01 February 2011

Cyclone Yasi in Context

As the incredibly powerful Cyclone Yasi bears down on Queensland, I thought that it might be worthwhile to put the storm into longer term context.  The Crompton and McAneney (2008) paper that I have cited several times of late on normalized Australian insured losses from extreme weather events includes this noteworthy comment:
The average annual weather-related normalised damage over the 40-year period is AUD$820 million with a standar deviation of AUD$960 million. The recent past has been relatively benign in terms of loss activity, with annual damage over the most recent 5 years averaging AUD$420 million, close to half the average annual loss over the entire period of the Disaster List.
In the absence of systematic evaluations of data, it would be all too easy to consider recent experience (whether that be the past week or the past decades) to somehow be "normal" and thus the basis for expectations of the near future. Such expectations, when out of sync with a longer term perspective, can easily lead to misplaced judgments of risk and contribute to poor decision making.

Such a systematic evaluation of the long-term tropical cyclone landfall record in eastern Australia was published last summer in Climate Dynamics by Jeffrey Callaghan and Scott Power (2010).  Callaghan and Power find a long-term trend of much fewer landfalls of intense cyclones (i.e., Category 3, 4, and 5) in the region.  They write:
The linear trend in the number of severe TCs making land-fall over eastern Australia declined from about 0.45 TCs/year in the early 1870s to about 0.17 TCs/year in recent times—a 62% decline.
The figure at the top of this post comes from their paper and comes with the following caption:
Fig. 1 The number of severe tropical cyclone (TC) land-falls in each TC season from 1872/1873 to 2009/2010 inclusive. The corresponding linear trend of -0.0021 TCs/year is also shown. This represents a decline of approximately 60% over the full period.
They find evidence for a relationship between intense cyclone landfall activity and the ENSO cycle, reflecting the natural variability of the system. They speculate about a connection between the significant decrease in landfalls and global warming, but find little convincing evidence of such a link.  They explain:
If natural variability dominates the recent decline, and if this natural variability exhibits low levels of predictability as suggested by the study of Power et al. (2006), then the frequency of damaging land-falls could increase abruptly to much higher values during the coming decade.

On the other hand, some unknown fraction of the recent decline in the SOI might instead reflect a weakening of the Walker Circulation in response to global warming (e.g. Power and Smith 2007). This means that the component of the decline in land-falls linked to the decline in the SOI might also be partially driven by global warming. . .

The extent to which global warming might be contributing to or offsetting the decline in land-falling TCs over eastern Australia is unknown.
Callaghan and Power note prudently that the unresolved issues of global warming need not stand in the way of making effective judgments of risk -- landfall rates have been higher in the past and that observers should not be misled by recent experience:
Given that natural variability is at least partially responsible for the observed interdecadal decline documented here, and that this natural variability might be dominated by unpredictable changes (Power et al. 2006), it would be imprudent to suppose that the very low landfalling rates observed in recent decades will necessarily continue. Planning should therefore reflect the possibility of a rapid return to much higher landfall rates.
Best wishes to all those in Queensland affected by Cylone Yasi for a speedy recovery, and what inevitably will be storms to follow.


  1. Roger, you seem a bit eager. Couldn't you wait with these kinds of analyses after Yasi blows over?

  2. "As the incredibly powerful Cyclone Yasi"...

    I'm not sure about the need for the hyperbole here. Yasi is a strong storm, no doubt, but it wouldn't rank a Cat 5 on the Saffir-Simpson scale. In fact, it ranks as only the 8th strongest storm in the region since 2000. (Anyone interested in the data can find it here: http://weather.unisys.com/hurricane/). Worldwide 2010 saw 6 storms at least as strong as Yasi. 2009 also saw 6.

    Just don't see the need for the word "incredibly" here.

  3. Roger, thanks. What an excellent mine of information you are. So pertinent.

  4. Thanks for this informative post, Roger.

    Interestingly, given the cyclone following the floods, it seems the Queensland government decided catastrophe reinsurance was not worth it:

    The Commonwealth government has already introduced a controversial flood levy to raise $1.6B - controversial because it basically has spent the surplus it inherited on good old Keynesian pump priming projects, some of which are perceived to bear a great deal of resemblance to Lord Keynes' example of painting rocks (ie they should have saved for a rainy day). This news will hardly help the Commonwealth government.

  5. Neven, the Greens saw no need to wait.

  6. The energy from cyclone Yasi could power the world for a year!

  7. And now we have bushfires around Perth.

    Any news yet on the normalized Australian insured losses from extreme weather events?

  8. According to Jeff Masters:

    Tropical Cyclone Yasi the second most damaging storm in Australia's history

    Tropical Cyclone Yasi has dissipated, but the damage totals from the storm make it Australia's second most expensive tropical cyclone of all-time, according to Tropical Storm Risk, Inc. The storm's $3.5 billion price tag is second only to Cyclone Tracy, which hit Darwin on Christmas Day 1974, doing $3.6 billion in damage (2011 dollars.)

    And it doesn't seem to be over yet:

    Victoria swamped: storm wreaks havoc

    Bureau of Meteorology forecaster Terry Ryan said the ''unprecedented'' movement of cyclone Yasi inland to the Northern Territory, combined with a longer cloud band caused by ex-cyclone Anthony, had produced a humid and unstable air mass over Victoria. ''We've never seen anything like it in Australia,'' he said.

    A cold front crossing Victoria was expected to bring more rain before clearing later today, the bureau said.

    The latest storms followed statewide flooding in January that cost an estimated $6 billion in damages and lost productivity, and flash flooding last September.

  9. Here is some more context I thought would fit in well here:

    Suncorp Group chief executive Patrick Snowball has warned that reoccurring natural disasters might drive multinational re-insurance companies out of the Australian market.

    Speaking to ABC TV’s Inside Business, Mr Snowball said that many people in Queensland did not have flood insurance, which was causing re-insurers to avoid targeting the state.

    He said the driving force of premiums in the global re-insurance market was the frequency of natural disasters.

    “We’ve got to understand that if this becomes a year-in, year-out problem, the re-insurers are not going to be looking to their premium being risk mitigation in Australia, they’re going to think that it’s going to have to carry a premium,” he said.

    However, Mr Snowball further said that risk mitigation was just as important for home-owners and occupants as paying insurance premiums.

    Queensland houses need to be built to cyclone standards in order to withstand the weather, he said.

    Suncorp Group, which is Queensland’s biggest insurer, is currently the only provider of automatic flood cover in the area.

  10. Update on Yasi costs:

    "Members of the ICA are continuing to work closely with the QLD Government to work as quickly as possible to complete assessments of insured property that has been damaged.

    The overall impacted properties figure has been significantly revised downwards to 5,900 from initial estimates. It is unfortunate that some commentators in this debate are still reporting grossly inflated and inaccurate figures for damaged properties in order to further their own agenda.

    Whilst it is too early for claims data to be meaningful for Cyclone Yasi it is clear there will be a significant amount of insurance activity arising from the event."