Atmosphere Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Dr Peter Manins, Environmental Consulting and Research Unit, CSIRO Atmospheric Research, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06746 9
Climate Variability and Change (continued)
Tropical cyclones [A Indicator 1.8]
Tropical cyclones affect the north-east, north and north-west coasts. The formation of tropical cyclones and their tracks are influenced by ENSO: more tropical cyclones tend to form in the Australian region during La Nia years than in El Nio years. Tropical cyclones tend to strike the eastern Australian coast more frequently in La Nia years and tend to move away from the continent during El Nio years. Although the total number of cyclones has decreased since 1969 to 1970, the number of intense cyclones (minimum central pressure <970 hPa) has increased, although neither trend is statistically significant at the 95% confidence level (Nicholls et al. 1998) (Figure 40). The decreasing trend in total cyclone numbers may be associated with a decreasing trend in the SOI, due to the increased frequency of El Nio events from 1980 to 2000. Although there are small difference among the trends in numbers of the three subregions around Australia, a downwards trend is seen in all three regions (Figure 41).
Figure 40: Total number of tropical cyclones (teal bars), and the number of intense tropical cyclones (yellow bars) in the Australian region (105-160E).
An intense tropical cyclone is defined by a minimum central pressure of <970 hPa.
Source: BoM
Figure 41: Occurrence of tropical cyclones over northern Australian waters and in three subregions around Australia.
Linear trends in total tropical cyclones are also shown by regression lines.
Source: BoM
Implications
In some model simulations of global climate, tropical cyclones tend to form and travel further south under enhanced greenhouse conditions. There are also indications that tropical cyclones could become more intense. However, most of the global climate models do not adequately simulate ENSO characteristics, which are important for the formation of tropical cyclones. Despite this caveat, the location of tropical cyclones could be quite sensitive to changes in large-scale climate under enhanced greenhouse conditions, with major implications for coastal zones.