Y13 MB - Wildfires Flashcards
What is a wildfire?
An uncontrolled rural fire
What are wildfires known as in Australia and North America?
Bushfires
What are the three main types of wildfire?
Ground fire
Surface fire
Crown fire
What is a ground fire?
A slow smouldering fire that burns organic matter in the soil (such as peat)
They spread slowly and at fairly low temperatures for long periods of time
There may be no flame
What is a surface fire?
The burning of leaf litter and low lying vegetation
The most common type of fire
Can be low or high intensity
Cool quickly and are relatively easy to control
What is a crown fire?
Fire that moves rapidly through the canopy (top layer of vegetation)
Hottest type of fire
Very difficult to contain
What is the hottest kind of fire?
Crown fire
What is the most common kind of wildfire?
Surface fire
What is the process by which fire may spread from the ground to the tree canopy?
The ‘ladder effect’
What is the ‘ladder effect’
Where fire spreads from the ground to the tree canopy by igniting low branches and shrubs
What is needed for a wildfire to occur?
Ready supply of fuel (dry vegetation)
Ignition source (natural or human)
Favourable climatic or weather conditions
Where is the only continent a wildfire can’t take place?
Antarctica
Describe what conditions cause wildfires to travel faster
Wildfires travel faster uphill than downhill
The steeper the slope the faster they travel
Give an example of a low heat output and high heat output area for wildfires
Grassland - low heat output
Forested area - high heat output
What is the impact of eucalyptus and pine trees on wildfires?
They contain lots of oil so burn easily
What are firebrands and in what conditions do they occur?
Firebrands are when eucalyptus trees shed long strings of bark which then encourage the rate of the wildfire spreading
What conditions are optimum for the spread of a wildfire?
Rainfall sufficient for the growth of vegetation (fuel source)
Distinct dry season (when vegetation dries up it becomes more flammable)
Strong winds (provide oxygen and help the fire spread)
Cyclical climatic events such as El Niño
What is the El Niño cyclical climatic event?
Westerly trade winds weaken so less warm water is transferred to the west which reduces the pressure difference between the east and the west
The temperature of the eastern Pacific Ocean rises causing warmer temperatures in South America
There is therefore more precipitation in South America so drier conditions in Southeast Asia and eastern Australia increasing the risk of wildfires there
What are the natural ignition sources of wildfires?
Lightning
Volcanic eruptions
Burning fragments (firebrands) being blown ahead of flames and igniting new areas of forests - spot fires
Heat transfer processes heat vegetation further ahead of the flames causing the fire to spread more quickly
How are spot fires caused?
Firebrands being blown forwards and igniting new areas of forest ahead of the wildfire front
Firebrands rolling down steep slopes and creating spot fires there
Why are wildfires so good at climbing uphill?
Heat transfer processes (e.g conduction and convection) heat vegetation ahead of the flames causing fires to spread more rapidly
Hot air rises so heat is transferred vertically
What are the human ignition sources of wildfires?
Discarded cigarettes
Poorly controlled campfires
Arson
What are the areas called where woodland particularly close to urban areas is vulnerable to wildfires caused by humans?
Wildland-urban interfaces
How may wildfires have positive impacts?
They remove dead or dying material from the forest floor as well as harmful insects and diseased plants —> encourages new plant growth
Some species of plant cannot reproduce without fire e.g the Douglas fir need fire to aid seed germination
Give some mitigation strategies for wildfires
Satellites with infrared sensors to detect thermal variation
Back burning where controlled fires are lit to burn the fuel (vegetation) ahead of a wildfire
What are firebreaks and is this an example of mitigation, adaptation, prevention or preparedness?
Where areas of vegetation are burned in forested areas to halt fires from spreading
Adaptation strategy
What percentage of wildfires are due to humans?
85%
