Spatial Variability of Relative Sea-Level Rise in Tianjin, China: Insight From InSAR, GPS, and Tide-Gauge Observations
Published in March 03, 2021
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 sea-level rise (SLR). We use a combination of synthetic aperture radar interferometry (InSAR), continuous GPS (CGPS), and tide-gauge observations to evaluate the spatial variability of relative SLR (RSLR) along the coastline of Tianjin. Land motion obtained by integration of 2 tracks of Sentinel-1 SAR images and 19 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 SLR could help the country’s regulators to make decisions on ensuring the sustainable development of the coastal aquaculture industry.
位于中国北方渤海湾的天津沿海地区，正日益受到风暴潮洪水的影响，这一情况由于人为土地沉降和全球海平面上升（SLR）而加剧。我们结合合成孔径雷达干涉测量（InSAR）、连续GPS（CGPS）和潮位计观测，评估天津沿海地区相对海平面上升（RSLR）的空间变化。通过整合两条Sentinel-1 SAR影像轨道和19个CGPS站点获得的地面运动数据显示，天津市区近期的土地沉降速率不到8毫米/年，与过去50年相比显著减少（20世纪80年代最高曾达到110毫米/年）。这可能得益于自2014年以来南水北调工程为天津市提供超过18亿立方米的水资源，减少了地下水消耗。然而，沉降中心已转移到郊区，特别是在由填海造地和水产养殖业主导的沿海地区，局部沉降速率达到170毫米/年。将InSAR观测与潮位计站的海平面记录结合，揭示了沿海地区RSLR的空间变化。我们发现，在沿海的水产养殖区，由于抽取地下水用于渔业，土地沉降速率高达82毫米/年，导致当地海平面上升的速度几乎是全球平均速度的30倍。关于土地沉降和局部海平面上升的新见解可帮助国家监管机构做出决策，以确保沿海水产养殖业的可持续发展。