Trend changes of terrestrial water in the North China Plain and Shaanxi-Gansu region inferred from vertical GNSS data

Widespread subsidence in the North China Plain (NCP) and Shaanxi-Gansu region has been a concern of potential hazards. Investigating the underlying factors contributing to this subsidence is essential for effective hazard mitigation policies. In this study, we use GNSS data to derive the vertical velocity difference between the periods of 2011—2014 and 2015—2018. The results feature a general decrease in subsidence rates across the NCP, except in Cangzhou that exhibits a notable increase in subsidence at a rate of 15.4 mm·a−1. In the Shaanxi-Gansu region, subsidence rates are much lower, ranging from -2 to 2 mm·a−1, but Xi′an stands out with a significant increase of 4.5 mm·a−1. To further explore the mechanism of subsidence, we analyze the vertical GNSS data based on the elastic loading theory to reveal potential corresponding trend changes in terrestrial water (TW). The results indicate that the GNSS-derived TW trend changes in the study area are consistent with statistical and well data, indicating a positive effect on the groundwater level recovery in the NCP due to the central South-to-North Water Diversion (SNWD) project, but the decrease in groundwater level in Xi′an is probably caused by urban infrastructure activities. This study offers insights for policymakers to address land subsidence and manage water resources.