Causal effects of the south-to-north water diversion project on groundwater restoration in Beijing

Abstract

The South-to-North Water Diversion Project (SNWDP), China’s largest inter-basin water transfer scheme, has supplied Beijing with over 10 billion m3 since Central Route operations commenced in December 2014. This study exploits the 2014 commissioning as a policy discontinuity and applies a sharp Regression Discontinuity Design (RDD), complemented by water balance analysis, within a quasi-experimental framework. Using a 45-year annual time series (1980-2024) of mean groundwater depth and cone of depression area across the Beijing Plain, we evaluate the SNWDP’s ecological restoration effects. Linear RDD estimates reveal a statistically significant discontinuity at the 2014/2015 threshold: +4.16 m in mean groundwater depth (p<0.001) and −225.9 km2 in cone of depression area (p<0.05). Placebo tests, bandwidth sensitivity analyses, and covariate robustness checks confirm these estimates. Water balance calculations indicate a cumulative groundwater extraction displacement of 5.59 billion m3 (mean displacement rate: 59.1%) and cumulative storage recovery of approximately 10.19 billion m3 (overall recharge efficiency: 42.4%) over 2015–2024. The results trace a clear causal pathway—supply substitution → reduced extraction → water-table recovery → depression cone contraction—and provide a transferable methodological framework for assessing the ecological impacts of large-scale inter-basin water transfer projects.