Sea-level rise around the Australian coastline and the changing frequency of extreme events

Sea-level rise is one of the well-known impacts of climate change. Arecently completed analysis of available tide-gauge data for the period 1950 to 2000 indicates a global average rate of sea-level rise of 1.8 ± 0.3 mm per year. For this period, the analysis indicates a minimum sea-level rise to the northwest of Australia. Here, we find that the change of relative mean sea level around the Australian coastline for the period 1920 to 2000 is about 1.2 mm per year. There are only two records sufficiently long to examine changes in the frequency of extreme events, Fremantle and Fort Denison, Sydney. For both locations, there is a decrease in the average recurrence interval (ARI) by factors of about three for extreme sea levels from the pre-1950 period to the post-1950 period. We also demonstrate a method for estimating the frequency of extreme events from a combination of tides and storm surges for locations with little or no data. For Cairns, we find that the 1-in-100 year sea-level event increases in height from about 2.5 m to 2.9 m by 2050 as a result of a modest future sea-level rise and possible future changes in cyclone intensity. Equivalently, the ARI period of a 2.5 m event would decrease from 100 years to about 40 years.