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A history of vulnerability: putting Tasmania’s bushfires in perspective

Once again, bushfires are laying waste to Australian homes and communities, this time in Tasmania, with reports of 65 or more properties destroyed in Dunalley alone. Fire emergency services in other states…

The town of Dunalley in south-eastern Tasmania was ravaged by bushfires. AAP

Once again, bushfires are laying waste to Australian homes and communities, this time in Tasmania, with reports of 65 or more properties destroyed in Dunalley alone. Fire emergency services in other states are also on alert as the country bakes in sweltering heat. Fortunately, at the time of writing, there has been no reported loss of life.

Bushfires are the downside of the desire of many Australians to live close to bushlands. Concerns that global warming will aggravate this downside risk are repeatedly amplified through the media and blogosphere:

No weather event can conclusively be linked to climate change, but it is worth noting that the frequency of extreme events like these from now on will have to be accepted as the “new normal”.

The first phrase is certainly true, while the second presumes a degree of clairvoyance not accessible to most scientists.

It still is too early to know how the remainder of the bushfire season will play out, but this doesn’t stop us from putting the history of bushfires in Australia into some perspective.

In what follows, we try and make sense of the real risk as revealed by the cold reality of data unfettered by prejudices and biases. For bushfires, the factors that can be analysed with some objectivity are exposure and vulnerability, essentially the disposition of homes vis-à-vis the bush, and fire history.

Exposure and vulnerability

The single variable that explains most of the vulnerability of a home to bushfire is its distance from the bush. Research conducted by Professor John McAneney and Dr Keping Chen in 2004 and 2010 mapped the location of houses destroyed in some major historical fires and their distance to the nearest bushland interface. They estimated for the Royal Commission into the 2009 “Black Saturday” Victorian fires that historically about 85% or more of the properties lost since the 1967 Hobart bushfires were located within 100 metres of the bush. They found no record of buildings further than 700 metres being lost to bushfires, even though we know embers can travel much further than this.

The likelihood of a property being destroyed in a fire if located within 50 metres of bushland under extreme fire weather conditions is around 50-60%. For homes within 10 metres of bushland in Marysville and Kinglake during the 2009 Victoria Black Saturday fires, it was around 80 to 90%. Some 60% of all homes destroyed in these two towns fell within this distance category (less than 10 metres).

Using nearest distance to bushland boundaries as a measure of exposure, we estimate that around 34,000 addresses in Tasmania lie within 100 metres of the bush, approximately 11% of all addresses in the State. Figure 1 shows the distribution of numbers of addresses by distance to bushland in the entire State, whereas Figure 2 shows our best understanding of the disposition of homes in Dunalley.

Figure 1: Numbers of addresses categorised by distance to bushland boundaries in Tasmania.

Risk Frontiers

Figure 2: Dunalley, Tasmania – Bushland delineation (green lines) and location of building address points.

Risk Frontiers

The exposure metric we defined here is not the only factor to determine the bushfire risk: we also need to consider the likelihood of having the right weather conditions, of ignition to occur, and so on. These factors are not easily quantifiable as some depend on human behaviour, the serendipity of putting down fires in their early stages, and so on.

History does not repeat itself but, as Mark Twain said, it rhymes, and so it is useful to examine the historical record to identify the patterns of bushfire losses in Australia.

History

The first reference to bushfires in Australia by European explorers was registered in Abel Tasman’s diary on the December 2 1642 during his exploration of Tasmania’s east coast. Fires are natural to the Australian landscape. Its native biota has evolved in and is adapted to fire conditions. Viewed from this perspective, human settlement is the aberrant factor to Australia, not fires.

To build a long-term picture of the historical losses for Australian bushfires, staff at Risk Frontiers have searched reports in early newspapers and other documents including police and coroners’ reports left to us by our forefathers. Since 1994, we have developed a database of past natural hazard events that caused either loss of life or property, or both.

This database is called PerilAUS and is reasonably complete for bushfire losses. Table 1 shows the breakdown of 14,000 home losses by state since 1926, the first major loss event of the 20th century.

Risk Frontiers

The state of Victoria has borne the greatest share of the destruction, in spite of not having had the largest number of events. Tasmania lies in third place in terms of number of properties lost, mainly because of the 1967 Hobart fires, when more than 1550 houses were destroyed.

The numbers in Table 1 reflect raw numbers as recorded at the time. Since then, the population has obviously increased, as has numbers of exposed properties. These changes were analysed by Crompton et al with the results before and after normalisation shown in Figure 3. The normalised figures indicate the likely losses if all fires had impacted upon 2011 societal conditions — an apples-by-apples comparison. The normalised figures show no long-term upward or downward trend. (Interestingly, this is also the case for some 30 similar normalisation studies of economic and insured losses from various extreme weather events and in different countries.)

The main finding of Crompton et al is that the trend of increasing numbers of buildings destroyed (before normalisation) in bushfires in Australia can be explained by an increased population that chooses to live near bushland.

Figure 3: The top graph shows the aggregate number of homes destroyed each year, while the bottom graph has been adjusted to account for the increase in the number of buildings since the original event.

The stars in Figure 4 show the locations of historical fires in Tasmania that caused property losses. These have tended to occur more often around the Hobart region, where most people live and more vulnerable properties are located.

In conclusion, we show that from an historical perspective there’s nothing new about bushfires in Tasmania, nor the potential for large losses. It was only a matter of time until the conjunction of bushfires and home destruction occurred.

We do not yet have a complete picture of the events that have unfolded in Tasmania, but will be keeping a close watch.

Join the conversation

37 Comments sorted by

  1. Christopher Johnson

    Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania

    This is an interesting analysis. But can you take account of the fact that, other things being equal, the normalised number of houses lost ought to have gone down during that period, because we have seen major improvements in bushfire prediction and fire fighting (better communications, better gear, helicopters, a lot of research on fire behaviour etc).

    It might be a sensible conclusion that because we have not seen that expected fall, there has been an offsetting increase in fire danger.

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    1. Felipe Dimer de Oliveira

      Risk Scientist at Macquarie University

      In reply to Christopher Johnson

      The historical loss record is really driven by episodic and large loss events that occurred under conditions where the fire response teams can do little to affect the final outcomes.

      Nor it is a given that improved technology will aways decrease the vulnerability of properties if land use planning practices encourage more people to live within or very close to bush lands.

      In the early part of last century people died and homes were destroyed because people were living in the bush often in and around sawmills for example. Today the same thing is happening because of lifestyle choices and compliant land-use planning that allows people to live in dangerous situations given a bushfire.

      We have observed a trend of decreasing fatalities normalised by population over all natural hazards but the 2009 Victorian fires serve as a stark reminder that even with near perfect forecasting of fire weather, we can still lose many lives.

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    2. Philip Dowling

      IT teacher

      In reply to Christopher Johnson

      A simple explanation is an even greater level of risk taking. The traditional farm was often surrounded by a home paddock, and/or garden and/or deciduous trees. Farmers had to plan to fight fires without external assistance.
      In addition, levels of hazard reduction - both official and unofficial - have been reducing.
      At the time of the Victorian fire disaster removal of dead branches was forbidden in some areas. Even the Hume Highway in Victoria had high levels of fuel beside it.

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    3. Aaron Troy Small

      Student

      In reply to Christopher Johnson

      I write as a non-native Tasmanian (I've only been here 3 years or so), but also as a firefighter. One thing I have noticed is that there has been a marked reluctance in some areas to avoid excessive shrubbery around and/or adjacent to property, to clear the under-storey and to live as close as possible to semi- or almost mature native gums and stringybarks.

      Whilst not technically part of the wild "bush", the fact is the fine-fuel load, coupled with an understorey and native canopy makes the correlation…

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    4. Aaron Troy Small

      Student

      In reply to Felipe Dimer de Oliveira

      To what extent is the extensive 'spotting' behavior responsible and is the nature of 'spotting' changing? Is the removal of large trees leading to regeneration (both natural and planned) of species more prone to throwing large, longer lived brands and embers? What effect has the lack of preparedness in some areas has had?* What effect has the choice of shrubs and garden plants had on the volatility of the fuels adjacent to buildings?

      These are all questions which would presumably bear upon the…

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  2. Don Aitkin

    writer, speaker and teacher

    A fine piece with some interesting data, which seem to give a similar picture to the incidence of floods and the destruction they cause. Thank you.

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  3. alexander j watt

    logged in via Twitter

    What an interesting analysis, thank you. Particularly to see that the closeness to bush is such a clear factor in losing homes - on Wednesday even with catastrophic conditions, I think only one house was lost to grass fires.

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  4. Robert Edwin White

    Professor Emeritus

    What a sensible article, reminding us that bushfires are a very natural occurrence in Australia. Our continent has been getting progressively drier and hotter as we have drifted very slowly in a northeasterly direction after separation from Antarctica about 50 million years ago (a process over which we humans have absolutely no control). Add to this that the indigenous people have been managing the native vegetation using fire for the past 40000 years or so. Consequently, our native vegetation has…

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    1. Felix MacNeill

      Environmental Manager

      In reply to Robert Edwin White

      I hadn't forgotten that Australia was prone to bushfires, so I didn't need a reminder of that fact any more than I needed your childish little comment about 'clairvoyants'.

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  5. Murray Webster

    Forestry-Ecology Consultant/Contractor

    This is the same as what I was taught in fire science lectures as part of a forestry degree at the ANU in the 1980s'

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  6. Jon Hunt

    Medical Practitioner

    I live at Belair, in SA. There are lots of trees. The BAL for my property is 19 ( I think; it's one less than fire zone at any rate). My house would have to be the lowest level for the entire suburb because at least I have tried to have a cleared area around the house. As far as I can see no one else has bothered, every other house seems to have trees almost hanging over the roof. So when there is a bushfire, all these will no doubt go, including quite possibly mine. What I find surprising is that people seem amazed that there is so much destruction when a bushfire hits when no one has done anything to mitigate the risk. We seem to have not woken up to the dangerous environment we live in. Why is it we do nothing to reduce that risk through legislation or otherwise?

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    1. In reply to Jon Hunt

      Comment removed by moderator.

    2. Aaron Troy Small

      Student

      In reply to Jon Hunt

      The phrase "'tis always easier to beg forgiveness than gain permission" springs to mind. But please do remember that even a prepared property, with adequate cleared, defensible space, coupled with pro-active and active firefighting by capable adults, is not necessarily ABLE to be successfully defended in some conditions.

      Believe me on this, some fires just simply cannot be stopped regardless of the assets to hand. A small petrol pump, maybe some 1" to 1 1/2" lines (percolating canvas for preference…

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  7. Mike Hansen

    Mr.

    The central claim in this article is nonsense.

    The authors quote the following
    "No weather event can conclusively be linked to climate change, but it is worth noting that the frequency of extreme events like these from now on will have to be accepted as the “new normal”.

    And then smugly state "The first phrase is certainly true, while the second presumes a degree of clairvoyance not accessible to most scientists."

    Sorry no - it does not require clairvoyance - science does the job quite…

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  8. David Legge

    Scholar Emeritus in the School of Public Health & Human Biosciences at La Trobe University

    You take a dismissive (almost sneering) tone to those who fear that global warming might lead to increasing numbers of bushfires, property losses and deaths. You conclude that there is “nothing new about bushfires in Tasmania, nor the potential for large losses”.
    You cite Abel Tasman to argue that bush fires have always been with us in Australia but you do not cite any evidence regarding any changes or lack of changes in frequency, extent or fierceness of bushfires.
    You demonstrate that…

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  9. Mike Hansen

    Mr.

    The authors also make the claim

    "The normalised figures show no long-term upward or downward trend. (Interestingly, this is also the case for some 30 similar normalisation studies of economic and insured losses from various extreme weather events and in different countries.)"

    but provide no reference.

    This is a claim that has been popularised in Murdoch's WSJ by climate science denier/luke-warmer Roger Pielke.
    http://www.skepticalscience.com/wsj-sandy-global-warming-asking-right-questions.html

    It is rebutted by the head of reinsurer Munich Re’s Geo Risks Research unit, Prof. Peter Höppe.
    http://www.munichre.com/en/media_relations/press_releases/2012/2012_10_17_press_release.aspx

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    1. David Legge

      Scholar Emeritus in the School of Public Health & Human Biosciences at La Trobe University

      In reply to Mike Hansen

      Actually ROGER A. PIELKE JR. of the Center for Science and Technology Policy Research, University of Colorado, Boulder, Colorado is a co-author of one of the main papers (Crompton et al 2010) upon which the above blog was based.

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    2. Mike Hansen

      Mr.

      In reply to David Legge

      Thanks David. I should have guessed that the dismissal of climate science as "clairvoyance" meant that Pielke Jr would be involved.

      http://www.sourcewatch.org/index.php?title=Roger_Pielke_Jr.
      "Huffington Post writer David Roberts has argued that Dr. Pielke has "been playing footsie with denialists and right-wing ideologues for years; they're his biggest fans."

      Here is a reply to the Crompton et al 2010 paper from Neville Nicholls, School of Geography and Environmental Science, Monash University.
      http://sciencepolicy.colorado.edu/admin/publication_files/2011.12.comments.pdf
      "The absence of an upward trend in normalized building damage in Australian bushfires may reflect reduced vulnerability (due to improved weather forecasts and other factors) offsetting increases in the frequency or intensity of bushfires."

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  10. Comment removed by moderator.

  11. Jill Sanguinetti

    university lecturer (retired)

    I find D’Olivieria, Macanerny and Chen’s account of bushfire risk simplistic and fundamentally unhelpful – the suggested conclusion is that the only thing we can do is either chop down all bush surrounding towns, or re-locate millions of homes, including farm homes, away from rural areas. Neither solution is feasible.
    For a start, what is achieved by throwing doubt on the impact of global warming on increased fire risk, when this is already settled scientific consensus? There can be no discussion…

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  12. Ben Beccari

    PhD Student in Risk and Emergency Management at Istituto Universitario di Studi Superiori di Pavia

    If we were already seeing a climate change signal in the loss data (which is dominated by events with recurrence intervals of about 20 years - i.e. you need either a big change {doubling or more} or many years of data) with only 0.8C of warming it would be very, very worrying considering at least 2C and as much as 8C of warming could be in the pipeline.

    The fact that increases in exposure and increases in property value drive losses is a bit of a no-brainer. If you're worried about disasters you should be addressing exposure and vulnerability.

    Climate change is concerning for other reasons - the expected losses due to long term shifts, ocean acidification and sea level rise (for agriculture, biodiversity, tourism, fisheries, coastal infrastructure etc.) are all much larger than the impact of any predicted change on extreme weather.

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    1. John McAneney

      Managing Director of Risk Frontiers at Macquarie University

      In reply to Ben Beccari

      In response to Mr Hansen's comments, I refer you to a review by Bouwer (2010) in the Bulletin of the American Meteorological Society:

      http://www.globalwarming.org/wp-content/uploads/2012/11/Bouwer-Have-disaster-losses-increased-due-to-anthropogenic-climate-change.pdf

      This paper summarizes some 21 different studies which all show no increase in histories of economic or insured losses, once these losses have been normalised for known changes in population, wealth and inflation. This is true for…

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    2. Don Aitkin

      writer, speaker and teacher

      In reply to John McAneney

      Thank you again for a sane reply to the ad hominem sledging that so often passes for comment in The Conversation on anything to do with climate change. What on earth does a Huffington Post writer's comment on Roger Pielke Jnr have to do with the argument of the paper above?

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    3. Mike Hansen

      Mr.

      In reply to Don Aitkin

      Roger Pielke Jr regularly inserts himself into the political process in the US testifying on climate change before Congress (He has a doctorate in political science not climate science). Not surprisingly the Republican climate deniers find Pielke's message of lukewarmism ("it is happening but it is not bad") seductive.

      The idea that I cannot mention Pielke's views or how his views are assessed is quite frankly ridiculous. Pielke is a political player who affects via US policy, climate mitigation policy here and globally.

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    4. Mike Hansen

      Mr.

      In reply to John McAneney

      I suggest people read the Bouwer article that you have linked to - that is not the killer paper you claim it to be and it is contradicted by the world's two major reinsurers Munich Re and Swiss Re.

      http://www.swissre.com/media/news_releases/nr_20121219_sigma_natcat_estimates_2012.html
      http://www.munichre.com/en/media_relations/press_releases/2012/2012_10_17_press_release.aspx

      You claim " However there again the literature points to it being a very long time before a climate change signal will…

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    5. Don Aitkin

      writer, speaker and teacher

      In reply to Mike Hansen

      Mike,

      I would not myself regard insurance companies as disinterested judges with respect to natural disasters.

      With respect to what you can mention when you write you are of course your own master. I was only commenting as a reader, and to me what you said about Pielke Jnr came across as sneering and irrelevant — in keeping with your forthright assertion that the central claim in the article above is 'nonsense'. You quote Hansen as the authority, but the paper you cite does not really do the job you ask it to.

      You say that Pielke 'inserts himself into the political process'. Do you mean that he acts as a citizen in a democracy? You do realise that you have the same opportunities in our country to do the same? Why is it wrong for him?

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    6. David Legge

      Scholar Emeritus in the School of Public Health & Human Biosciences at La Trobe University

      In reply to Don Aitkin

      It intrigues me that no one has commented on my criticisms of the methodology underpinning the Crompton et al research upon which this blog depends. Several distinguished folk have commended the authors for their blog, apparently without regard to the quality of the evidence upon which it is based. I speculate that when the publication confirms our prejudices we feel less need to interrogate the methodology.

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    7. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to David Legge

      The fires in Tasmania in 1898 are the worst on record, followed by the fires of 1934. 1967 had the most property damage - hardly surprising, despite being a 'medium' rather than the 'mega' fires of '98 and '34.

      The fires of Tasmania are reconstruct-able by looking at the ages of forests, particularly mountain ash and messmate. These reconstructions take us back several centuries. Hence for people who have actually studied readily available bushfire/ecological research that looks back over several centuries, methodologies that seek to relate property damage to climate change are materially irrelevant.

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    8. Ben Beccari

      PhD Student in Risk and Emergency Management at Istituto Universitario di Studi Superiori di Pavia

      In reply to John McAneney

      Thanks for the reply John.

      One thing often lost in discussions on climate change is talk of uncertainty (noting that risk is all about uncertainty - the greater the uncertainty, the greater the risk and thus calls for action should be greater).

      With the huge noise in the loss data is it possible to put an uncertainty range on the trend lines in the 'raw' and normalised data?

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    9. Don Aitkin

      writer, speaker and teacher

      In reply to David Legge

      You may be right. I read your criticisms, and didn't do other than nod. There are bound to be possible improvements in any paper. But I didn't see your criticisms as destroying the validity of the paper. I have been following the 'normalisation' argument since I first came across it. It is a useful corrective to the notion that every disaster we see is worse than the last one. But it is only an approximation, and no doubt others will improve upon it in time.

      More generally, I have been in the bush often enough, and over a long enough time, to wonder why anyone would live in in an area, even in the wet sclerophyll forests of eastern Australia, where there will, almost inevitably, be a fire that could destroy their house and possibly themselves. I would not plant eucalypts as street trees, let plant them on my land, for the reasons you give.

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  13. Philip Dowling

    IT teacher

    It is good to read a paper which has a clear hypothesis and supporting data.
    Of course, it does not consider all variables, nor does it attempt to do so.
    It is unfortunate that so many apparently educated people seek to use the construct of "climate change" when it clearly violates the principle of Occam's Razor.
    While not a perfect analogy,"the solution" to drowning deaths of young people has been to make more and more rules about pool fences, when other solutions such as emptying or removing a pool when young children can't swim, or teaching them to swim as early as possible are not emphasized. Despite extra regulations, children still drown often because gates are left open.
    Most people who move into sylvan natural settings are more interested in the tweeting of the birds, than the explosive nature of gum leaves in a stream of hot wind.

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  14. Murray Webster

    Forestry-Ecology Consultant/Contractor

    Frankly I find the title of this article arrogant. I understand that academics these days have to grab headlines to try to appear relevant and attract funding, but we do have records of fires in Tasmania going back a couple of centuries using forest age as a dating method.

    I suggest that rather than "A history of vulnerability: putting Tasmania’s bushfires in perspective" the title may be more historically accurate as, "a late 20th century/early 21st century risk analysis of the Tasmanian bushfires"

    "Perspective" is such a relative term....

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  15. Peter Johnson

    Fire Safety Engineer

    A very interesting and useful analysis.
    As a fire safety engineer, we know that distance as well as the area of the "radiator" are two of the key factors in the determination of radiation levels at a target property such as a house. So the larger the area of adjacent bushland, and the shorter the distance away, as well as the "radiator" temperature, the greater will be the likelihood of ignition, depending on the target vulnerability.Presumably there is also a relationship about the volume and temperature…

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