Land subsidence poses a serious risk to the low-lying coastal city of Bangkok, Thailand; major flooding occurred there in 1983 and again in 2011. Extreme water pumping in the past led to subsidence rates of up to 120 mm year−1. Although water extraction is now controlled, maximum rates measured by levelling today are still up to 20 mm year−1. In this study, we apply interferometric synthetic aperture radar (InSAR) time-series analysis to study subsidence in Bangkok between October 2005 and March 2010. We validate the InSAR results, by comparing levelling rates and find good agreement between the two techniques. We detect approximately 300,000 coherent pixels overall, with an average density of 120 observations per km2. This is two orders of magnitude greater than the density of levelling benchmarks and reveals subsiding areas that are missed by the levelling network.
