-scale inter-basin water transfer projects have been implemented to mitigate the uneven spatial distribution of water resources at regional and national scales. Assessing the effectiveness and impacts of these projects remains a substantial challenge. The Middle Route South-to-North Water Diversion Project (MR-SNWDP) in China has reversed the declining trend of groundwater storage (GWS) in parts of the water-receiving area. However, the effects of the project on surface water quantity and quality, particularly in lakes and reservoirs, remain unclear. Here, a novel framework was developed to quantify the impact of the MR-SNWDP on surface water by integrating altimetry, gravity, and optical remote sensing satellite data. Following the implementation of the MR-SNWDP in December 2014, surface water volume increased significantly. In the project-affected zone, the increase averaged over 0.9 km3 per year, equivalent to approximately 13.5% of the annual water diversion and 19 times that in the unaffected zone. Surface water transparency, a proxy for surface water quality, also improved in most lakes, with a significant positive correlation between transparency and volume increase in the affected zone. Water balance analysis indicated that the declining trend of GWS reversed in 2020, five years after the recovery of surface water. Our findings suggest that surface water recovered more rapidly and effectively than groundwater in the water-receiving area of the MR-SNWDP, highlighting the positive effects of transboundary water diversion projects on the quantity and quality of surface water.