The impact of future changes in weather patterns on extreme sea levels over southern Australia

This study first compares two methods by which the global, variable resolution Cubic Conformal Atmospheric Model (CCAM) is forced by reanalysis over Australia. The methods are the spectral nudging and bias-corrected sea surface temperature (SST) forcing. Surface winds and sea level pressure are compared since these influence coastal sea levels. SST forcing was found to better preserve the mean and standard deviation of these quantities. Second, a hydrodynamic model is used to model sea levels over southern Australia over 1980\textendash1999 and 2080\textendash2099 to investigate how changes in weather patterns affect extreme sea levels. Forcing from one Global Climate Model (GCM) and two CCAM simulations in which CCAM was used to downscale two GCMs over Australia with bias-corrected SST forcing (including the GCM considered in this study) were used. While there are differences in the spatial patterns of change between seasons over the modeled coastline between the three models, extreme sea levels were mostly lower in the future period over the southern mainland coastline from autumn to spring due to reduced westerlies in the climate models. The sea level changes around Tasmania varied from positive to negative depending on the model and season. The projected extreme sea level changes were within 10 cm of current climate values. This suggests that over southern Australia extreme sea level changes will be dominated by changes in mean sea level due to thermal expansion and ice sheet and glacier melt rather than changes in weather patterns.