Analysis of groundwater changes (2003-2020) in the North China Plain using geodetic measurements

Study region: North China Plain (NCP), China. Study focus: This paper investigates the spatiotemporal characteristics of groundwater storage (GWS) changes in the NCP during 2003-2020 using Gravity Recovery and Climate Experiment (GRACE) and Global Navigation Satellite System (GNSS) measurements with a focus on the subperiods separated by the implementation (December 2014) of the South-to-North Water Diversion Middle Route Project (MRP). New hydrological insights for the region: GRACE-derived results demonstrate that GWS depleted at rates of 1.66 +/- 0.17 cm/yr and 2.76 +/- 0.55 cm/yr for subperiods of 2003-2014 and 2015-2020, respectively, suggesting that GWS continued decreasing after the MRP. However, the spatial distribution of average monthly GWS shows an evident southwest-northeast band distribution, and the GWS depletion in the northwest has been alleviated compared with the southeast. The GNSS stations in the Beijing area show accelerated increasing rates of vertical displacements, while those in the plain areas of Hebei and Tianjin show continuous declining rates, implying that GWS in the Beijing area recovered faster after the MRP, while the GWS depletion in plain areas of Hebei and Tianjin continued. In addition, precipitation is the main driving factor to GWSvaribility during the whole study period, with grey correlation coefficients of 0.66-0.75. This strong correlation explains the significant reduction in GWS caused by the large precipitation deficit in 2019, which leads to a larger GWS depletion rate for the 2015-2020 period.