InSAR reveals coastal subsidence in the Pearl River Delta, China

The Pearl River Delta (PRD) is one of the most important economic regions with the highest population densities in China. With its dramatic increasing population and economy, hazards associated with land subsidence frequently occur here that amplify the negative effect of sea level rise. However, land subsidence has not been regularly measured in this region. Here, we use interferometric synthetic aperture radar (InSAR) to investigate the rate and extent of land subsidence in the PRD region. Assuming purely vertical displacements, multi-track interferograms from different viewing geometries are combined to estimate the linear rate map and time series at a higher resolution in time than is possible with a single track. The results show apparent subsidence along the coastal region of Shenzhen associated with rapid urban development in recent years. The average subsidence rate within 500 m of the coast is about 2.5 mm yr-1, and the maximum is up to about 6 mm yr-1 with respect to the central part of the city. Much of the land surface in the PRD is less than 2 m above mean sea level; high-precision geodetic measurements throughout the PRD region are therefore critical for conducting risk assessments, considering the rate of about 23 mm yr-1 of current global sea level rise.