422 I PART 3 I THE MEKONG EMERGENCY
[ Figure 9.11 ] Groundwater extraction scenarios and induced subsidence
(a) Groundwater extraction pathways for the XXIst century for different (non-)mitigation scenarios modelled in the VMD [ Minderhoud et al., 2020 ]. (b) Evolution of cumulative delta-average subsidence following the extraction pathways. Solid lines show the best-estimate model results, and the colours cover the range between the least and most conservative model. Time slices for 2050 and 2100 show the comparison of extraction-induced subsidence and sea level rise following IPCC SROCC scenarios [ Minderhoud et al., 2020 ].
In a naturally functioning delta, subsidence is counterbalanced by sediment deposition on the delta surface. However, there are no delta-wide data or estimates of present or future sediment deposition in the VMD. Therefore, it is not possible to create spatially explicit calculations including exact quantifications for sedimentation. Although unlikely in the pre-
sent situation, especially considering the strong decline in fluvial sediment reaching the delta, it can be assumed that natural compaction is being compensated by sediment deposition. Following this assumption, delta-wide future elevation was projected following projections of sea level rise and extractioninduced subsidence [ Figure 9.12 ].
