[LINK] Bush Fire Speeds (was Re: home emergencies)

[Robin Whittle]

(Please note, I have no expertise in this area.)

Regarding bushfire speeds, when the temperature is 46C (~5 or 6%
relative humidity) and there is a strong wind dropping embers several
km ahead of the firefront, I imagine the maximum speed of fire
propagation would be close to that of the wind.

In principle a fire spreading by radiant heat in the crowns of the
trees could spread at almost any speed.  With high enough
temperatures and closely packed eucalypt or pine trees, I could
imagine huge areas - spanning many kilometres, going up within
minutes.  There is plenty of that sort of forest in the central
highlands of Victoria.

Please take a look at:

  http://en.wikipedia.org/wiki/2009_Victorian_bushfires

There is a chart there or wind speed at the Fawkner Beacon, in Port
Phillip Bay for 7 February 2009.   The average speed was about
50km/hr for most of the day.

You can see a temperature chart of that day too.

Detailed temperature charts for the whole heatwave period are:

http://commons.wikimedia.org/wiki/File:Melbourne-temp-2009-02-10.png
http://commons.wikimedia.org/wiki/File:Melbourne-temp-2009-02-10-compact.png


I added some links to the 2009 Victorian bushfires page to animated
archives of weather radar images, but after a few days, this section
was removed.

http://en.wikipedia.org/w/index.php?title=2009_Victorian_bushfires&oldid=270380017#Weather_maps_and_Weather_Watch_Radar_images

The animations are:

http://radar.strikeone.net.au/?fuseaction=loops.main&radar=513&numberofImages=10&dateStart=1233969600&dateFinish=1234005600
http://radar.strikeone.net.au/?fuseaction=loops.main&radar=023&numberofImages=10&dateStart=1233969600&dateFinish=1234005600


While there are some gaps in both sequences, and while the radar
shows the clouds above and downwind of the fires, rather than the
fires themselves, it can be seen how rapidly the fires spread.

There was the Kilmore East fire and one near Buxton - which started
near the Murrindindi Mill.  There are reports of a fire starting in
the Kinglake area too, due to fallen power lines.  So there are at
least two and perhaps three or more sources of ignition for the
fires just north-east of Melbourne.  These were when the Melbourne
temperature was 45C or above.


The Forest Fire Danger Index (FFDI) prediction for Victoria is here:

  http://www.bom.gov.au/products/IDV18500.shtml

I read in The Age recently that 25 and above is "high" and that at
Kilmore East, on 7 February, the FFDI was 180!  There was a
suggestion of new categories for these higher figures, including
"catastrophic".

I haven't yet found archives of the FFDI predictions, or the
algorithm by which the figures are determined.  However, my guess is
that once the temperature gets to the mid-40s, every extra degree
makes the risk grow exponentially.  This is because there are several
factors, presumably multiplying in some way, and these factors tend
to go up together: dryness of the ground and vegetation, high air
temperature, low humidity, strong north to north-west wind due to
there being a high to the north-east of Victoria.

Since we can't be sure how high the temperature will be in the years
to come, and since I think there could be multiple days of 45 or more
each fire season in Victoria, I doubt there is a reliable way of
predicting maximum speeds of bushfire in any forested area of Victoria.

I heard on the radio someone from the Kinglake area saying they were
going to defend their house, but decided to leave when the fire got
within *15* km.  That is a long distance, I think.  In the 15 minutes
they spent packing things into their car, the fire was upon them.
(60km/h)

I have no expertise in this field, but my guesses include:

   Extreme fire danger due to weather and arsonists will continue
   and worsen.

   Traditional methods of defending a house against ember attack
   or an understory fire can't be implemented reliably or safely
   when there is a fire-storm of embers being blown into broken
   windows, under the house etc. and when the radiant heat,
   smoke and lack of oxygen makes it impossible for anyone to be
   outside trying to defend the house.

   Clearing trees for 50 metres or so would help to some extent -
   but many people don't want to live like that, including due
   to lack of shade anywhere near the house.  Also, if everyone
   did that, in some areas there would be little forest left.

   Living in or near a forested area in Victoria means that
   there is a significant risk the house will be destroyed
   in conditions which make escape or survival on the surface
   impossible.

   Therefore, if people want to live in or near the forest
   - and I am not suggesting they shouldn't (I would like
   to) - then they need to regard the house as probably
   doomed if there is a fire during extreme conditions
   like we had on 7 February.

   Therefore, every home - or group of nearby homes - should
   have a reinforced concrete bunker, with a fireproof door
   shielded from radiant heat, with an oxygen bottle and
   enough oxygen masks to go around, water, food, first
   aid supplies etc.

   Everything on the surface - cellphone base-stations, telephone
   cables etc. is likely to be destroyed.  So I guess this
   leaves 27MHz AM or FM VHF walkie-talkies as the best kind
   of emergency communication system.

   An early warning system would be something different -
   perhaps based on cell-phone infrastructure, such as a GSM
   device for receiving calls and activating a siren or whatever
   - since people could be outside or far from the house.

I guess the people of Kinglake, Murrindindi, Narbethong, Marysville
etc. don't need to worry about the worst kind of forest fires for
another few decades.  Now we know what can happen in a few minutes or
hours at 46C, I think everyone in an un-burnt area faces ongoing danger.

We are currently in the La Nina part of the El Nino cycle:

  http://en.wikipedia.org/wiki/El_Nino

This is when things are "supposed to be" cooler and wetter.  However,
for south-eastern Australia, we are no longer getting the rain we
used to get during the La Nina part of the cycle.

I wish I could be optimistic about the survival of the forests and
towns in forested areas in Victoria - but I can't.

  - Robin