Canute

This project, undertaken with staff at the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), was aimed at providing estimates of current extreme sea level (exclusive of surface gravity waves) exceedence probabilities around the whole coastline of Australia, arising from combinations of mean sea level, astronomical tide and storm surges generated by both extra-topical and tropical storms. In the first stage of the study, a high resolution (2.5 km along the coast) hydrodynamic depth averaged tide-surge model has been configured for the whole coastline of Australia using the Danish Hydraulics Institute’s Mike21 modelling suite of tools. The model has been forced with astronomical tidal levels, derived from the TPX07.2 global tidal model, and meteorological fields, from the US National Center for Environmental Prediction’s global reanalysis, to generate a 40-year (1970 to 2009) hindcast of water levels. This modelled dataset has been validated against measurements from 29 tide gauge sites around Australia with long records. At each of the model grid points located around the coast, time series of annual maxima and the several largest water levels each year were derived from the multi-decadal sea level hindcast and have been fitted to extreme value distributions to estimate exceedence probabilities. This provides a reliable estimate of current sea level exceedence probabilities around southern Australia, which is mainly impacted by extra- tropical storms. However, as the meteorological forcing used only weakly includes the effects of tropical cyclones the resultant extreme sea level probabilities are underestimated around western and northern Australia. The second stage of the study is underway to more accurately include tropical cyclone-induced surges in the estimation of extreme sea level probabilities around western and northern Australia.