Cyclones heading south: Was Marcia just a taste of what’s to come?
CRAZY weather happens in this country. A freak event is usually just that, but after Cyclone Marcia, we have to raise this question.
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CRAZY weather happens. Especially in Australia, it seems. A freak event is usually just that, and climate change isn’t necessarily to blame. But after Cyclone Marcia we have to raise the question: Are cyclones moving further south?
The answer is yes. There have been some pretty hard hitting cyclones in Australia’s history. Tropical Cyclone Tracy flattened Darwin in 1974 and claimed 65 lives. Tropical Cyclone Larry in 2006 caused an estimated half a billion dollars damage. Tropical Cyclone Yasi in 2011 scared the pants off everyone at a very vulnerable time. But this week we saw a new record. “We’ve just had cyclone Marcia cross as a category five near Yeppoon. That appears to be an Australian record for the most southerly crossing of a category five. Whether that’s just part of variability or part of a trend we’ll have to wait and see.” says Steve Turton, Professor of Geography at James Cook University.
We can try to gain some insight into cyclone patterns by looking back into history 60 or so years, to a time when weather data was not as comprehensive but its impacts were felt just as sorely. In February of 1954, a category three or four cyclone crossed the coast at Coolangatta causing a huge amount of wind and flood damage. Strong gales whipped up large waves on the flooded Richmond River in Lismore, NSW. 23 people were killed.
So even before climate change was a thing, it was possible for severe category cyclones to impact south of the Queensland border. With population growth, urban development and coastal living what it is today, a similar impact now would have grim consequences.
“In 1954 the Gold Coast was still basically sand dunes. They didn’t really get developed until the 60s. So the impacts of a similar cyclone today would be very serious indeed.” Says Professor Turton.
When talking about cyclones in Australia, it’s impossible to ignore the west coast, and particularly the stretch between Broome and Exmouth which is more prone to cyclones than any other part of Australia. Significantly, the population in Western Australia increased faster than all other states and territories in 2012 and 2013, with notable growth in the cyclone affected regions of the Pilbara and Karratha. The population increase combined with predictions for fewer cyclones but with fiercer impacts will mean more West Oz locals will bear the brunt of cyclone into the future.
And then there is this other little thing called climate change. In Australia, the climate change debate has produced little consensus but there does seem to be one agreed conclusion. Cyclones, when they form, will pack more of a punch. The Bureau of Meteorology put it in proper Bureau speak; “The number of tropical cyclones is projected to decrease but they may be more intense and reach further south.” So the decrease in frequency of cyclones will, by around the end of this century, be offset by the increase in intensity.
Dr Kathleen McInnes from the CSIRO Marine and Atmospheric Research team sheds some meteorological understanding on the matter. “With climate change, the oceans and atmosphere are warmer, so the atmosphere can hold more moisture which leads to greater rainfall and stronger winds. There are a number of studies that point to slightly fewer cyclones occurring in a warmer climate and that’s because some aspects of the atmosphere that favour cyclones may change in such a way that it will cause less of them to spin up. But when they do spin up the elements will be there for them to be stronger.”
We also have to remember that despite their bad name, cyclones play a very important role in filling dams and breaking inland droughts, and less cyclones will impact water sources, agriculture and eventually the economy.
Less cyclones hitting Western Australia will further exacerbate another climate issue already underway in the south of the state. “The rainfall in South West of Western Australia has declined by about 20-30% since the mid 1970’s and it’s never really recovered” says Professor Tutron. A further drying trend due to the southwards push of the dry tropical region, and less ex-cyclones to drop water on the area will mean added water problems for the agriculture and the ecosystem.
Tropical Cyclone Marcia can’t yet be linked to unquestionable proof that climate change is happening. As the Bureau of Meteorology clarifies, “individual extreme weather events cannot be attributed to climate change without detailed attribution studies, which take some time to complete.” But Marcia can’t be pigeon holed as “just a freak storm” either. Especially if things really are starting to head south.
Last year, Professor Steve Turton in collaboration with Joanne Isaac looked at some of the other impacts of global warming as part of the State of the Wet Tropics 2014 report. Their essay, “Expansion of the tropics” is a follow up to research conducted by the same people five years prior in 2009.
Of the findings, Professor Turton said “It’s not so much a theory, its proven fact actually that the tropics are expanding, and depending on which methods of measurement are used, that expansion is between about 150 and 300 kms every 30 years. That’s an artefact of greenhouse gas emissions so it’s due to human induced climate change.”
It sounds big, and it is. So let’s try to break it down.
1. Climate driven changes may be responsible for the widening of the earth’s tropical zone, which is currently the area between 30 degrees north and 30 degrees south.
2. The estimation of expansion is between 138 to 277km per 25 years.
3. For Australia, this means that the climate boundary between the tropics and the temperate zone will shift south. This then impacts other climate zones. As the tropics shift, the dry subtropical belt will shift south into areas that currently receive sufficient rain for agriculture and water supply.
4. An implication of this is a drying trend for subtropical regions creating problems for water management and agriculture.
5. Further, an expansion in the tracks of tropical cyclones would potentially mean pulling them further south to areas not previously affected by cyclones. This will cause problems for human health, the economy and biodiversity.
So everything is starting to head south, right? Including cyclones?
“With the tropics moving more southward, the changes in the upper atmosphere would create conditions more conducive to cyclone development further south. We have to be thinking that in the future we will get category five cyclones crossing much further south. You could see areas south of Bundaberg more prone to cyclones than they have in the past” says Professor Turton.
As it is, most tropical cyclones tend to get sheared off by strong westerly winds in the upper atmosphere when they get to the latitudes around the Rockhampton region. This weakens the cyclones. But with the expansion of the tropics, the upper winds that essentially blow the puff out of the cyclones will go further south, leaving space for more intense cyclones to roam around in search of warm ocean waters.
“At the moment the sea surface temperatures are warm enough all the way down to the Gold Coast to feed the cyclone but it’s the upper winds that tend to weaken the cyclones. In a warming world those upper wind patterns will shift to create more of a tropical climate in south east Queensland rather than a subtropical climate. And that subtropical zone will push further south down towards the Coffs Harbour area.
Professor Turton thinks building codes in Australia need to be adjusted to meet the changing weather. “Late into this century, I think anywhere north of Coffs Harbour should be looking at having the same building codes that we currently have north of Bundaberg.”
After every major wind event the Australian Building Codes Board (ABCB) send out a team to assess the damage to buildings. They work with the Cyclone Testing Station in conjunction with the James Cook University and are currently studying the effects of Tropical Cyclone Marcia’s 150km/h wind speeds at Yeppoon in Queensland.
“What they’ve found is that new buildings that are correctly designed and constructed in accordance with the national construction code have generally performed very well. The buildings that are pre-1980ish have been found not to perform as well” says Ron Deveer from the ABCB. This is due to a combination of reasons including degradation of building material, white ants, poor maintenance and less rigid building codes.
The change to building standards were implemented after Cyclone Tracy in 1974 when it was clear that new buildings were not withstanding cyclonic winds. “Since then the standards have been upgraded and have proven to be adequate” says Mr Deveer.
Despite possible changes to cyclone patterns in the future, the Australian Building Codes Board insists they are meeting requirements. “At this point in time there is no strong evidence to say that cyclones are shifting further south, but we are constantly monitoring it. Any change to those standards that would significantly increase construction costs doesn’t appear to be warranted.”
Regardless of which side of the fence one sits in the climate change argument, the fact is Australia will see extreme weather impacts again. Some, inevitably, will be bigger and badder than before and others will seem tame in comparison. We know that the impacts of a severe category cyclone, no matter where it hits land, are felt throughout the entire country. So the post-natural-disaster-de-brief is essential for all Australians. What can we learn? How can we be better prepared? How do we adapt to changes in the climate? Debate needs to keep raging.
Originally published as Cyclones heading south: Was Marcia just a taste of what’s to come?
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