Philip S. J. Minderhoud , Artur Guzy, Selena Baldan, Riccardo Xotta, Bente R. Lexmond, Claudia Zoccarato, Pietro Teatini

The Mekong delta, one of the largest deltas in the world, is densely populated and important for food production. As the delta plain is lowly elevated, less than a meter on average above local sea level, it is vulnerable to sea-level rise and land subsidence. The delta experiences high rates of natural compaction at its coast) while human activities associated with land-use change , urbanisation and intensified groundwater exploitation are accelerating subsidence further. At present the delta experiences high rates of land subsidence, with a delta-wide average rate exceeding 10 mm/yr and local rates as high as 60 mm/yr. As a result, the relative sea-level rise in the Mekong delta is dominated by land subsidence and forms an existential threat to the delta.
Deltaic subsidence is the cumulative effect of various drivers and processes in the subsurface, that can be both of natural and anthropogenic origin. As a result, subsidence can be both spatially and temporally highly variable within a delta. Subsidence caused by natural processes is unavoidable and can only be countered by adaptation, such as managed sedimentation strategies to build elevation through sediment deposition, while human-induced subsidence can be reduced or mitigated following a proper strategy.
In recent years the number of studies on subsidence in the Mekong delta has increased considerably, from direct measurements at a few locations in the delta using relative surface elevation tables and dedicated subsidence monitoring stations delta-wide InSAR estimates. These estimates, combined with land-use change detection, revealed the spatial-temporal evolution and land-use change impacts on subsidence and detailed analyses of differential, depth-dependent subsidence in urban areas in the delta. Two different numerical models were created targeting distinct subsidence processes: 1) groundwater extraction-induced aquifer-system compaction, consequently used to create future elevation projection under different extraction scenarios, and 2) natural compaction of shallow sediments following Holocene delta progradation. This contribution provides an overview of past and ongoing numerical advances in subsidence modelling in the Mekong delta and provides an outlook for future work.