Ecological water replenishment effects on groundwater recovery in the largest shallow groundwater depression cone of the North China Plain.

The North China Plain is among the world’s most severely groundwater-overexploited regions. Since 2018, large-scale ecological water replenishment (EWR) has been applied, yet its long-term impacts on groundwater dynamics and efficient EWR strategies remain poorly understood, particularly in the Shijiazhuang Plain, which hosts the largest shallow groundwater depression cone in the region. In this study, the coupled surface–groundwater model MODCYCLE was applied to investigate these issues in the Shijiazhuang Plain. Results reveal that large-scale EWR has effectively reversed groundwater depletion, recovering the average groundwater table by 1.96 m and storage by 1.76 billion m3 by 2022. Contributions were dominated by EWR from the Hutuo River (82.5%), followed by the Sha-Zhulong River (12%) and other Rivers (5.5%), with significant recovery (> 0.5 m, > 50,000 m3/km2) extending approximately 24.5 km, 12.5 km, and 5.5 km from these rivers. The highest-recovery zones were mainly in the middle and lower reaches of the EWR rivers. Our findings highlight that, due to its favorable infiltration path length and groundwater flow conditions, the Hutuo River should serve as the primary EWR channel, with stable, moderate flows rather than the “greater is better” approach, to achieve both efficient groundwater storage recovery and widespread groundwater table recovery. Optimal flows of 14.64 m3/s during droughts and ≥ 8.4 m3/s under normal precipitation efficiently mitigate and reverse groundwater depletion, respectively. This study provides scientific support for the continued fight against groundwater overexploitation in the North China Plain and offers insights for optimizing EWR strategies to efficiently recover groundwater in globally overexploited aquifers.