Objectives The North China Plain is one of the most important agricultural and industrial areas in China, however, long-term over-exploitation of groundwater has led to serious ground subsidence problems in the region. Tangshan City, as a typical representative of the region, has experienced significant surface subsidence due to over-exploitation of groundwater in the southern part of the city as a result of rapid economic development and population growth. The objective of this paper is to effectively monitor surface deformation and analyze its relationship with groundwater fluctuations.

Methods Sentinel-1 multi-temporal synthetic aperture radar (SAR) data were utilised for monitoring using the small baseline subset interferometric SAR technique. The main deformation modes of the southern part of Tangshan City between 2015 and 2021 were isolated by principal components analysis (PCA).

Results Spatial and temporal deformation characteristics of the southern part of Tangshan City were obtained. There are large-scale subsidence signals in coastal areas, mainly distributed in Ninghe-Hangu, Tanghai-Laoting, and Laoting-East, which coincide with the location of deep groundwater funnels. The maximum cumulative ground subsidence reaches 800 mm,PCA shows that there is a significant correlation between ground subsidence and groundwater exploitation in the study area. Overexploitation of groundwater leads to long-term linear deformation characteristics, with the explanatory components of linear deformation and its disturbance accounting for 95.88% and 1.91%, respectively. Periodic changes in water level lead to seasonal fluctuations, with the explanatory component accounting for 0.61%. The seasonal fluctuations are as follows: During the spring drought period, the amount of groundwater extraction increases due to irrigation demand, and the subsidence rate accelerates; The summer precipitation replenishment partially slows down the subsidence rate. And the analysis shows that there is a certain lag response of ground subsidence to groundwater level, with an interval of about 15 days. In addition, the study observed localised subsidence triggered by human activities such as mining and urban expansion.

Conclusions The study is important for urban ground deformation monitoring and urban development governance.