Accelerated Land Subsidence and Complex Temporal Variations in Newly Developed Areas in Dhaka, Bangladesh, Observed by InSAR

Dhaka is emerging as one of the fastest-growing megacities in the world, having more than 20 million inhabitants. The city is facing environmental challenges due to rapid industrialization, including increased pollution in surface water. As a result, the city heavily relies on groundwater for drinking and industrial purposes, causing adverse effects including land subsidence. However, limited studies have been conducted to monitor this phenomenon in Dhaka. This study utilizes interferometric synthetic aperture radar (InSAR) data acquired by ALOS between 2007 and 2011 and Sentinel-1 between 2015 and 2022 to measure land subsidence in Dhaka. Widespread of >1 cm/yr subsidence rate is observed during both periods, and the spatial variation is likely related to variations in subsurface soil properties and groundwater consumption. Comparison of in situ groundwater level (GWL) and land subsidence time series exhibits moderate to strong correlations. An F-test indicates that the recent land subsidence in Dhaka can be characterized by linear or parabolic functions for most areas. Comparison of velocity maps derived from ALOS and Sentinel-1 data highlights several hotspots with accelerated land subsidence, notably an under-construction residential area named Jolshiri Abashon. This area is situated in a former wetland, where the subsidence rate has more than doubled between the two observational periods (from ~2.5 cm/yr to >5 cm/yr). InSAR-derived displacement time series after the beginning of construction (started in 2012) can be characterized by an exponential decay model. The fast subsidence rate and the city’s high susceptibility to flood warrant heightened monitoring.