Presentation on theme: "BUSHFIRES IN AUSTRALIA"— Presentation transcript:
BUSHFIRES IN AUSTRALIA http://www.youtube.com/watch?v=ALSNRq1eGJU
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 OxygenFuel
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. 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. 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. 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. http://www.youtube.com/ watch?v=MG9y5-a9M_M http://www.youtube.com/ watch?v=MG9y5-a9M_M
What controls fire behaviour? Fire behaviour is controlled by: moisture content wind speed temperature