Is the 100-Year Return Value for Significant Wave Height Increasing in the Tasman Sea?

Abstract

Abstract Climate change is frequently reported to be the cause of an apparent increase in the occurrence and intensity of extreme events around the globe. Recent studies have found that increases can be expected in sea state extremes for some regions of the world’s oceans. We investigate temporal trends in storm peak significant wave height for a central Tasman Sea location, using output from the FIO-ESM v2.0 CMIP6 Earth System Model of [1], [2]. These data include time-series of significant wave height for several Shared Socioeconomic Pathways (SSP) as well as 165-year historical and 700-year pre-industrial realisations. This allows estimates to be made of 100-year return values for significant wave height at the end of the 21st century, for several future atmospheric forcing scenarios, and comparison of these against estimates for present day, based on the historical data base, and estimates for pre-industrial conditions. The estimates are made with a non-stationary extreme value analysis method that allows return values of storm peak significant wave height to be estimated as a function of time and to quantify if changes in return values are statistically significant. Evidence supporting climate-related changes at the Tasman location studied is weak. Estimates of most probable changes in 100-year return value for storm peak significant wave height between 2015 and 2100, for the three SSP scenarios considered, suggest the assumption of a 2m increase in 100-year return value to be reasonable, whilst noting that this value is small compared to the inherent uncertainty (of at least ±5m) present.