Drought‐Induced Land Subsidence in the Mekong Delta, Vietnam: Insights From SAR Interferometry

The Mekong Delta has been affected by land subsidence for decades, increasing its vulnerability to coastal erosion and floodings. Here we show, based on subsidence time series from SAR Interferometry, that severe droughts can significantly intensify the subsidence. We measured a subsidence of up to 7 cm in few months during a drought in 2020, which was compensated by uplift in the following rainy season in some but not all regions. The magnitude of the drought-induced subsidence was spatially correlated with specific surface water management and land use zones, with the largest impact in rain-fed, rice growing regions. We argue that the uncompensated surface drop in two regions, reaching up to 3.5 cm, was caused by inelastic deformation. Such irreversible subsidence has a major impact on the delta's future elevation, especially under the assumption that the frequency of droughts will increase under climate change and an increasing water demand.