A climatology of tropical cyclone (TC) impacts has been prepared. The climatology reveals that all coastal regions of Australia, from the southwest corner of Western Australia across the northern coastline and down the east coast as far as Sydney are potentially exposed to tropical cyclone impacts on an annual basis. The most affected area in terms of frequency of impacts is the tropical coastline, but the most vulnerable region is the tropical east coast which has a much higher and a rapidly increasing population, compared with the sparsely settled tropical west and north coasts.

The Australian Tropical Cyclone Database (ATCDB) has been used to compile statistics of Australian TC frequency, intensity, duration and track location as a reference for an enhanced greenhouse gas climate simulation generated by a variable resolution atmosphere-ocean Coupled General Circulation Model (CGCM), currently run at the University of Oklahoma, and referred to as the HIRES CGCM. The atmospheric model is run at approximately 1.8 degrees horizontal resolution globally, with a locally enhanced resolution of 0.5 degrees over the area of interest. A 100-year integration was carried out from 1970 to 2070, with monotonically increasing CO2 levels commencing after 2000, such that CO2 doubling is reached at 2070. There is a spin-up period of 20 years from 1950 to 1970. The general performance of the model is evaluated over the period 1970 to 2000, by comparing the TC-like vortices generated by the HIRES CGCM directly with the TCs archived in the ATCDB. The period 2000 to 2070 is then used to quantify the same TC characteristics, and to detect any trends discernible after 2000.

There are a number of findings that are of interest: there is a small but steady increase in the frequency of TCs over the Australian region; there is also a small but steady increase in the number of landfalling TCs; the TC season is extended by over 2 weeks; there is a spread of TC genesis and propagation further polewards by almost 2 degrees of latitude, with consequent serious implications for the heavily populated regions of coastal southeast Queensland and central and northern New South Wales. Finally, Ocean SSTs above 26 degrees Celsius have also expanded polewards. In direct contrast, the constant greenhouse gas simulation over the same period produced no consistent trend in any of the above categories, but provided a large amount of information on TC natural variability that will be discussed briefly.