Moskvichev Richelle U, Mikkelsen Anna B, Anderson Tiffany R, Vitousek Sean F, Nicolow Joel C, Fletcher Charles H
Department of Earth Sciences, School of Ocean and Earth Science and Technology, University of Hawai'i at Mānoa, Honolulu, HI, 96822, USA.
United States Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA, 95060, USA.
Sci Rep. 2025 Mar 28;15(1):10794. doi: 10.1038/s41598-025-95074-y.
Coastal erosion, intensified by sea level rise, poses significant threats to coastal communities in Hawai'i and similar island communities. This study projects long-term shoreline change on the Hawaiian Island of O'ahu using the data-assimilated CoSMoS-COAST shoreline change model. CoSMoS-COAST models four key shoreline processes: (1) Alongshore transport, (2) Recession due to sea level rise, (3) Cross-shore transport due to waves, and (4) Residual processes represented by a linear trend term. This study marks the first application of CoSMoS-COAST for an oceanic equatorial island with narrow beaches and a dynamic wave climate. The model is informed with a novel combination of shoreline data derived from high-resolution imagery from Planet, Sentinel-2, and Landsat satellites, wave-climate hindcasts specific to Hawai'i, and regional beach-slope surveys. On a dynamic northern O'ahu beach, the model achieved a root mean square error of 9.4 m between observations and model output. CoSMoS-COAST predicts that 81% of O'ahu's sandy beach coastline could experience beach loss by 2100; with 39.8% of this loss happening by 2030. This represents an increase, 43.3%, in net landward shoreline change compared to previous erosion forecasts, for 0.3 m of sea level rise (2050). Additionally, dynamic processes such as cross-shore equilibrium processes and alongshore sediment transport, play a large contribution to gross shoreline change within the next decade, particularly on O 'ahu's north and west shores. In the long term, we find that recession due to sea level rise and residual processes dominate, but dynamic, wave-driven processes (longshore and cross-shore transport) still account for 34% of shoreline change between present and 2100. We assert dynamic, wave-driven processes are a crucial addition for accurate modeling of island sandy beach environments. These findings have implications for O'ahu's coastal planning and development, suggesting updates to shoreline policies that rely upon erosion forecasting, and highlights the importance of incorporating wave and alongshore transport in erosion models for other Pacific islands.
海平面上升加剧了海岸侵蚀，对夏威夷的沿海社区以及类似的岛屿社区构成了重大威胁。本研究使用数据同化的CoSMoS-COAST海岸线变化模型预测了瓦胡岛的长期海岸线变化。CoSMoS-COAST对四个关键的海岸线过程进行建模：（1）沿岸输运；（2）海平面上升导致的海岸线后退；（3）波浪引起的跨岸输运；（4）由线性趋势项表示的残余过程。本研究标志着CoSMoS-COAST首次应用于具有狭窄海滩和动态波浪气候的赤道海洋岛屿。该模型采用了来自Planet、哨兵2号和陆地卫星的高分辨率图像得出的海岸线数据、夏威夷特定的波浪气候后报以及区域海滩坡度调查的新颖组合。在瓦胡岛北部一个动态海滩上，该模型在观测值与模型输出之间的均方根误差为9.4米。CoSMoS-COAST预测，到2100年，瓦胡岛81%的沙滩海岸线可能会出现海滩侵蚀；其中39.8%的侵蚀将在2030年发生。这意味着与之前海平面上升0.3米（2050年）时的侵蚀预测相比，净向陆海岸线变化增加了43.3%。此外，诸如跨岸平衡过程和沿岸泥沙输运等动态过程，对未来十年内的总海岸线变化贡献很大，尤其是在瓦胡岛的北岸和西岸。从长期来看，我们发现海平面上升导致的后退和残余过程占主导，但动态的、由波浪驱动的过程（沿岸和跨岸输运）在当前至2100年期间仍占海岸线变化的34%。我们断言，动态的、由波浪驱动的过程是精确模拟岛屿沙滩环境的关键补充。这些发现对瓦胡岛的海岸规划和发展具有启示意义，建议更新依赖侵蚀预测的海岸线政策，并突出了在其他太平洋岛屿的侵蚀模型中纳入波浪和沿岸输运的重要性。
