Inferring decelerated land subsidence and groundwater storage dynamics in Tianjin-Langfang using Sentinel-1 InSAR

To meet the growing demand for socioeconomic development, a large amount of groundwater is extracted from confined aquifers worldwide. The North China Plain has experienced considerable groundwater depletion and subsidence during the past six decades. In this study, we use Sentinel-1A/B SAR images from 2015 to 2020 to map the ground subsidence of the Tianjin-Langfang area. Three subsiding zones centered at Guangyang, Wuqing-Bazhou, and Jinghai are identified with maximum subsidence rates of 98.1, 121.8, and 104.7 mm/yr. Seasonal and long-term signals are separated from time series subsidence and hydraulic measurements using continuous wavelet transform to retrieve aquifer parameters. The long-term subsidence, which fits well with an exponential decaying model, remarkably slows down in our study area. The elastic skeletal storage coefficients range between 0.52x10(-3) and 9.66x10(-3). We then retrieve the spatial-temporal variations of total groundwater storage, recoverable groundwater storage, and irreversible groundwater storage. Groundwater storage depletion rates are apparently reducing, which benefits from the operation of the South-to-North Water Transfer Project and local groundwater management practices.