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- Title
Quantifying the Mean Sea Level, Tide, and Surge Contributions to Changing Coastal High Water Levels.
- Authors
Palmer, Karen; Watson, Christopher S.; Power, Hannah E.; Hunter, John R.
- Abstract
The likelihood of coastal inundation (high tide flooding) depends on the coincidence of mean sea level (MSL), high tide, and surge, relative to the height of local thresholds. Here we present a nonparametric Joint Probability of Maxima Method for deriving frequency‐based exceedance thresholds and for quantifying the changing heights of water level maxima. Our approach builds upon the Skew Surge Joint Probability Method (Batstone et al., 2013, https://doi.org/10.1016/j.oceaneng.2013.02.003) in using predicted high water (HW) level and skew surge components, adding MSL as a third component, and accounting for seasonal variation. From the derived distributions, we obtain threshold levels exceeded at specific average recurrence intervals of 1, 5, and 10 years. Changes in exceedances are compared between two 19‐year epochs for 166 tide gauges: 140 from a global data set (GESLA: 1983–2001 vs. 2002–2020), and 26 from an Australian data set (BoM: 1992–2010 vs. 2004–2022). We find that the change in exceedance levels between epochs typically exceeds the respective change in MSL and varies between the different threshold levels. We quantify the specific contribution of each component, finding that MSL contributions are influential at most sites, while tides contribute a lesser amount, and surge contributions vary substantially. Exceedance frequency more than doubles on average and increases most at those locations with the smallest variability in the height of high tide. Our approach serves to address a critical gap in offering specific and localized measures of changes in coastal inundation frequency. Plain Language Summary: Any change in the height or timing of mean sea level (MSL), tides, or surges results in a change in the probability of coastal flooding. We developed a way to represent every likely combination of MSL, high tide, and surge for two 19‐year periods, a timespan that is long enough to account for natural differences in tides and seasons associated with surges. Our method combines only the tides and surges that occur during the same season, improving on previous similar approaches. We used observations from 166 tide gauges, comparing changes between periods from 1983–2001 to 2002–2020 for a global data set (GESLA), and between overlapping periods from 1992–2010 to 2004–2022 for an Australian data set (BoM). The comparison between these periods allowed us to calculate the height that a coastal barrier would need to be modified to avoid more frequent flooding, and to quantify the individual amounts from changes in MSL, tides, and surges. Higher MSL was commonly associated with higher flood probability, but changes in tides and surges made important differences for many sites. On average, a coastal barrier exceeded once per year in the earlier period was overtopped at least twice per year in the more recent period. Key Points: A new joint probability method enables determination of individual contributions to the changing likelihood of coastal floodingIndividual additions/subtractions made by mean sea level (MSL), tide, and surge components vary by return period, by region, and site to siteOn average, the sum of contributions to changed high water levels between the periods compared was greater than from MSL alone
- Subjects
SEA level; COASTAL changes; WATER levels; TERRITORIAL waters; FLOODS; STORM surges
- Publication
Journal of Geophysical Research. Oceans, 2024, Vol 129, Issue 8, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2023JC020737