Understanding bushfire behaviour

What starts bushfires, and what conditions influence the spread of bushfires?

Focus statement

A jigsaw strategy is used to organise students into expert groups to enable them to collaboratively discover ways in which bushfires start, and the ways in which bushfire spread is influenced by factors of climate, weather, topography and fuel. The Fire Danger Rating scale incorporates factors that influence bushfires.

Key message

The conditions that influence bushfire behaviour are major determinants of the Fire Danger Rating. The Fire Danger Rating is your trigger to act, so to stay safe you need to be aware of the Fire Danger Rating in your district.

Activity

Establish home teams of five students. A student from each team will become an 'expert' in one of the factors to be explored. Number off the students in each team, from one to five. This number will be their expert group.

Send students off to their expert groups. Ensure all necessary resources are available for them to use. As an expert group, students need to clarify their task and use the available resources to understand more about the factor they have been assigned, and how it relates to bushfires.

Each student expert takes their own record of the group's work and collaboratively developed ideas back to their team. Experts then combine their ideas in their team in a synthesis activity. Distribute copies of the task sheets to each expert group.

Note: For safety, the teacher will need to supervise expert group 5 while they carry out their scientific demonstration. At other times, the teacher roams between the groups to guide and support students as required.

Expert group 1: Ignition of bushfires

Students study the statistics of the causes of bushfire ignition (task sheet 1). The expert group considers the question: Where and how are bushfires started?

Students research the issue using links to websites as Department of Sustainability and Environment Victoria, CSIRO, Geoscience Australia and Emergency Management Australia.

The expert group identifies the main causes of bushfire ignition, ranks the causes of bushfires from those causing the most number of bushfires to causing the least number of bushfires, and nominates which of these causes are most preventable.

Expert group 2: Climate and seasons

In the task sheet 2, students are reminded that 'climate' refers to the average, or typical, weather conditions observed over a long period of time for a given area. It is determined by factors such as latitude (amount of incoming solar radiation), altitude above sea level and proximity to oceans.

The expert group considers the question: Where and when do bushfires occur?

Students view Sentinel, the national bushfire monitoring system, which indicates where fires are currently burning in Australia. Once they have selected their internet connection and read the disclaimer, students can select a particular state from the Find tab and review the current fires in that state. Students should note where bushfires are occurring today. Did they expect this? Had they heard about these bushfires? They should also note wind and relative humidity data if shown.

Students also view the Geoscience Australia and the CSIRO websites for information about bushfire seasons across Australia.

Students are asked to describe the distribution of bushfires in Australia and name the highest risk areas, based on what they know about the vegetation and population distribution of Australia.

Students use the task sheet with graphs of Melbourne area to interpret and make connections between climate and bushfires.

Alternatively students could locate, analyse and interpret their own annual rainfall and minimum and maximum temperature data. They can use the Bureau of Meteorology, Climate Data Online resource. Students can create their own graphs selecting an area of interest, for example Melbourne, and select a weather station.

Students relate their ideas to what they know about the bushfire season. As a group, they develop an explanation about the way in which climate influences bushfires. They discuss extended drought and its relationship to the threat of bushfires.

For years 9-10: Provide internet access for students to review the climate resources below, all from the Bureau of Meteorology. Discuss the effects maximum temperature, rainfall, relative humidity and broader climate influences such El Niño and La Niña events.

Expert group 3: Weather

Using the task sheet 3 to guide their discussion, students identify and discuss common weather elements that contribute to increased fire danger. These elements include high temperatures, low humidity and high winds following a period of dry weather. Students make the connection between these conditions and the dryness of fuels, which will need less preheating in order to burn.

Provide printed copies of the two articles below for students to read (both from Bureau of Meteorology). Students will use this information to update the table, provided as part of their task sheet, which describes common elements of weather that contribute to increased fire danger.

Students use the images provided in the task sheet to establish the way in which embers are blown by the wind ahead of the fire front, and cause spot fires. Explore the effect of wind changes using relevant images provided on the student task sheet.

Expert group 4: Topography

Provide students with the task sheet 4, that includes images of different terrain and obstacles that a bushfire may travel over. The images include hills, valleys, flat grasslands, waterways and country road. Students discuss their predictions of how each of these would affect the movement of a bushfire.

Students describe the effect of slope on a fire's movement. Guide students to establish that the speed of the fire increases as it moves uphill and decreases downhill. Relate this to the unburnt fuel.

Expert group 5: Fuel (requires a teacher demonstration)

Using the task sheet 5, students refer to images of different vegetation that clearly show the fuel types in a natural area, for example: Fuel to burn: leaves, bark and bush litter, long dry grasses, fallen logs, tall trees and the understory plants. Also include images of the built environment for fuel such as houses and their surrounds.

Teacher demonstration: Have students observe two leaves of the same kind: one that is dry, and one that has recently been removed from a tree. Students describe their observations. Demonstrate how combustible each leaf is, using safety procedures and having water available to extinguish the leaf. If possible, take digital photographs or video and provide these resources for students to describe and present their ideas. Relate the dryness of materials such as fallen leaves and branches in a forest area, and the grasslands that dry out as a result of continued high temperatures and winds. Use the term moisture to describe how much water a leaf holds.

Students observe the range of branches and leaves that could be expected to fall on a forest floor. Prompt students to think about the size of the materials and how this may influence the bushfire starting and spreading. Discuss how the material may be arranged, relate to the air flow (access to oxygen). Introduce the term compactness to describe the way the fuel is arranged.

Return to home team (synthesis activity)

Students return to their home teams and share their ideas, which they developed as part of their expert groups, about what causes bushfires and what influences bushfires.

For years 7-8 students: Provide each team with the Fire Danger Rating information brochure. As part of a class discussion, students use this information and the ideas developed in the expert groups to describe how the factors that influence bushfire behaviour relate the Fire Danger Rating.

Students create a mock weather report for a 'special edition' bushfire report. Students relate the conditions that have changed over a week to the Fire Danger Rating. Students are encouraged to bring together elements of their expert groups in this 'special edition' bushfire report.

For years 9-10: Ask each team to create a blog that features the thread: 'Be aware that high temperatures cause bushfires. It's coming up to January, so watch out for those hot days and the threat of bushfires. Read my tips about bushfires and how to stay safe.'

Ask each team to base their response on the evidence they have collected. Teams should include any images they believe are relevant to their response.

Conclude the session by viewing the team blogs and comparing each team's response. Do students correctly explain that the thunderstorms, wind, humidity and high temperatures contribute to increased bushfire danger?

Vocabulary

climate, compactness, dryness, embers, Fire Danger Rating, fuel, ignition, relative humidity, moisture, spot fires, understory, vegetation, wind direction, wind strength