Abstract
Studies of changes in wave climate typically consider trends in sea state statistics, such as the significant wave height. However, the temporal variability of individual rogue waves, which pose a hazard to users of the sea and coastal environment has not been investigated. We use time series of continuous surface elevation over 124–270 months (spanning 1994–2016), from 15 wave buoys along the US western seaboard, to investigate regional trends in significant wave height and individual rogue waves. We find high spatial variability in trends in significant wave height and rogue waves across the region. Rogue wave occurrence displays a mostly decreasing trend, but the relative height – or severity – of the waves is increasing. We also identify seasonal intensification in rogue waves with increased rogue wave occurrence, of higher severity, in the winter than in the summer. Therefore, the common practice of stating a single occurrence likelihood for an ocean basin is not valid. In addition, the buoy data show that the magnitude and significance of trends in significant wave height increases towards higher percentiles, supporting previous findings.
Highlights
IntroductionYoung et al.[3], analysed satellite altimetry from 1985–2008 that indicated weak trends in monthly global mean significant wave height (HS) and indicated that the largest waves (90th and 99th percentile Hs) have increased in amplitude over this period
Global mean significant wave height has increased over the past 30 years[1,2,3]
Are Wave Heights Increasing? The mean Hs over the sampling period of the buoys show small decreasing trends of less than 0.5% yr−1 for most buoys; these are not statistically significant (Red bars – Fig. 2) they are similar to what is seen in satellite data[3]
Summary
Young et al.[3], analysed satellite altimetry from 1985–2008 that indicated weak trends in monthly global mean significant wave height (HS) and indicated that the largest waves (90th and 99th percentile Hs) have increased in amplitude over this period. This is true for waves along the highly populous western seaboard of the United States of America. These were shown to be increasing, with 90th and 99th percentile of mean monthly Hs increasing by over 1% per year, over a 23 year period[3].
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