Present Estimations of Subsidence Induced by Sediment Isostasy and Glacial Isostatic Adjustment in the Ayeyarwady Delta (Myanmar)

Abstract Estimating relative sea level rise, which measures changes in sea level compared to the land where people live, is crucial for the Ayeyarwady Delta, home to 15 million residents on this low‐lying delta. Like many large deltas, the Ayeyarwady Delta should experience subsidence from its own weight, worsening the effects of sea level rise. Despite the potential impact of this phenomenon, no studies have quantified its magnitude in this area. To address this gap, we model isostatically induced vertical land movement (II‐VLM), capturing the viscoelastic response of the solid Earth to surface mass changes, including both glacio‐hydrostatic and sediment mass changes since the Last Glacial Maximum (LGM). Thus, we quantify its contribution to the present relative sea level change. The modeling is conducted under the hypothesis of a one‐dimensional radially symmetric Earth structure, integrating stratigraphic observations to provide insights into the history of sedimentation. We explore uncertainties to provide a range of subsidence induced by ocean rise since the LGM and by the 250 Mt/yr of sediment trapped during the Holocene in this region. Results indicate II‐VLM rates of 0.7–1.5 mm/yr near the mouth of the Ayeyarwady River. While other processes, such as compaction and tectonics, may dominate subsidence, our findings suggest that II‐VLM is significant for Indian Ocean delta plains and must be considered in regional flooding hazard assessments and mitigation strategies.