Revealing the lagged relationship between groundwater changes and land subsidence in Tianjin based on GRACE and InSAR observations

Tianjin has long been plagued by land subsidence, which is primarily caused by groundwater over-exploitation and poses major threats to urban construction, economic development, and infrastructure safety. This study aims to explore the relationship between groundwater storage (GWS) changes and land subsidence in Tianjin by combining GRACE and InSAR technologies. To clarify this relationship macroscopically, GRACE and GLDAS data were used to analyze GWS changes in the study area from January 2023 to February 2025, while PS-InSAR was applied to obtain concurrent land subsidence information. Time-lagged cross-correlation analysis was introduced to quantify the correlation and lag time between GWS changes and land subsidence time series. Results showed: (1) GWS was positive in most areas (maximum annual rate 59.13 mm/yr, concentrated in east-central Jinghai, south-central Xiqing, Jinnan and central Binhai New Area), decreasing from the center to north and south, with a significant decline (-9.22 mm/yr) in northern Binhai New Area; severe land subsidence showed a “peripheral aggregation” pattern, with 4 contiguous zones, 7 funnels and a max rate of 67.62 mm/yr (near Yangjiapo Town, Binhai New Area); (2) The cross-correlation coefficient between GWS changes and land subsidence ranged from 0.257 to 0.882 (0.542–0.853, 0.431–0.826, 0.257–0.882, 0.538–0.846 for Zones I-IV respectively), and land subsidence lagged GWS changes by 41–263 days overall. This study confirms the link and lag effect between GWS and land subsidence in Tianjin, providing scientific guidance for subsidence prevention and early warning.