Ranasinghe Roshanka, Wang Zheng Bing, Bamunawala Janaka, Duong Trang Minh
Department of Coastal and Urban Risk & Resilience, IHE Delft Institute for Water Education, P.O. Box 3015, 2601 DA, Delft, The Netherlands.
Deltares, P.O. Box 177, 2600 MH, Delft, The Netherlands.
Sci Rep. 2025 Feb 4;15(1):4231. doi: 10.1038/s41598-025-86699-0.
Tidal inlets are a common feature along the world's coastline. Inlet-adjacent coastlines have for millennia supported communities and livelihoods, and therefore, projected climate change driven variations in catchment-estuary-coast (CEC) system drivers (e.g., sea-level rise (SLR)) are likely to lead to substantial socio-economic impacts. One important SLR-driven process that affects inlet-adjacent shoreline change is basin-infilling (i.e., sediment import to the estuary from the coast to satisfy the SLR-driven increase of estuarine accommodation space). Due to the slow morphological response to hydrodynamic forcing, however, there is a time lag between basin infilling and SLR, which, in numerical models that simulate century-scale evolution of CEC systems, is represented by a basin infilling lag factor (M). To date, an indicative M value has only been derived for small tidal inlet systems (M ~0.5), and due to the lack of M estimates for larger systems, studies have been using M ~0.5 indiscriminately. Here, for the first time, we derive indicative M values for small, medium, and large tidal inlet systems (M ~0.5, ~0.25 and ~0.15 respectively) via analytical considerations. Subsequently, to investigate the consequences of using sub-optimal M values on twenty-first century projections of inlet-adjacent shoreline change, we apply a probabilistic, reduced complexity model (G-SMIC), under four IPCC AR6 climate scenarios, to three CEC systems representing small, medium and large systems. Results show that, in general, shoreline change projections are substantially lower(higher) when M values smaller(larger) than the indicative M for a given system are used. When smaller-than-optimal M values (0.25 and 0.15) are used for the small tidal inlet, both mid- and end-century shoreline retreats are under-estimated by 50-75% (across the four climate scenarios), relative to projections obtained with the optimal M value. For the medium-sized inlet, shoreline retreats for both future periods are over-estimated by ~100% with the larger-than-optimal M value of 0.5, while they are under-estimated by ~40-75% (across climate scenarios) with the smaller-than-optimal M value of 0.15. When the two higher-than-optimal M values (0.25 and 0.5) are used for the large tidal inlet system, shoreline retreat is over-estimated by ~ 65-240% (across climate scenarios) for both future periods. In terms of absolute values, these under/over-estimations increase in time and with the severity of emission scenario.
潮汐汊道是世界海岸线的一个常见特征。数千年来，毗邻汊道的海岸线一直支撑着社区和生计，因此，预计气候变化驱动的集水区-河口-海岸（CEC）系统驱动因素（如海平面上升（SLR））的变化可能会导致重大的社会经济影响。影响毗邻汊道海岸线变化的一个重要的由海平面上升驱动的过程是盆地充填（即沉积物从海岸输入河口，以满足海平面上升驱动的河口容纳空间的增加）。然而，由于对水动力强迫的形态响应缓慢，盆地充填和海平面上升之间存在时间滞后，在模拟CEC系统百年尺度演化的数值模型中，这由盆地充填滞后因子（M）表示。迄今为止，仅针对小型潮汐汊道系统得出了一个指示性的M值（M约为0.5），由于缺乏大型系统的M估计值，研究一直不加区分地使用M约为0.5。在此，我们首次通过分析考虑得出了小型、中型和大型潮汐汊道系统的指示性M值（分别为M约为0.5、约为0.25和约为0.15）。随后，为了研究使用次优M值对21世纪毗邻汊道海岸线变化预测的影响，我们在四种IPCC AR6气候情景下，将一个概率性的、简化复杂性模型（G-SMIC）应用于代表小型、中型和大型系统的三个CEC系统。结果表明，一般来说，当使用小于（大于）给定系统指示性M值的M值时，海岸线变化预测值会显著降低（升高）。对于小型潮汐汊道，当使用小于最优值的M值（0.25和0.15）时，相对于使用最优M值获得的预测，本世纪中叶和末期的海岸线退缩估计值低了50-75%（在四种气候情景下）。对于中型汊道，使用大于最优值的M值0.5时，未来两个时期的海岸线退缩估计值高估了约100%，而使用小于最优值的M值0.15时，低估了约40-75%（在各种气候情景下）。对于大型潮汐汊道系统，当使用两个大于最优值的M值（0.25和0.5）时，未来两个时期的海岸线退缩估计值高估了约65-240%（在各种气候情景下）。就绝对值而言，这些低估/高估会随着时间和排放情景的严重性而增加。
