Spatial Variability of Relative Sea-Level Rise in Tianjin, China: Insight From InSAR, GPS, and Tide-Gauge Observations

Abstract

The Tianjin coastal region in Bohai Bay, Northern China, is increasingly affected by storm-surge flooding which is exacerbated by anthropogenic land subsidence and global sealevel rise (SLR). We use a combination of InSAR (Synthetic Aperture Radar Interferometry), CGPS (continuous GPS), and tide-gauge observations to evaluate the spatial variability of relative SLR (RSLR) along the coastline of Tianjin. Land motion obtained by integration of two tracks of Sentinel-1 SAR images and nineteen CGPS stations shows that the recent land subsidence in Tianjin downtown is less than 8 mm/yr, which has significantly decreased with respect to the last 50 years (up to 110 mm/yr in the 1980s). This might benefit from the South-to-North Water Transfer Project which has provided more than 1.8 billion cubic meters of water for Tianjin city since 2014 and reduced groundwater consumption. However, subsidence centers have shifted to suburbs, especially along the coastline dominated by reclaimed harbors and aquaculture industry, with localized subsidence up to 170 mm/yr. Combining InSAR observations with sea level records from tide-gauge stations reveals spatial variability of RSLR along the coastline. We find that, in the aquaculture zones along the coastline, the rates of land subsidence are as high as 82 mm/yr due to groundwater extraction for fisheries, which subsequently cause local sea levels to rise nearly 30 times faster than the global average. New insights into land subsidence and local sea-level rise could help the country's regulators to make decisions on ensuring the sustainable development of the coastal aquaculture industry.

Short- to Medium-Term Sea Surface Height Prediction in the Bohai Sea Using an Optimized Simple Recurrent Unit Deep Network

“…In the last 10 years, the average sealevel of China's coastal areas has been at a high level in the past 40 years, being about 100 mm higher than the average sea-level in 1980-1989. Due to the shallow water of the Bohai Sea (average 18 m), the rate of rise of the sea-level in this area for 1980-2019 was 3.7 mm/a. It is estimated that, in the next 30 years, the sea-level of the Bohai Sea will rise by 55-180 mm (Tang et al, 2021).…”

“…The factors affecting sea-level change include melting glacial ice, precipitation, evaporation, runoff, and other seawater exchange processes, as well as changes in seawater density due to changes in temperature or salinity (Jeon et al, 2021). These factors are classified as spatial effects (Tang et al, 2021). It was reported (Guo et al, 2015) that the seasonal variation and spatial distribution of SSHA were related to the changes in the volume of seawater and the effect of differences in temperature, which are due to changes in the onset of the monsoon and the seawater temperature, respectively.…”

Understanding the Spatial-Temporal Characteristics of Land Subsidence in Shenzhen under Rapid Urbanization Based on MT-InSAR

“…However, the current situation of land subsidence in China deteriorates with urbanization progress, especially in cities with rapid urbanization. Additionally, in addition to land subsidence, other secondary disasters, such as sinkholes [3], urban flooding [4], infrastructure damage [5], and seawater intrusion in coastal areas [6,7], can threaten people's lives and the normal operation of cities. Specific to the city of Shenzhen, it has undergone tremendous urbanization with the rapid development of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) in the past few decades [8].…”

Research on time series InSAR monitoring method for multiple types of surface deformation in mining area

“…The Interferometric Synthetic Aperture Radar (InSAR) technology proposed in the 1970s is a newly developed active microwave remote sensing earth observation technology in recent years (Bhattacharya and Mukherjee 2017;Moreira et al 2013;Mastro et al 2020), which can continuously monitor the mine area surface displacement with the help of image data obtained during the transit of SAR satellites. After recent decades of development, today's InSAR mainly include Digital Elevation Model (DEM) production (Zhang, Wang, and Chen 2012), differential InSAR (D-InSAR) (Wang et al 2009) and time-series InSAR (TS-InSAR) deformation monitoring (Fan, Lu, and Yao 2018).InSAR deformation monitoring has been widely used to monitor surface deformation, such as mining (Yang et al 2020;Sui, Ma, and Chen 2020), landslides (Castaneda et al 2009), volcanic eruptions (Olivier et al 2019;Comerci et al 2015), glacial movements (Zhou et al 2011;Li et al 2009), spatial changes in sea level (Tang et al 2021), and urban ground subsidence (Chen et al 2021;Ding et al 2021;Li et al 2016).…”