Sub-regional groundwater storage recovery in North China Plain after the South-to-North water diversion project

The South-to-North water diversion Middle Route Project (MRP) is expected to alleviate the long-term groundwater storage (GWS) depletion in North China Plain (NCP) after the beginning of its operation in December 2014. This study aims to investigate the effect of MRP on GWS by comparing GWS changes before (2003–2014) and after (2015–2018) the MRP operation. The analysis was conducted by using groundwater level data from 617 wells in NCP, and then evaluated against satellite-based water storage data from Gravity Recovery and Climate Experiment (GRACE) and its Follow-On missions. On average in NCP, a decreasing trend of −19.1 ± 5.1 mm/yr was seen in GWS based on well observations during 2003–2014, but a recovery trend of +1.8 ± 0.7 mm/yr was found during 2015–2018. The GWS recovery was most prominent in subregions where groundwater over-utilization had occurred in NCP. GRACE exhibited the capacity to detect the regional GWS depletion during 2003–2014, but difficult to distinguish the sub-regional GWS recovery during 2015–2018. The potential causes for GWS recovery were found to be complicated, not only caused by the reduction of groundwater pumping as accelerated by MRP-diverted water, but also the increasing precipitation recharge of aquifers and the enhanced management of groundwater system. The findings highlight that GWS in NCP has started a gradual transition from unsustainable depletion to sub-regional recovery as benefit from the MRP water diversion.