# Two Decades of Land Subsidence in Tianjin, China, Measured with Multi-Temporal InSAR Observations

## TL;DR

This study tracks 20 years of land subsidence in Tianjin, China, using satellite data to show how subsidence patterns shifted over time due to groundwater use and urban development.

## Contribution

The study provides a long-term spatiotemporal analysis of land subsidence in Tianjin using multi-source SAR data and a model-based time-series fitting approach.

## Key findings

- Subsidence rates in inland districts like Wuqing and Beichen exceeded 50 mm/yr from 2003–2010.
- After 2017, subsidence shifted to localized areas in the Binhai New Area, especially near Dongjiang Port and Fuzhuang.
- Subsidence patterns correlate with groundwater use and urban construction phases.

## Abstract

Land subsidence poses a persistent challenge to Tianjin, a major coastal city in China, with implications for urban infrastructure and sustainable development. This study examines the spatiotemporal evolution of ground subsidence in Tianjin from 2003 to 2024 using multi-source SAR observations from Envisat ASAR (C-band), ALOS PALSAR (L-band), and Sentinel-1 (C-band). Surface deformation was derived using SBAS-InSAR with atmospheric phase correction. Due to limitations in data availability, SAR observations are temporally discontinuous; therefore, the long-term subsidence evolution was reconstructed by integrating multi-sensor deformation rates through a model-based time-series fitting approach. The results show pronounced subsidence during 2003–2010 in inland districts such as Wuqing, Beichen, Jinnan, and Jinghai, with maximum rates exceeding 50 mm/yr. After 2017, regional subsidence rates generally declined, while localized deformation became increasingly concentrated in coastal reclamation areas of the Binhai New Area, particularly around Dongjiang Port and Fuzhuang. Spatial and temporal patterns of subsidence exhibit clear correspondence with changes in groundwater use intensity and phases of urban construction and land reclamation. These observations suggest a transition in dominant subsidence controls over time. The results provide a long-term observational perspective on subsidence evolution in Tianjin and offer a geospatial basis for land-use planning and infrastructure risk assessment in coastal cities.