Trends in Europe storm surge extremes match the rate of sea-level rise

Abstract

Coastal communities across the world are already feeling the disastrous impacts of climate change through changes in extreme sea levels 1 . These changes reflect the combined effect of sea-level rise and changes in storm surge activity. Understanding the relative importance of these two factors in altering the likelihood of extreme events is crucial to the success of coastal adaptation measures. Existing analyses of tide gauge records 2-10 agree that sea-level rise has been a major driver of trends in sea-level extremes since at least 1960. However, the contribution from changes in storminess remains unclear, owing to the difficulty of inferring this contribution from sparse data and the consequent inconclusive results that have accumulated in the literature 11,12 . Here, we analyse tide gauge observations using spatial Bayesian methods 13 to show that, contrary to current thought, trends in surge extremes in Europe since 1960 were comparable to the rate of sea-level rise. We determine that the trend pattern of surge extremes reflects the contributions from a dominant north-south dipole associated with internal climate variability and a single-sign positive pattern related to anthropogenic forcing. Our results demonstrate that both external and internal influences can considerably affect the likelihood of surge extremes over periods as long as 60 years, suggesting that the current coastal planning practice of assuming stationary surge extremes 1,14 might be inadequate.Floods resulting from extreme sea levels are among the costliest natural hazards, causing tens of billions of dollars in economic losses globally each year 1 . Without adaption, such losses are certain to worsen in the decades ahead as sea level rises 15,16 . Cost-effective adaptation plans are key to reducing this vulnerability while also avoiding costly overprotection measures 17 . However, their success relies on robust understanding of how changes in mean climate affect the likelihood of extreme sea-level events. This effect can occur primarily through (omitting tides and waves) changes in storminess affecting the occurrences of storm surges, and changes in mean sea level (MSL) raising or lowering the baseline level for storm surges. While most studies agree that sea-level rise 18,19 has made extreme sea-level events more likely across the world since at least the mid-20 th century 2-10 , the contribution from changes in surge extremes is subject to debate 11,12 .Clarifying this debate is a priority because, in most countries, current practice for assessing future coastal flood risk assumes that the probability of surge extremes is the same now as in the future 1,14 (i.e., only sea-level rise is considered). Should this assumption turn out to be invalid, this could cause adaptation plans to be ineffective.Numerical models generally predict that storm surge activity will change this century in many places as the climate warms [20][21][22][23][24][25][26] , albeit with varying intensity depending on the study. Yet observational evidence for such c...

Advances in the observation and understanding of changes in sea level and tides

“…This finding has since been largely confirmed by other authors using tide gauge records from particular locations or in different regions (e.g., Ref. 155). Menéndez and Woodworth also demonstrated the dependence of extremes on MSL on interannual timescales (e.g., due to the El Niño‐Southern Oscillation ENSO), as well as on long‐term MSL change.…”

Shift of the storm surge season in Europe due to climate variability

“…at New York 18 . At first order, changes in storm surges are relative to changes in mean sea level 1 , 19 . After removing the mean sea level contribution, storm surges display strong interannual to multidecadal variability, and this variability is mainly controlled by the large-scale atmospheric forcing.…”

Planning for Climate Change Impacts on Geoheritage Interests in Protected and Conserved Areas

“…For example, by 2100, under the intermediate greenhouse gas emissions scenario, global mean sea level is likely to rise by 0.44-0.76 m relative to 1995-2014, but could approach 2 m under a very high emissions scenario (IPCC 2021). However, rates will vary geographically according to gravitational effects, ocean circulation factors and variations in vertical land movements arising from glacio-isostatic adjustments and tectonic factors, with effects exacerbated regionally by increased frequency of extreme sea levels arising from a combination of storm surges, waves and tides (Tebaldi et al 2021;Calafat et al 2022). Use of regional rather than global estimates is therefore recommended for management planning of responses in PCAs in order to reduce the uncertainty in scale and timing of effects in local areas.…”