The resilience and sustainability of the Mekong delta to changes in water and sediment fluxes (RAMESES)

世界上最大的33个三角洲正在被相对海平面上升淹没，结果是迅速失去了土地。这一过程还加剧了这些环境中的洪水风险，使许多大城市、关键基础设施和全球超过5亿人面临风险。这些问题对整个南亚和东南亚的三角洲来说最为严重，估计到2100年，那里将失去20%的土地。这些风险是巨大的。例如，2011年亚洲季风期间的洪水造成估计2000人死亡，并在整个东南亚造成约450亿美元的经济损失。此外，这些三角洲及其生态系统服务为快速增长的人口的区域粮食安全奠定了基础。因此，迫切需要改进对这些三角洲环境中相对海平面上升和洪水风险动态背后的过程的一般性理解，直至未来。最近在我们对三角洲地貌动力学和演化的许多方面的理解方面取得了重大进展。这包括关于分流河道水流过程、分叉稳定性和沙洲动力学的工作，以及潮汐回水效应对较长期河道水力和泥沙动力学的深刻影响。然而，尽管取得了这一进展，但围绕以下方面的影响仍存在重大不确定性：i)海平面上升迫使上游回水迁移对三角洲分叉稳定性的影响；ii)输沙能力下降和水文变异性增加对分流河道稳定性的影响；iii)河道与三角洲表面之间的连通性对沉积物的路线、扩散和捕获的影响。这些不确定性中的每一个都是必须解决的关键知识差距，以便有效地管理三角洲、减轻洪水风险和维持生态系统服务。我们的项目将调查每年季风洪水期间通过湄公河三角洲的水流和泥沙路线，并对相对海平面上升和通过分流河道和主要分流地点的泥沙路线过程对三角洲的影响有一个新的一般性理解。这将通过收集新的最先进的实地数据集、开发和应用形态动力学数值模型以及利用系统动力学模型来指导水产养殖和农业适应变化来实现。我们将利用我们必须参与的一系列现有联系，并将工作成果传达给该地区的机构和政策制定者，并在气候变化的背景下为水资源规划和缓解/适应战略提供信息。

The world's 33 largest deltas are being drowned by relative sea level rise and are, as a result, rapidly losing land. This process is also driving an exacerbation of flood risk in these environments, which is placing many large cities, key infrastructure and over 0.5 billion people at risk globally. These issues are most acute for deltas across Southern and Southeast Asia, where an estimated 20% of land will be lost by 2100. These risks are significant. For example, floods during the 2011 Asian monsoon killed an estimated 2000 people and caused ~US$45 billion in economic damage across SE Asia. Moreover, these deltas, and their ecosystem services, underpin regional food security for rapidly growing populations. There is therefore an urgent need to evolve an improved generic understanding of the processes behind the relative sea level rise and flood risk dynamics in these deltaic environments into the future. Significant recent advances have been made in our understanding of many aspects of delta morphodynamics and evolution. This has included work on distributary channel flow processes, bifurcation stability and bar dynamics, and the profound influence of tidal backwater effects on longer-term channel hydro- and sediment dynamics. However, despite this progress there are significant uncertainties around the influence of: i) upstream migrating backwater effects, forced by sea-level rise, on delta bifurcation stability; ii) declining sediment delivery and increased hydrological variability on distributary channel stability; iii) connectivity between the channels and the delta surface on the routing, dispersal and trapping of sediment. Each of these uncertainties are key knowledge gaps that must be addressed for effective delta management, flood risk mitigation and maintenance of ecosystem services. Our project will investigate flow and sediment routing through the Mekong delta across the annual monsoon flood and develop a new generic understanding of the impact of relative sea-level rise and sediment routing processes through distributary channels and key bifurcation sites on the delta. This will be achieved through collection of new state-of-the-art field datasets, development and application of morphodynamic numerical modelling and utilization of system dynamics modelling to guide aquaculture and agriculture adaptations to changes. We will leverage a range of existing links we have to engage with, and communicate the outcomes of the work, to agencies and policy makers in the region and inform water resource planning and mitigation/adaptation strategies in the context of climate change.