Wide-area deformation surveying and Groundwater Volume Loss assessment in the North China Plain by Multi-track InSAR Observations and mechanical models

The long-term over-extraction of groundwater in the North China Plain(NCP) has led to disasters such as ground subsidence, ground fissures, and seawater intrusion. These have posed serious threats to infrastructure, aquifer systems, and the ecological environment. By establishing a functional model of surface deformation and groundwater changes, we can enhance our understanding of the mechanisms behind ground subsidence and quantitatively assess how groundwater storage evolves under the dual influences of human activities and natural processes. InSAR (Interferometric Synthetic Aperture Radar) has proven to be the most effective tool for long-term、wide-area ground deformation monitoring and underground hydrological parameter inversion. Considering the characteristics of ground subsidence such as long-term, progressive, and wide distribution, in this study, eight stacks of 1496 Sentinel-1A/1B SAR scenes spanning from 2017 to 2023 were acquired in ascending mode along tracks T40 and T142. Through methods like (InSAR) time series analysis method、phase unwrapping correction and spatio-temporal smoothing fitting, we obtained a long-time-series high-precision LOS deformation field for the NCP. Secondly, by introducing the spatial domain network adjustment method, we can implement joint adjustment and correction of wide-area multi-map results to obtain a unified spatio-temporal reference for the NCP's wide-area InSAR vertical ground deformation field. Finally, we use the InSAR-VSM model based on elastic half-space and the one-dimensional poroelastic model considering elastic unloading to obtain independent quantitative estimates of groundwater loss in NCP. For the first time, we have reduced the spatial resolution of groundwater reserves inversion in the NCP from hundreds of kilometers to several kilometers, breaking through the bottleneck of insufficient spatial resolution in groundwater hydrological research. By integrating the South-to-North Water Diversion Project, groundwater extraction policies in the NCP, meteorological datasets, and groundwater level data, we have found that there are significant differences in the response mechanisms of groundwater and land subsidence between piedmont plains and flood plains in the NCP. Our data and results have enhanced our understanding of changes in groundwater storage in the North China Plain and provide scientific support for scientifically managing groundwater resources and carrying out related work on preventing and mitigating ground subsidence disasters.