Comparison of GRACE/GRACE-FO Spherical Harmonic Coefficient and Mascon Products in Explaining the Influence of South-to-North Water Transfer Project on Water Reserves in the North China Plain

Abstract

The extent to which the South-to-North Water Transfer Project has influenced the trend in water storage deficit in the North China Plain since its official opening in late 2014 has not been systematically assessed. We evaluated the changes in terrestrial water storage (TWS) in the North China Plain based on the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-on (GRACE-FO) long-term gravity satellite observations from 2002 to 2022, using spherical harmonic (SH) solutions from the Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL), and Mass Concentration (Mascon) solutions from CSR, Goddard Space Flight Center (GSFC), JPL, and compared with the South-to-North Water Transfer water supply (13.91 Gt/a). The CSR-SH solution that best matched the water supply was selected, and it was found that the rate of change in TWS in the North China Plain from 2002 to 2015 was (−8.48 ± 1.87) Gt/a, and the rate of change from 2015 to 2019 increased significantly to (5.44 ± 4.87) Gt/a, indicating that the TWS in the plain changed from deficit to gain. The South-to-North Water Transfer Project has played a positive role in significantly improving the water stress situation in North China. Simultaneously, by comparing the inversions of six time-varying gravity field models (CSR-SH, GFZ-SH, JPL-SH, CSR-Mascon, GSFC-Mascon, and JPL-Mascon) with the South-to-North Water Transfer water supply and measured groundwater well data, and by calculating the uncertainty using the ‘three-cornered hat method’ (TCH), a comprehensive comparison is made to conclude that the CSR-SH model is most effective with a minimum difference of 0.01 Gt/a from the annual water supply, a minimum difference of 0.04 Gt/a from the measured well data, and a small uncertainty of 3.04 cm. This study reveals the important impact of the South-to-North Water Transfer Project on TWS in the North China Plain, which is of reference value for water resource management decisions in China.