The timing of decreasing coastal flood protection due to sea-level rise

Sea-level rise poses a considerable threat to many coastal areas as it increases the exceedance probability of local protection infrastructure. Here, the authors propose a method that shows the different timing at which the degree of local protection decreases due to sea-level rise. Sea-level rise amplifies the frequency of extreme sea levels by raising their baseline height. Amplifications are often projected for arbitrary future years and benchmark frequencies. Consequently, such projections do not indicate when flood risk thresholds may be crossed given the current degree of local coastal protection. To better support adaptation planning and comparative vulnerability analyses, we project the timing of the frequency amplification of extreme sea levels relative to estimated local flood protection standards, using sea-level rise projections of IPCC AR6 until 2150. Our central estimates indicate that those degrees of protection will be exceeded ten times as frequently within the next 30 years (the lead time that large adaptation measures may take) at 26% and 32% of the tide gauges considered, and annually at 4% and 8%, for a low- and high-emissions scenario, respectively. Adaptation planners may use our framework to assess the available lead time and useful lifetime of protective infrastructure.

Automated summary

Sea-level rise increases the likelihood of exceeding local protection infrastructure, and the authors propose a method to determine when the degree of local protection decreases. This study projects the timing of extreme sea level frequency amplification relative to estimated local flood protection standards. Results show that within the next 30 years, the frequency of exceeding protection standards will significantly increase at a high proportion of tide gauges under different emissions scenarios.