Does climate change also change the cyclone risk in Australia?

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Does climate change also change the cyclone risk in Australia?

It has been a while since Brisbane in Australia was last hit by a severe cyclone. But steadily increasing value concentrations and climate change are raising the probability of more extensive wind damage in the region.

Greater Brisbane in Australia is constantly exposed to the risk of tropical storms  and their outer bands. With its high concentration of values, this makes Greater Brisbane one of the regions with the highest loss potential. Though most major storm events have so far been confined to the northern part of Queensland, Brisbane has still had several uncomfortably close brushes with strong cyclones. Furthermore, as climate change takes hold, the Queensland region is expected to see an increase in long-lived cyclones which will increasingly shift southwards. According to current climate research, the number of storm events is likely to decrease, but their severity increase. Based on these indicators, the possibility of a major event in and around Brisbane does indeed exist.

Cyclones in Australia - major losses in the 1970s

In recent decades, very few cyclones have made landfall in Greater Brisbane. Nevertheless, there is an ever-present possibility of a powerful storm event. For example, the region experienced several very heavy storms in the 1970s. In 1972, Cyclone Daisy resulted in an insured loss of A$ 116m in the Brisbane and Gold Coast region. In 1974, Cyclone Wanda caused insured losses amounting to A$ 2.6bn. Zoe followed soon after with an insured loss of A$ 171m (all figures indexed to 2011, ICA).

Area affected by tropical cyclones in Australia and New Zealand

Source: NATHAN Risk Suite

Such events are rare because of strong westerly winds along the latitudes of Brisbane, which break down the vertical structure of a cyclone. However, the precondition for the development of a tropical cyclone, namely a high temperature of over 26ºC in the ocean's surface layer to a depth of at least 50 metres, also exists south of Brisbane in summer. This situation can not only promote the development of a cyclone, but also help to sustain an approaching one. In other words, local winds at higher altitudes need only be weak, for example due to a southward shift in the west wind zone, for a severe cyclone to develop and make landfall in the region around Brisbane.

With wind speeds exceeding 250 km/h and wind fields up to more than 500 km in diameter, cyclones make landfall in coastal regions. Here is how a cyclone develops its destructive force.

Dr. Astrid Zwick und Stefan Lämmle, Munich Re.

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