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Predicting beach rotation using multiple atmospheric indices
Marine Geology ( IF 2.9 ) Pub Date : 2020-05-05 , DOI: 10.1016/j.margeo.2020.106207
Mark Wiggins , Tim Scott , Gerd Masselink , R. Jak McCarroll , Paul Russell

Shoreline change in the form of beach rotation can occur at event to decadal timescales, especially in semi-sheltered embayments with bi-directional wave climates, leading to enhanced coastal vulnerability under predictions of increased sea level rise. Previous studies have shown that phases of winter-averaged atmospheric indices in the North Atlantic correlate with variations in average winter wave height and dominant direction; however, predictions of a localised wave climate and beach rotation from individual climate indices has exhibited limited skill. Here we show that the combination of two major north Atlantic climate indices, the North Atlantic Oscillation (NAO) and West Europe Pressure Anomaly (WEPA), improves the prediction of a wave power directionality index (WDI), known to correlate with beach rotation along the length of a headland bound gravel embayment. Results using a combination of NAO and WEPA, improves predictions of WDI with an associated R2 of 0.66, when compared to 0.23 and 0.31 for NAO and WEPA individually. Hindcast (WDIWW3) and index predicted (WDIPred) values of the WDI were shown to validate against measured beach rotation from 2008 to 2018 and modelled inshore potential longshore energy fluxes from 1980 to 2018. A long-term historic time series of WDIPred (1906–present) was then hindcast using records of NAO and WEPA. Qualitative validation of long-term beach rotation in response to the WDIPred is achieved with proxy records of beach change in the form of oblique and aerial photography and topographic maps. Low frequency (~60 years) beach rotation is shown to follow phases of the detrended cumulative WDIPred values, over the period of 1906 to 2018, linked to the multi-decadal fluctuations in detrended cumulative values of NAO and WEPA. When examined in the context of millennial-scale proxy NAO records, it is clear the recent centurial-scale analysis does not capture past variability and duration. This work has shown that: (1) potential future season ahead forecasts of atmospheric indices may skilfully predict beach rotation in many regions with bi-directional wave climates; and (2) historical analysis highlights the potential past phases of extreme coastal realignment. These new insights will lead to proactive and informed management from local authorities and coastal engineers.



中文翻译:

使用多个大气指数预测海滩旋转

沿海滩旋转形式的海岸线变化可能会在年代际尺度上发生,尤其是在双向波浪气候的半遮蔽式掩体中,在海平面上升趋势增加的预测下,沿海脆弱性将增强。先前的研究表明,北大西洋冬季平均大气指数的相位与冬季平均波高和主导方向的变化有关。然而,根据个别气候指数对局部海浪气候和海滩旋转的预测显示出有限的技能。在这里,我们表明,北大西洋涛动(NAO)和西欧压力异常(WEPA)这两个主要的北大西洋气候指数相结合,可以改善对波功率方向性指数(WDI)的预测,已知与沿岬角限制的砾石嵌入长度的海滩旋转相关。将NAO和WEPA结合使用的结果可改善WDI与相关R的预测2个为0.66,而NAO和WEPA分别为0.23和0.31。显示了WDI的Hindcast(WDI WW3 和指数预测(WDI Pred)值,可以验证从2008年至2018年的测量海滩旋转并模拟1980年至2018年的近岸潜在近岸能量通量。WDI Pred的长期历史时间序列然后使用NAO和WEPA的记录进行后播(1906年至今)。WDI Pred对海滩长期旋转的定性验证是通过倾斜,航空摄影和地形图形式的海滩变化的代理记录来实现的。低频(〜60年)海滩旋转被证明遵循下降趋势的累积WDI Pred阶段1906年至2018年期间的数值与NAO和WEPA下降趋势累积值的数十年波动有关。在千禧世代代理NAO记录的背景下进行检查时,很明显,最近的百年尺度分析没有捕获过去的可变性和持续时间。这项工作表明:(1)在未来可能出现的季节预报中,大气指数可能巧妙地预测了双向波气候下许多地区的海滩旋转;(2)历史分析突出了极端沿海调整的潜在过去阶段。这些新见解将导致地方当局和沿海工程师的主动和知情管理。

更新日期:2020-05-05
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