Changes in the Seasonal Cycle of Storm Surge and Mean Sea Level Along the Global Coastline

Storm surge events are a key driver of widespread flooding, particularly when combined with astronomical tides superimposed on mean sea level (MSL). Coastal storms exhibit seasonal variability which translates into a seasonal cycle in storm surge activity. It has been demonstrated before that the seasonal cycle shows significant interannual variations including possible long-term trends. Understanding these changes is critical as both changes in the amplitude and the phase of their seasonal cycle may alter the compound flood potential. Changes in the seasonal storm surge cycle and the compounding with the MSL cycle remain largely unknown. A comprehensive analysis of the storm surge seasonal cycle and its links to the MSL seasonal cycle is performed using tide gauge observations from a quasi-global dataset. Harmonic analysis is used to assess the mean and changing storm surge seasonal cycles over time. Extreme value analysis is applied to explore the effect of seasonal changes on storm surge return levels. We also quantify the influence of large-scale climate modes, and we compare how the seasonalities of storm surge and MSL have changed relative to each other. The peak of the storm surge cycle typically occurs during winter for tide gauges outside of tropical cyclone regions, where there is greater variability in the phase of the storm surge cycle. The timing of the peak varied by more than a month at 21% of the tide gauges analyzed. The MSL and storm surge cycles peaked at least once within 30 days at 74% of tide gauges.