Should Swedish sea level planners worry more about mean sea level rise or sea level extremes?

Abstract

Current coastal spatial planning in Sweden uses simple methods to account for how flood risks increase owing to sea level rise. Those methods, however, fail to account for several important aspects of sea level rise, such as: projection uncertainty, emission scenario uncertainty and time dependence. Here, enhanced methods that account for these uncertainties are applied at several locations along the coast. The relative importance of mean sea level rise and extreme events for flood risk is explored for different timeframes. A general conclusion for all locations is that, extreme events dominate the flood risk for planning periods lasting a few decades. For longer planning periods, lasting toward the end of the century, the flood risk is instead dominated by the risk of high sea level rise. It is argued that these findings are important for assessments of future flood risk, and that they should be reflected in coastal spatial planning.

The sea level simulator v1.0: a model for integration of mean sea level change and sea level extremes into a joint probabilistic framework

“…problem, the time dependence of mean sea level change is rarely accurately accounted for in current coastal spatial planning (Hieronymus, 2021;Hieronymus and Kalén, 2022). Neither is, generally speaking, the uncertainty encompassed in probabilistic mean sea level projections.…”

“…The sea level simulator framework introduced by Hieronymus (2021) and further developed by Hieronymus and Kalén (2022) rids the planner of much of the ambiguity inherent in these arbitrary levels. This is done by calculating flood risk as a function of height above the current mean sea level.…”

“…Such as: implementation of new mean sea level scenarios, better uncertainty quantifications for sea level extremes and a more realistic time dependence in the mean sea level projections. All of these improvements were absent in the simulator used by Hieronymus (2021) and Hieronymus and Kalén (2022). Moreover, the current paper is also intended to be the main technical reference for the first public release of the sea level simulator.…”

“…caused by both mean sea level rise and sea level extremes) experienced within the planning period, information is also stored about the heights of the mean sea level and the sea level extreme components individually. The latter information is important to gauge potential impacts and to produce more informed risk assessments as was discussed by Hieronymus and Kalén (2022).…”

“…This is done using the gevfit routine from Matlab's statistics toolbox. In earlier versions of the simulator (Hieronymus, 2021;Hieronymus and Kalén, 2022), only the maximum likelihood estimate of the GEV parameters was used to characterize the tide gauge. That is, in earlier versions there were no uncertainty in which GEV distribution the simulator used.…”