Thanks Mike, and thanks for everyone for coming along.
I guess what I want to talk about today is just what real bushfire has it is, and it's
some of our learnings I guess from some recent events, but also something that we've known
for a long time, but has some serious implications if we don't fully understand it.
The first thing I guess to get clear is where does the energy from the fire come from?
And the three primary sources that drive the fire if you like, the fuel, and that's the
obvious one, and that's where a lot of the debate sort of hinges around that if we manage
the fuel we manage the fire.
We also have to appreciate that a lot of the energy of a fire is coming from the weather
itself, so if we don't have severe fire weather we're not likely to have severe fires even
if the fuel is present.
And likewise topography, and this makes a big difference if you're living in hilly terrain
compared with if you're just living in the plains on flat ground.
So the topography enhances or makes more efficient the whole combustion process, and so in Australia
one of the major factors that drive fires is the spotting process, and I'll come back
to that, and topography plays a big role in that.
On the other side of this energy equation is the moisture which tends to dampen down
the process, it absorbs some of the energy, but of course we know in the middle of a drought
there's very little moisture so the dampening effect is much less, so the energy from the
weather, the fuel, and the topography is given a more free reign if you like.
And the other side of it is the atmospheric stability, all our training tells us that
the instability of the atmosphere or the stability of the atmosphere is really important, but
our models don't specifically take it into account, and it's really important.
It's been a major feature of all our catastrophic events, so we can understand atmospheric stability
in the sense of like where you have fogs where the hot air has trouble rising, if you like,
or in thunderstorms where it rises very freely, so when you have a fire and a smoke column
that's rising freely, it means all the air is being drawn in at the base of the fire
as well, and that can enhance the winds, and one of the things we've seen certainly in
Victoria on a number of occasions, and as well as in Canberra in 2003, is those winds
are cyclonic, they're enough to snap trees off, or uproot trees, take roofs off houses
and so on, so the wind that's being experienced is not just the wind or the weather, but also
the wind that's been enhanced by the fire, and that only really occurs when we have very
unstable conditions.
So yes, we need to deal with fuel, but we've also got to look at those other predisposing
conditions.
And here's a little graph that I put together, I know it's lunchtime so you should have warmed
up a bit by now, but what this is basically showing on the bottom axis, the x-axis, is
increasing severity of fire weather, the fire danger index, and on the left hand axis is
the intensity of the fire, and one of the things that happens as the fire becomes more
intense, more fuel actually gets incorporated in the fire, and if you look really closely
down the bottom there you see a little dotted line, which is the intensity of the fire that
we can successfully attack the head of a fire, and you see that under many conditions, under
many fuel arrangements, the fire is well outside our controllable limits, so we have to have
strategies in addition to just straight suppression to deal with those occasions.
The bottom line that I've shown there is basically what happens if you only had six
tonnes per hectare of fuel, which is very low for a forest type situation, but with the
severity of the energy coming from the weather conditions, it's still enough to get it over
that threshold of direct attack suppression, and you see around between 70 and 80 there
where it suddenly kicks up, so the intensity of the fire is enough to actually start capturing
fuels that aren't even affected by a lot of control burning, which might be canopy fuels
or fuels higher up in trees, for example, in a forest environment.
So even though we have lower fuels and it enhances our ability to suppress fire and
it makes them less severe, it still can be beyond the threshold of control and beyond
the threshold where damage occurs, so we just need to be clear about that.
Here's an example, I guess, what happens with the intensity with the increase in ground
slope is almost an order of magnitude between flat ground and really steep terrain in terms
of how intense the fire is, so it's a major contributing factor as well, but it goes beyond
just the hill slope, it's what it does to the fire as well, and I'll come back to that.
And another aspect here is these graphs are showing that the rate of heat output for a
notional one hectare of land, where the blue line down the bottom there is showing what
would happen if you just lit it from a point and let it gradually burn out under a fixed
set of weather conditions, and the yellow line at the other end is the other extreme
where you have massive number of ignition points in that landscape, in this case every
10 metres across the landscape, and the total amount of energy released is exactly the same,
but the rate at which it's released, the power of the fire, is increased dramatically, and
that's what happens when we get spotting, a whole lot of spot ignitions, that's where
we get a firestorm sort of developing, so under exactly the same conditions, if we get those
massive number of embers and spot fires starting, then we get a very different result.
And it's one of the things that was repeated time and again in the Royal Commission in
terms of people's experience of what the fire was like, they had fire coming at them from
different directions, and the fire kept coming at them time and time again, basically because
they were in the middle of this very complex area of fire that had been ignited, not by
a fire front moving across the landscape, but thousands of ignition points.
So just coming back then that spotting is important, and underestimation of the role
of spotting is really quite dangerous both in the sense of how we plan for fire, but
also how we communicate risk.
So what I'm suggesting really is that we need to be thinking about the area of active
fire rather than a fire front, and that changes the way in which we do our research, it changes
the way in which we communicate about fires, we've got to differentiate between the sort
of the more usual fire moving across the landscape as a fire front compared with the catastrophic
events we have where topography is included, where we get this area of fire that involves
averages out the landscape in a way that is not so much of a problem under milder conditions.
This is an example, just a photograph taken down Gippsland in Victoria in January 2009,
so this is before Black Saturday, and what it's trying to depict here, it's pretty clear
that's alright, is a spot fire out in a, it's actually out in a bit of clear pine plantation,
but it's been drawn rapidly back into the main fire front, which you can see off to
the right hand side there, the fire front's about a kilometre away, but the in draft of
air to that main fire front is drawing one of those spot fires back rapidly into that
fire.
A photograph that was taken 30 minutes earlier, the smoke was actually going the opposite direction,
it was being blown by the prevailing wind, but it's now within that kilometre it's been
drawn back into the main fire front, and another spot fire that you can see to the left there
is the smoke from that fire is still being blown forward, so it's outside the influence
of that convective in draft.
So that's just a little example, I guess, of how important this convection column is
and how these spot fires start to play a role.
This is a Churchill fire, and when we're very close to the fire it's difficult to see that
it's actually the area of fire that's contributing, but in fact the heat that's coming off, not
just the flaming zone at the front, but also all the burning wood and heavier fuel behind
the fire front that's adding heat to the convection column is all contributing to really the severity
of the fire.
So this is the same fire, just zoomed out, and what we can see here is this convection
column is effectively helping drag this fire along and holding the fire together at ground
level effectively by pulling the air in.
So way thunderstorms work, we know about downbursts from thunderstorms and so on, the same process
is happening in a fire, and at the top of this you can see a little pyrocumulus cloud
which is actually adding more energy effectively to the fire, helping draw it forward.
So when we look at somewhere like Marysville that was hit by the fire, one of the things
that's quite striking here is that you can see all the trees are still there, they've
got green leaves on them, they've been scorched but they haven't been burnt, and yet all
the houses, well the majority of the houses have been burnt through there.
It hasn't been a big wall of flame that's gone through there, it's been bombarded by
thousands of spot fires, spot fires the embers have set fire to the houses, and the houses
have been the main fuel in this environment here.
So what we're seeing here is evidence of this massive spotting that's been going on, where
are those spot fires come from, largely being launched from the ridge back outside the town.
So typically would think somewhere in a valley is relatively safe because the fire's got
to burn downhill to get there.
That's not the case when you actually scale the fire up and you actually have this massive
area of fire that might be 8 or 10 kilometres across moving across the landscape, it just
gets incorporated in this convective area.
So we're going to run out a bit of time here but I'll try and show a little bit of a movie
here to give you a bit of a feel for what it's like.
This was taken on Black Saturday at Strathewn.
The wind is blowing 60 to 70 kilometres an hour, you look at the smoke there in front
of the fire front, you think there's next to no wind at all.
So the smoke column is effectively blocking the prevailing wind.
So we're down wind here of the fire itself.
The grass fire that you can see in the foreground there, the flame's less than a metre tall.
This is Black Saturday.
We can see the fires got to the top of the Sugarloaf ridge here and what it's done is
launched all these embers and we start to see some of the spot fires going around to
the south here that are just burning initially, they're intense enough but they all start
to develop individually.
But the convection column is influencing all of them.
So this guy's on his own and he's home, he's decided to stay and defend his property, he
considers his area around him as defendable.
And as you look around the landscape here you can see fire in the landscape, it's not
just some big wall of flame that's moving across here, Strathewn, Strathewn you might
remember it's one of the areas that was hardest hit in this fire.
This fire on average is moving at about 12 kilometres an hour at this stage but it's
not the sense you get when you're actually in it and he's actually at this stage here
he's got fires around him, it's just in the middle of some unburnt area at the moment.
So what we're starting to see now, some of those spot fires that weren't doing much before
are now starting to join up, starting to coalesce and every time those fires start to coalesce
their intensity is greater than if just a fire was moving through there on a single
front.
You can see the smoke being drawn back now, it's going from left to right, that's actually
against the wind, it's being drawn into the main fire front.
In Canberra you might remember there was quite a significant fire storm, here we can see
this smoke cloud, this smoke seeing how it's starting to rotate, that was potentially the
starting of a major vortex but in fact collapsed and fell over, so here we see the flame sort
of flaring several tree heights.
He told me he deliberately didn't make too many comments to the top.
Now the impression you get here is that the fire is actually passing to his south, what
we're looking at, we're looking towards the south now, you get the impression that the
fire is actually passing to his south and I'll just stop it at this point and show
you some modelling work that we did that helps explain what was going on here.
So the range to the right is the Sugarloaf range where the fire's got to the top, Jim
Baruta's property who was taking the camera, the video footage is this house down here
on the bottom right hand corner and what we can see, the fire looks as though it's going
to the south and eventually gets him, this is covering about an hour period of the fire
generally but you can see it's quite complex, lots of spot fires that are moving across
the landscape.
This exact same footage, modelling process we'll look at zoomed out a bit to get a better
picture of what the fire's generally doing, so now Jim Baruta's house is at about that
point there, what you can see is actually smack bang in the middle of the fire, it's
not the impression you get from the video footage but if you look very closely at what's
happening here, yeah it does initially go to the south, this is covering about an hour
and a half period, this little bit of replay, so this is his house just there, so he's
actually being surrounded by the fire and so you can get the impression how people talk
about being involved in the fire for a two or three hour period.
So we've got to appreciate fires have different scales and the factors that are important
to fire behaviour at those different scales changes over time, what's important when the
fire's first starting becomes far less important once the fire is large.
A lot of our thinking, a lot of our planning, a lot of our training, a lot of our building
regulations are based around this sort of area here which is somewhere between the crown
fire and the intense surface fire, but the trouble is most of the damage is done, probably
more than 90% of the life and property loss is occurring during these blow up conditions
and we haven't really described that extent terribly well.
So our warnings need to be thinking more about the scale of the fire and how that's
important and that will depend on the nature of the topography you're in.
So if you're in the Adelaide Hills your situation is very different to if you're actually on
the air peninsula for example where there's not much topography.
You need to make a distinction between how much the topography is going to add to the
fuels and the weather situations.
We need to consider all the sources of energy, not just the fuel.
So we've got to think about how severe our weather conditions are as well as the topography.
And we need to think about how big an area can get trapped if you like in the area of
fire and I'm suggesting for a ballpark figure we ought to be thinking of an area about 8
to 10 kilometres in extent if you like for a fire moving once it's well developed.
It might take two or three hours to develop to that size but once it's fully developed
in the first couple of hours it's a more typical fire if you like.
And I guess rather than being totally pessimistic about all this the defensible space and hazard
reduction still is important and provides benefit but we need to put it into this broader
context of how fires are behaving.
So I think I'll just leave it there for now and I'll just have a go.
