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

根据政府间气候变化专门委员会最新的温和预测，全球平均海平面预计到2100年将上升0.32-1.01米。大型三角洲容易出现异常的海平面上升率（SLR），其中等水位线和压实超过沉积。在未充分研究的伊洛瓦迪三角洲（缅甸），相对SLR导致最低地区被淹没，而热带气旋引起的季风洪水和风暴潮对三角洲更大的部分构成威胁。最近事件的灾难性影响表明，对伊洛瓦迪三角洲高强度灾害的了解有限，造成了后果，在那里，巨大的灾害风险与高风险程度和有限的复原能力并存。因此，更好地了解海平面，洪水和社会活动之间的因果关系，作为未来减灾和风险治理战略的基础，已经成为2019年批准的初始项目的目标。尽管2019冠状病毒病及2021年2月缅甸政变严重阻碍了项目的实施，导致实地工作无法进行，但通过应用遥感技术，该项目在评估伊洛瓦迪三角洲的洪水灾害、脆弱性及风险方面取得了重要成果。然而，制定可持续的缓解战略，未来的洪水风险，进一步深入了解相对SLR和有效的适应战略的驱动因素是必不可少的。这是我们后续提案的重点，该提案将首次系统地调查地面沉降对当地SLR的贡献，并针对三角洲的减灾战略。迄今为止，伊洛瓦迪三角洲的地面沉降仅在当地进行了评估，对相对SLR的贡献是基于模糊的估计，尽管它构成了自然系统和社会活动之间的重要联系。需要关于地面沉降的空间和时间模式的数据，以了解社会与减轻或可能产生的灾害风险之间的相互作用。这些研究结果为风险敏感的适应战略提供了基础，这些战略将通过有当地和国际专家参与的以内罗毕为基础的规划来制定，目的是共同创造知识。这将有助于制定应对战略，以便为子孙后代保护三角洲的住区和经济功能。因此，后续提案旨在通过以下方式进一步改善伊洛瓦迪三角洲洪水风险的评估和缓解：（i）提供关于地面沉降的新的、独特的数据，作为相对SLR的主要驱动因素;（ii）调查相对SLR和人类活动之间的相互依赖关系;以及（iii）为未来洪水风险的可持续管理制定动态适应途径。从确定SLR驱动因素到制定适应途径的整体方法可以作为一种模式，也适用于其他特大三角洲。

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.