Bushfires in Australia
By Mehwish Manzoor

What is Bushfire ?
• A bushfire is a wildfire that occurs in the bush
(collective term for forest, scrub, woodland or
grassland of Australia, New Zealand, New Caledonia).
In southeast Australia, bushfires tend to be most
common and most severe during summer and
autumn, in drought years, and particularly in El Nino
years.

Bushfires in Australia
• Bushfires in Australia are a widespread and regular
occurrence that have contributed significantly to
shaping the nature of the continent over millions of
years.

Why are there bushfires in Australia?
• The whole of the Australian continent is prone to
bushfires.
• This is due to Australia’s:
– hot climate
– low rainfall
– natural vegetation

What factors determine if a bushfire will occur?
• The basic factors which determine whether a
bushfire will occur include the presence of:
– fuel
– oxygen
– an ignition/heat source Heat
Fuel Oxygen

Cont...
• More specifically, fire intensity and the speed at
which a bushfire spreads will depend on
temperature, fuel load, fuel moisture, wind speed
and slope angle.

What conditions lead to extreme fire weather?
• Fire weather is determined by short term climate
variables like temperature, humidity, wind, rainfall and
evaporation that can change during the course of a day
or even an hour.
• There are several factors that combine to create
extreme fire weather. Wind speed is the primary factor
and the temperature and dryness of the air are the
other factors. These affect the moisture content of fuels
such as twigs, bark, and leaves.

Cont…
• The lower the moisture content, the easier it is for
the fuel to ignite and burn. Under the extremely dry
conditions the led up to the Victorian fires, the fuel
was very dry and could burn very quickly.
• Once a fire begins, fire weather and topography
affect the behaviour of bushfires in terms of the rate
of spread, the height of the flames, the intensity of
the heat released and so on.

Victorian Bushfires fast facts
The high temperatures,
some in excess of 45
degrees, and dry air
experienced throughout
Victoria on Saturday resulted
in very low fuel moisture
content.

Cont….
The extreme fire weather conditions that occurred in
Victoria during January and February were partly due
to very high temperatures following a 50 year warming
trend, and very dry conditions following 12 years of
below-average rainfall.

Cont….
• Scientists investigating the Victorian fires will look at
fire behaviour, including how fast the fires moved,
patterns of spread, the conditions under which the
fires were burning and the moisture content of the
fuels.

What causes bushfires?
• The most common cause of bushfires is
lightning strikes.
• Other causes include human causes, ie. people
losing control of camp fires or arson (when
people light fires on purpose)

Why do bushfires spread?
• Winds blow fire and cause them to spread. A change in
wind direction can cause severe bushfires as it causes a
wider spread of fire.
• Bushfires can travel about 10 to 12 km/hr in forests and
20 km/hr or more over grassland.

What controls fire behaviour?
• Fire behaviour is controlled by:
– moisture content
– wind speed
– temperature