Tidally Driven Interannual Variation in Extreme Sea Level Frequencies in the Gulf of Maine
Tidally Driven Interannual Variation in Extreme Sea Level Frequencies in the Gulf of Maine
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DOI：
10.1029/2020jc016291
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发表时间：
2020-10-01
影响因子：
3.6
通讯作者：
DeConto, R. M.
中科院分区：
文献类型：
--
作者：
Baranes, H. E.;Woodruff, J. D.;DeConto, R. M.
潮汐强度的天文变化可以强烈地调节沿海洪水在日、月和年际时间尺度上的严重程度。在这里，我们提出了一个新的准非平稳斜浪涌联合概率方法（qn-SSJPM），估计洪水灾害造成的18.6年和准4.4年调制的潮汐年际波动。我们证明，qn-SSJPM派生风暴潮频率估计更精确和稳定的标准实践相比，拟合的极值分布测量风暴潮，这往往是由最大的几个事件在观测期间的偏差。应用qn-SSJPM在缅因州湾，我们发现显着的潮汐强迫冬季风暴季节洪水灾害的18.6年的节点周期，而4.4年的调制和长期趋势的潮汐是小的年际变化和长期趋势的海平面。在1%的年机会风暴潮中，波节周期迫使十年振荡，在Eastport，ME的平均速率为13.5 mm/年;在波特兰，ME的平均速率为4.0 mm/年;在波士顿，MA的平均速率为5.9 mm/年。目前（2020年），节点强迫正在抵消海平面上升引起的洪水危险增加;然而，到2025年，节点周期将达到最小值，然后在接下来的十年中随着洪水走向最大阶段，开始加速洪水危险增加。沿着世界的中到大潮汐海岸线，因此，在规划过渡到慢性洪水，将在未来世纪海平面上升驱动的潮汐非平稳性是至关重要的。简单的语言摘要围绕洪水风险的沿海管理实践往往依赖于一年内发生特定洪水高度的概率百分比的估计。例如，美国的洪水保险要求指定具有100年一遇洪水重现期的地区（“百年洪水区”）。当风暴袭击有大潮汐的地区时，高潮的高度和时间往往决定洪水的严重程度。因此，洪水高度和年频率之间的关系可以通过潮汐高度的自然、每日至十年周期性变化来改变。在这里，我们提出了一种新的方法来计算每年变化的洪水高度频率关系的基础上已知的潮汐周期。应用新方法在缅因州的海湾，我们发现一个18.6年的潮汐周期（节点周期）迫使1%的年机会洪水的年代际变化的速度比历史平均海平面上升率在过去的世纪。目前，节点周期强迫正在抵消海平面上升引起的洪水灾害的增加;然而，在2025年，节点周期将达到最低限度的海湾，然后开始加速洪水灾害，因为它在随后的十年中走向其最大值。因此，在中期洪水灾害规划中考虑海平面上升和潮汐变化是至关重要的。关键点我们提出了一种新的准非平稳联合概率方法，估计潮汐驱动的洪水灾害年际波动。这种方法提供了比极端值分布更精确和稳定的风暴潮频率估计，以适应测量的风暴潮在缅因州湾，潮汐以超过历史平均海平面上升的速度，迫使1%的年机会风暴潮发生年代际振荡
Astronomical variations in tidal magnitude can strongly modulate the severity of coastal flooding on daily, monthly, and interannual timescales. Here we present a new quasi-nonstationary skew surge joint probability method (qn-SSJPM) that estimates interannual fluctuations in flood hazard caused by the 18.6- and quasi 4.4-year modulations of tides. We demonstrate that qn-SSJPM-derived storm tide frequency estimates are more precise and stable compared with the standard practice of fitting an extreme value distribution to measured storm tides, which is often biased by the largest few events within the observational period. Applying the qn-SSJPM in the Gulf of Maine, we find significant tidal forcing of winter storm season flood hazard by the 18.6-year nodal cycle, whereas 4.4-year modulations and a secular trend in tides are small compared to interannual variation and long-term trends in sea-level. The nodal cycle forces decadal oscillations in the 1% annual chance storm tide at an average rate of 13.5 mm/year in Eastport, ME; 4.0 mm/year in Portland, ME; and 5.9 mm/year in Boston, MA. Currently (in 2020), nodal forcing is counteracting the sea-level rise-induced increase in flood hazard; however, in 2025, the nodal cycle will reach a minimum and then begin to accelerate flood hazard increase as it moves toward its maximum phase over the subsequent decade. Along the world's meso-to-macrotidal coastlines, it is therefore critical to consider both sea-level rise and tidal nonstationarity in planning for the transition to chronic flooding that will be driven by sea-level rise in many regions over the next century.Plain Language Summary Coastal management practices around flood risk often rely on estimates of the percent chance of a particular flood height occurring within a year. For example, U.S. flood insurance requires designating areas with a 100-year flood recurrence interval (the "100-year flood zone"). When storms hit regions with large tides, the height and timing of high tide often determine flood severity. Thus, the relationship between flood height and annual frequency can be altered by natural, daily-to-decadal cyclical variation in tide heights. Here we present a new method for calculating annually varying flood height-frequency relationships based on known tidal cycles. Applying the new method in the Gulf of Maine, we find an 18.6-year-long tidal cycle (the nodal cycle) has forced decadal variation in the 1% annual chance flood at a faster rate than the historical average rate of sea-level rise over the past century. Currently, nodal cycle forcing is counteracting the sea-level rise-induced increase in flood hazard; however, in 2025, the nodal cycle will reach a minimum in the Gulf and then begin to accelerate flood hazard as it moves toward its maximum over the subsequent decade. It is therefore critical to consider sea-level rise and tidal variation in medium-term flood hazard planning.Key PointsWe present a new quasi-nonstationary joint probability method that estimates tidally driven interannual fluctuations in flood hazard This method provides more precise and stable storm tide frequency estimates than extreme value distributions fit to measured storm tides In the Gulf of Maine, tides force decadal oscillations in the 1% annual chance storm tide at a rate exceeding mean historical sea-level rise