Unravelling the influencing hydrogeological factors contributing to land subsidence in the Tianjin Plain of China using a multi-scale geographically weighted regression model and monitoring data

The establishment of a quantitative relationship between land subsidence and its influencing factors is a crucial task in developing prevention strategies of land subsidence in specific areas. In this study we examined the dynamic patterns of land subsidence before and after establishing the South-to-North Water Division Project (SNWDP) in the Tianjin Plain (TJP) that aims to reduce groundwater extractions in certain areas. Statistical analyses were used to determine the key attributing factors contributing to land subsidence that were subsequently used to derive the so-called ‘critical water level of land subsidence’(CWLS), which were used to manage groundwater extractions with the objective of minimizing further land subsidence. The main results obtained were as follows: under the influence of the SNWDP, the groundwater level in the TJP stopped declining and the water level rose in most areas. The area of ‘strong’ subsidence, defined as the area with a subsidence rate greater than 50 mm a −1 , decreased from 16.0% before the SNWDP to 2.5% after. The results of the multi-scale geographically weighted regression (MGWR) model revealed that groundwater drawdown in the second and third confined aquifer was the main contributor to the areas classified as ‘strong’ and ‘medium’ land subsidence areas. Following the reduction in groundwater extractions, the behaviour of surface deformation can be grouped into two categories: first, a rebound in surface elevation; and, second, continuous compression with a lower subsidence rate. The first mode occurs mainly in the area of ‘medium’ and ‘weak’ subsidence, and the second mode occurs mainly in the ‘strong’ subsidence area. Supplementary material : The result of the MGWR model is available at https://doi.org/10.6084/m9.figshare.c.7103611