Friday, January 10, 2020

A trap with bushfire area statistics in Australia

While discussing the current very bad bushfires in Australia, I have been getting into comparisons with the areas burnt in previous years. This year is very large - currently often quoted as about 10.7 Million hectares. That is huge relative to some previous bad years - eg 1939 at 2 M ha. But I sometimes encounter claims of other monster fires in the past. One is the bogus 5 M ha attributed to the 1851 fires in Victoria. But another one I encountered was the claim of 117 M Ha in 1974/5 at Roy Spencer's blog. These do seem to dwarf the present fires.

Now I had encountered this year in fire statistics before. 1974 was a very wet winter in much of Australia, and in the following December, there were large fires in western NSW, an arid region, where the unusual winter growth burned vigorously. There is a contemporary account here. The area was quite large, 4.5 M ha has been quoted, and homes were lost and six people killed. So I thought that was what is meant.

But Roy Spencer quoted over 100 M Ha. The total area of NSW is 81 M ha. California and Texas together are about 108 M ha. I didn't believe it. But he had a plot of Wiki data:





and indeed the table did list numbers like 45 M ha for the Northern Territory in that year, total 117 M ha. Now I remember the NSW fires, but I didn't remember any stories about such a huge conflagration, which as they noted, is about 15% of the country.

One source quoted was this report to the Government following the 2003 fires (a sort of poor man's Royal Commission). I was at this stage being harried by commenter harry at WUWT, who helpfully pointed to this document, which was part of the Commonwealth Yearbook for 1995 (ABS). Now I am not a fan of these government stats sources for this sort of data, since I don't think they do much scholarly inquiry, but just take figures at face value. But this was marked as contributed by Phil Cheney of CSIRO, who I used to know by reputation, who was a doughty warrior for prescribed burning. So there should be something to it.

"harry" then pointed me to this informative document about NT and in particular its savanna fires. I knew these were regular and large, but I did not realise how large, or at least how large were the quoted areas. It did say that 45 M ha were burnt in 1974. But it also gave this table of particularly large fire years:



So 1974 was large, but not exceptional. That is why I hadn't heard of it. But now there is a curiosity. The 45 M ha for 1969 would also easily qualify for the Wiki list of big fires, as would the other years. But as Roy's graph shows, 1974 stands alone.

I think this probably does come back to Phil Cheney's doc, and indicates the haphazard way these numbers are collected. I think Phil was just using 1974 to illustrate how the northern savanna burnings were large but different to the forest burnings. But it is a number, and so it goes into collections like Wiki's. He didn't mention 1969, so it doesn't.

I looked up more references on savanna regions. This paper gives some general averages:
StateAnnual average area burnt M ha savanna
NT18.1
WA10.6
Qld8.56

And there is the dilemma. These numbers would dwarf most years of temperate forest burning. But that is what we want to know about, so they must be separated. This is not being done systematically. In particular, there is the random inclusion of savanna data for 1974/5 in the Wiki list.

Wiki gives 10.7 M ha as the area burnt by the current season's fires. That does not seem to include savanna, but one has to be vigilant, and a further complication is that some of the forest fires have been close to the tropic in Qld (even Mareeba is mentioned).

Anyway, I think the message for the moment is to be aware of the distinction between temperate forest fires and the fires of the savanna, and also the occasional flare-ups in the arid regions, which are really something different. I hope Wiki will wake up to this too.







15 comments:

  1. > I hope Wiki will wake up to this too.

    Wiki is discussing it: https://en.wikipedia.org/wiki/Talk:Bushfires_in_Australia#1974-75_NT_fires

    ReplyDelete
  2. The timing of the fire "season" also differs dramatically around the country of course

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  3. What's fun about harry, et al at WUWT is that when 'gov't figures and sources' are used to back up their claims they are all excellent figures/sources, but when 'gov't figures and sources' like surface temps, etc don't back up their ideology and claims then those figures/sources are now 'fudged' and inaccurate, and equal a global conspiracy!
    Accordingly WUWTers don't know if they're coming or going.

    ReplyDelete
  4. Nick, good points and information. I would also be curious to know how much of the burned area totals was from controlled intentional burns or if that is counted separately. I suspect there may be difficulty in separating burned area by forest and savanna, especially in the past, because some of the large fires may have burned both. However, this distinction could be made using land use maps before and after, at least for more recent fires where the burned area is well documented and where land use information is available and regularly updated.

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    Replies
    1. Bryan,
      I think in the savanna, no one tries to control them at all. Many are deliberately lit, but this isn't regarded as a terrible thing, so no-one really knows the breakdown.

      I think the main practical distinction is whether anyone tries to put them out.

      Delete
  5. The problems with Dr Spencer's article are being discussed here. https://www.facebook.com/CraigKellyMP/posts/1391555647705732

    ReplyDelete
  6. Off-topic: Hi Nick, I see you are engaging with Viscount Monckton et al over at WUWT and explaining (yet again) scenarios and projections. You might like to check out which Scenario His Lordship is quoting as 'midrange' (no such thing) from IPCC 1990. He usually cherry picks Scenario A (out of A-D), which as in turns out overestimated forcings. The actual forcing trajectory tracked somewhere between B and C, and the associated temperature projections were pretty good. Back in the day (2015ish) I pointed this out ad nauseam at WUWT, until my comments quietly stopped being posted.

    https://wattsupwiththat.com/2015/01/28/global-warming-is-still-on-the-great-shelf/#comment-1439373

    Thanks for all your apparently indefatigable efforts ….

    ReplyDelete
    Replies
    1. Thanks, Phil
      Actually, his Fig 1 is taken verbatim from Zeke's paper, so it has that matching of scenarios. And as I mentioned in comments, it actually gives a pretty fair picture. AR1 is running warm, but within error limits. AR2 is warm. AR3 is neither warm nor cold.

      After that, yes, it's just a rehash of older stuff. I don't think too many people read beyond the first bit.

      Delete
  7. Yes, I've (re)done the homework and believe it or not Monckton is purely and simply lying (again).

    Lord M: In IPCC (1990), the models were predicting midrange warming of 2.78 or 0.33 K/decade. By 1995 the projections were still more extreme. In 2001 the projections were more realistic, though they have become still more extreme in IPCC’s 2006 and 2013 Assessment Reports. Terrestrial warming since 1990, at 1.85 K/decade, has been little more than half the rate predicted by IPCC that year:"

    IPCC 1990 (aka AR1):

    Scenario A: "under the IPCC Business-as-Usual (Scenario A) emissions of greenhouse gases, a rate of increase of global mean temperature during the next century of about 0 3°C per decade (with an uncertainty range of 0 2°C to 0 5°C per decade), this is greater than that seen over the past 10,000 years This will result in a likely increase in global mean temperature of about 1°C above the present value by 2025 and 3C before the end of the next century The rise will not be steady because of the influence of other factors"

    "under the other IPCC emission scenarios which assume progressively increasing levels of controls rates of increase in global mean temperature of about 0 2°C per decade (Scenario B), just above 0 1°C per decade (Scenario C) and about 0 1 °C per decade (Scenario D) "

    But if you look at either the CO2 concentrations or the GHG forcing in Table 2.7, page 57, Scenario A was higher than actual observations. The IPCC projected net forcing of 2.95 w/m2 in 2000 and a whopping 4.59 by 2025. The actual figures (NOAA data) are 2.48 in 2000 and 3.01 in 2016. So Scenario A forcings were just under 20% higher than reality, and reality did not reach the year 2000 projection until 2014.

    Scenario B had 2.77 w/m2 in 2000, 3.8 in 2025, Scenario C was 2.74 and 3.63 W/m2. Still slightly higher than reality, but a lot closer than Monckton's favourite.

    He knows all this: here's a quote "I had not recalled that IPCC had made its 1 k by 2025 prediction under Scenario A. However, Scenario A was its business-as-usual scenario, and it had incorrectly predicted a far greater rate of forcing, and hence of temperature change, than actually occurred."

    https://wattsupwiththat.com/2015/01/16/peer-reviewed-pocket-calculator-climate-model-exposes-serious-errors-in-complex-computer-models-and-reveals-that-mans-influence-on-the-climate-is-negligible/#comment-1431531

    Round we go again ….https://moyhu.blogspot.com/2017/04/gwpf-international-temperature-data.html?showComment=1493336176564#c2358029438803065329

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  8. It is not just the NT fires that make 1974 look so big. The East of Western Australia and the North West of South Australia (both sparsely populated areas) also contributed substantially to the total,

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  9. FYI, there's some problem with the HTML on the "Latest Ice and Temperature Data" page. All the links go to https://www.blogger.com/null. I notice there's also a stray "<" at the top, before the link to "Introduction" ... might have something to do with it.

    ReplyDelete
    Replies
    1. Thanks, Ned
      It seems to be a problem with the Blogger interface. I'm working on it. Quite a few things are messed up

      Delete
    2. Fixed, I hope. Some local internet troubles messed up some uploads.

      Delete
    3. Thanks! Yes, things seem to be working.

      Delete

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