New data has revealed that tropical cyclone numbers have been declining in the Australian region in recent decades, including both severe and non-severe tropical cyclones.

The Bureau of Meteorology’s tropical cyclone database has reliable historical records of every tropical cyclone in the Australian region since the 1970’s. Over this time, there has been a noticeable decline in the number of tropical cyclones forming near Australia.

The average annual number of cyclones in the Australian region between 1981 and 2010 was 10.6. Around half of these (5.5 per year) were severe tropical cyclones, which is category three or above on the Australian scale.

The average number of tropical cyclones inside the Australian region has dropped by around one cyclone per year in the most recent complete 30-year period, from 1991 to 2020.

Severe tropical cyclones have also decreased from 5.5 per year in the 30 years ending in 2010 to 4.8 per year in the 30 years ending in 2020.

This trend of declining tropical cyclone numbers near Australia in recent decades is in line with other studies that link climate change to declining global cyclone numbers on much longer time scales.

One study published earlier this year by Australian scientists found that on average, the global annual number of TCs has decreased by around 13 percent in the twentieth century compared with the pre-industrial baseline 1850–1900. The study also found that the Australian region is observing around 11 percent fewer cyclones compared to the 19th century.

While the exact cause of this downward trend in cyclone numbers is an active area of research, climate change-induced alterations of Earth’s broad-scale atmospheric circulation patterns is thought to be playing a major role.