In Australia, we tend to see a lot of these,
bushfires.
Yeah, we're one of the most fire
prone countries in the world
seeing around 45 to 60-thousand bushfires every year.
But have you ever wondered how or why bushfires start in the first place?
Let's find out.
Perhaps a good place to start is to understand what fire is.
To exist, this wavy, hot, thing actually relies on three ingredients.
Heat, oxygen and fuel. What's fuel?
Well, it’s basically anything that burns.
And when these three things combine it causes a special
type of chemical reaction called combustion.
This reaction usually releases heat and light,
which is the flame thing. And because heat is both an ingredient and a product,
fire is a self-sustaining chain reaction
that continues until it runs out of fuel or oxygen!
So basically, a fire needs a spark.
But how does that happen somewhere like here?
There's many factors for how bushfires start.
It can be deliberate arson, a lot of it’s carelessness.
The other big cause of bushfires in Australia is dry lightning strikes [sound of thunder].
Honestly I would say, the majority of fires are because of humans.
And because our continent is so hot and dry and prone to drought, meaning there's not a
lot of moisture in the environment, it makes it a lot easier for fuel to ignite and burn.
We have a lot of bushfires in Australia, because the landscapes evolved with fire,
we tend to have relatively wet winters
and then during the summer months as things
dry out you've got vegetation that becomes flammable and ready to burn.
So how does a fire spread? Well, a lot of it has to do with the vegetation,
the weather and the shape of the land.
Hey Robbie, how are you going?
But to understand this better,
I caught up with Robbie who's a rural firefighting training officer.
So um, what do we have here?
Okay, so this is a um, burn table. We use it to teach our students a bit about fire behaviour. So,
say a lightning strike, there's no wind here in this situation, so the fire’s just going
to burn out in a sort of circular pattern. Now the other thing that can affect fire,
the two main things, is the wind or slope. So, what I can do here is light another fire on a
20 degree slope and we see, this is where we lit the fire, and we see how we’ve actually
got about 3 or 4 times more distance than this side than the backing or the flank fires.
So, can you explain why fire travels faster up a slope?
Yeah, certainly that's a good question. When you have a fire being up slope,
the heat coming off the fire actually pushes through the fuel
in front of the fire and therefore that accelerates the fire of that direction.
The shape of a fire and how many there, are can also influence how a fire might behave.
The flames are pretty high!
Absolutely, so that's where we're saying,
because it's a line of fire for one thing and the slope, means the fire behaviour,
the intensity is going to be quite large, so you can see the lengthening through there,
that’s all the preheating happening that we talked about before, and so that accelerates the fire up.
Why do the flames react that way in leaning into each other?
It's called junction zoning, basically what happens is that the convection pulls together,
so instead of two separate convection columns,
we have them both join together so that it doubles the, the intensity. And there goes our fire.
I'm glad it's only that size.
Robin: Yeah.
Yeah, luckily this fire was in a controlled environment. But if a fire was somewhere like
here and we added a bit of wind, well it would be a different story.
You see, strong winds are another big reason to how bushfires spread
because by providing more oxygen, it increases
the intensity, and a change of wind direction can make the fire a lot bigger really quickly.
Yeah spot fires galore down here. We’re talking about 60 to 70 metre flame heights,
60 to 70 metre flame height.
In some cases, bushfires can get so big and generate so much power,
they can even create their own weather.
In what the fire is doing is it's producing enough energy in an unstable atmosphere,
that the fire’s convection column or the smoke plume grows vertically. And then,
the fire can actually generate a fire thunderstorm cloud over the top of it.
And in the extreme events, of course, we can see these fire generated
thunderstorms or Pyrocumulonimbus clouds can actually ignite new fires downwind.
Another fire spreader are embers, which are burning materials like leaves, twigs and bark,
and can start spot fires kilometres away. Not to mention the radiant heat that comes
from a bushfire. It can be so intense, that the fuel around it can self-ignite.
If they're particularly dry and fine fuels, they will start to burn themselves. So that is one of
the ways the fire accelerates, it's also what makes it so dangerous for us and for animals.
So, with all this in mind, how do we manage or prevent bushfires?
Well, one way is to quite literally fight fire with fire.
We see this with prescribed burns,
which involves strategically setting planned fires to reduce the amount of fuel in the
landscape, something that's been practiced in Australia for tens of thousands of years.
Cultural burning, it's the First Nations Aboriginal people,
Indigenous people's way of burning the Country.
We call it cultural because it's a part of the culture of the land and the people's
relationship. Culturally we try and keep the fire intensity quite low, because we want to protect
the canopy and if we do our burning early in the cooler times when the lightning strike, the fire
won't be so bad because we've done all that good fire, or that cultural fire around the landscape.
You see, unlike hot fire, which can kill plants and cause thick,
hazardous regrowth, cool fire gently removes fine fuels at lower temperatures,
propagates fire-dependent plant species, and allows animals to safely move away from the heat.
So there's a lot of work that's happening across Australia at the moment in Indigenous fire regimes
and trying to say how can we actually put good fire low intensity fire back into the landscape
and make sure that we're nurturing the landscape instead of letting the fuel loads accumulate.
There are a lot of things we can do too, like keeping fuel loads low around the house,
avoid doing activities that could cause an unwanted fire,
paying attention to weather conditions, and if you're in a bushfire prone area, having
a bushfire survival plan so you know exactly what to do if you need to get to a safe place.
This is a this is part of how we live and where we live. We learn about the science so that
we can look after things properly, so that we can make good decisions so that we can provide
appropriate warnings and advice to communities for how to keep themselves safe to make predictions,
and that's why it's important we understand the science of bushfires.