Large parts of the world's coastlines are exposed to extreme high-water levels, which have the potential to cause widespread flooding and costly damages (Nicholls et al., 2007; Haigh et al., 2011; Pugh and Woodworth, 2014). Knowledge on potential water level extremes is thus essential for coastal protection strategies and is usually building upon observations (e.g., from tide gauges). These instruments measure the local water level in response to astronomical (i.e., tide) and meteorological forcing (i.e., surge) superimposed onto the base water level (i.e., mean sea level). For more than 60 years, nonlinear tide-surge interactions (TSI) have been reported for many places but no global quantification was available so far. Here, a novel approach to statistically assess TSI is presented (see also Arns et al., 2020). The approach is useful to value TSI contributions to total water levels by up to 30% or 70 cm at some places, a value which is similiar to recent sea level rise projections by 2100 (based on a temperature increase of +1.5° by 2100). Conversely, extreme value analysis — as routinely utilized by current coastal impact studies — may overestimate return water levels by an amount equal to or larger than future sea level rise projections, if TSI is not accounted for. Not accounting for TSI also leads to an overestimation of present-day coastal exposure. Using the DIVA modeling framework, reduced estimates of global sea-flood costs by nearly 16% and population exposed by almost 8% are found when TSI is considered.

In March 2020, Arne Arns became Professor for Coastal Protection and Coastal Dynamics at the University of Rostock. Since the beginning of his Ph.D. at the University of Siegen in 2009, Arne has investigated the risk of storm surges and coastal floods around the world. His work focuses in particular on climate-induced influences on coastal extremes, as well as on underlying interactions.

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