Remote sensing insights into drought induced land subsidence in the Vietnamese Mekong Delta

The Vietnamese Mekong Delta has been affected by environmental challenges for several decades, including land subsidence and an increased frequency of droughts. While the former leads to a growing vulnerability to coastal erosion, floodings and permanent inundation, the latter has led to considerable crop failures in the past. In this work, we use InSAR-derived subsidence time series and remote sensing based meteorological information to study seasonal vertical displacements in the Mekong Delta, which align with the distinct dry and wet seasons in most locations and overlay a background subsidence trend. We show that a drought in 2020 lead to a significant increase in the seasonal subsidence in parts of the delta. The magnitude of this drought-induced subsidence, which was up to several centimeters in a few months, was related to the surface water management and land use. It was compensated by uplift in the following rainy season in several but not all regions. We argue that the observed surface drop in some regions was caused by inelastic deformation in the aquifer-aquitard system and/or the shallow soil. The findings of this work highlight the importance of further research on drought-induced subsidence in the Mekong Delta, especially under the assumption that the frequency of droughts might further increase in the future due to climate change and an increasing water demand.