Rising sea and sinking land: Determining spatially resolved subsidence rates for the Ayeyarwady Delta (Myanmar) and developing dynamic adaptation scenarios for the increased risk of flooding

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According to the latest moderate IPCC projections, global mean sea level is expected to rise by 0.32–1.01 m until 2100. Large deltas are prone to exceptional rates of sea-level rise (SLR) where isostasy and compaction exceed sedimentation. In the understudied Ayeyarwady Delta (Myanmar), relative SLR leads to drowning of the lowest areas, while monsoon floods and storm surges induced by tropical cyclones are a threat to much larger parts of the delta. The catastrophic impacts of recent events demonstrated the consequences of limited knowledge concerning high-magnitude hazards in the Ayeyarwady Delta, where great disaster risk meets high levels of exposure and limited resilience capacity. Therefore, an improved understanding of causalities between sea levels, flooding and societal activities as the basis for future strategies of mitigation and risk governance was already targeted by the initial project granted in 2019. Although the implementation was considerably hampered by Covid-19 and the coup d'état in Myanmar in February 2021, which has been making fieldwork impossible, by applying remote sensing the granted project made important achievements regarding the assessment of flood hazard, vulnerability and risk in the Ayeyarwady Delta. However, to develop sustainable mitigation strategies for future flood risk, further insights into the driving factors of relative SLR and effective adaptation strategies are essential. This is the focus of our follow-up proposal, which for the first time will systematically investigate the contribution of land subsidence to local SLR and target disaster risk reduction strategies in the delta. As yet, land subsidence in the Ayeyarwady Delta has been assessed only locally and is contribution to relative SLR is based on vague estimates, although it constitutes a crucial link between the natural system and societal activities. Data on spatial and temporal patterns of land subsidence are needed to understand interactions between society and the mitigation or potential creation of disaster risks. These findings provide the basis for risk-sensitive adaptation strategies, which will be developed through scenario-based planning involving local and international experts, aiming at the co-creation of knowledge. This will contribute to the development of coping strategies in order to preserve settlements and economic functions of the delta for future generations. Consequently, the follow-up proposal aims to further improve the assessment and mitigation of flood risk in the Ayeyarwady Delta by (i) providing new, unique data on land subsidence as a main driver of relative SLR; (ii) investigating the interdependencies between relative SLR and human activities; and (iii) developing dynamic adaptive pathways for sustainable management of future flood risk. The holistic approach from the identification of SLR drivers to the development of adaptation pathways can serve as a model that is also applicable to other megadeltas.