How many more once in a lifetime storms are we going to have this year?, page-17

Tropical cyclone frequency falls to centuries-low in Australia

January 30, 2014

The number of tropical cyclones hitting Queensland and Western Australia has fallen to low levels not seen for more than 500 years, new research published in Nature shows...

Our study shows that current seasonal cyclone activity is at its lowest level in Western Australia since 500 AD and since about 1400 AD in Queensland. That decline began about 40 years ago.

While Australia’s official cyclone records only date back to 1906, we can track cyclones further back in time using measurements of isotopes housed within limestone cave stalagmites. Those stalagmites grow upwards from the cave floor as rainwater containing dissolved limestone drips from the cave ceiling...

The isotope chemistry of tropical cyclone rainwater differs from that of monsoonal and thunderstorm rainwater. As a consequence, it is possible to analyse the chemistry of each of the stalagmite layers, which are approximately 1/10th of a millimetre thick, and generate a record of cyclones over the past 1500 to 2000 years.

My colleague Jordahna Haig then matched the isotope records with the Bureau of Meteorology’s cyclone record over the past 40 years and generated a Cyclone Activity Index, which plots the seasonal activity of cyclones over the past 1500 years.

In the short term, the recent decline in tropical cyclone activity is good news for all those who live in and visit tropical north Queensland and Western Australia...

Several recent studies published in leading journals - including these papers involving the Australian Bureau of Meteorology, Columbia University, and the Massachusetts Institute of Technology - have all separately projected the frequency of tropical cyclones will decrease in the Australian region due to global climate change...

We cannot be sure that this current decrease in cyclone activity is due to climate change - but it is mirroring the forecasts.

Our results also confirm the conclusions of other studies into long-term cyclone behaviour, which show that the past 40 to 100 years of cyclone activity in Australia has been very low compared to times previous...


http://theconversation.com/tropical...low-in-australia-but-will-the-lull-last-20814