Understanding extreme sea levels for broad-scale coastal impact and adaptation analysis

T Wahl,A Arns,J Hinkel,R J Nicholls,I D Haigh,A B A Slangen,S Dangendorf

doi:10.1038/ncomms16075

Abstract

One of the main consequences of mean sea level rise (SLR) on human settlements is an increase in flood risk due to an increase in the intensity and frequency of extreme sea levels (ESL). While substantial research efforts are directed towards quantifying projections and uncertainties of future global and regional SLR, corresponding uncertainties in contemporary ESL have not been assessed and projections are limited. Here we quantify, for the first time at global scale, the uncertainties in present-day ESL estimates, which have by default been ignored in broad-scale sea-level rise impact assessments to date. ESL uncertainties exceed those from global SLR projections and, assuming that we meet the Paris agreement goals, the projected SLR itself by the end of the century in many regions. Both uncertainties in SLR projections and ESL estimates need to be understood and combined to fully assess potential impacts and adaptation needs.

Highlights

One of the main consequences of mean sea level rise (SLR) on human settlements is an increase in flood risk due to an increase in the intensity and frequency of extreme sea levels (ESL)
We find that uncertainties in contemporary ESL estimates are at least as important as uncertainties in SLR projections, with the latter becoming more dominant when focusing on time periods farther in the future
In broad-scale impact assessments, ESL are typically represented by a set of parametric distributions that are commonly used by engineers to design infrastructure or to define flood zones[11,12]

Summary

Introduction

One of the main consequences of mean sea level rise (SLR) on human settlements is an increase in flood risk due to an increase in the intensity and frequency of extreme sea levels (ESL). We analyse changes in the return period by 2050 due to changing sea level[21,22] under the Representative Concentration Pathway (RCP) 4.5 of what is currently being assumed a 100-year event; we compare results from GPD99, identified here as a good global approach to parameterize ESL, and the GUM-AMAX method used in previous global assessments[3,14,15,16] (Fig. 4a,b).

Results

Conclusion