3.1.5.6 Fires in nature

Nature of wildfires. Conditions favouring intense wild fires: vegetation type, fuel characteristics, climate and recent weather and fire behaviour. Causes of fires: natural and human agency.

What is a wildfire?

Wildfire: A large, uncontrolled fire that quickly spreads through vegetation.

Outline the formation of wildfires [4 marks]

Outline the conditions favouring intense wildfires [4 marks]

list them

Vegetation Type: Thick, close together vegetation allows fires to spread quickly and easily. Trees and thick bushes lead to more intense wildfires; grasslands do not burn as intensely. Vegetation with flammable oils - like eucalyptus - causes more intense fires also.

Fuel Characteristics: Vegetation should be dry to allow it to catch. Finer vegetation causes fires to spread quicker, but larger, thicker forms of vegetation burns for longer and more intensely

Climate and recent weather:

Wildfires occur in a climate that has enough rainfall to have sufficient plant growth , but considerable dry spells and droughts to dry out the fuel. An example of this is California.

California El Niño is thought to provide warmer, wetter seasons to grow vegetation, and La Niña’s dryer seasons create more wildfires.

Recent temperature increases have caused an increase in the number of wildfires and an increase the length of wildfire seasons.

Argument that climate change is causing more wildfires: “Forest fires in the western US have been occurring nearly 5x more often since the 1970s and 80s. Such fires are burning more than 6x the land area as before, and lasting almost 5x longer.”

Argument that climate change is not causing more wildfires:

There are also arguments that despite climate change, wildfires are not increasing everywhere. Studies have shown that this is somewhat true; between 1998 and 2015 globally burned area declined about 24 percent. However, this may also be down to agricultural productivity and land use change as there are less areas that can be burned, i.e. less forestry

(Fire behaviour refers to how they spread)

Wildfire does not just spread in one way; there are three main types of wildfire burning.

● Crown fires burn the entire tree from bottom to top , which is classed as the most dangerous and destructive type of fire. ● Surface fires only burn the leaf litter, meaning they are easy to extinguish.

● Ground fires burn at the dry peat or vegetation beneath the surface , and move slowly through the dried underground. Due to them being underground, they can be difficult to put out and can actually continue to burn throughout the year if the weather conditions allow it.

Outline how vegetation type favours intense wildfires [4 marks]

Vegetation Type: Thick, close together vegetation allows fires to spread quickly and easily. Trees and thick bushes lead to more intense wildfires; grasslands do not burn as intensely. Vegetation with flammable oils - like eucalyptus - causes more intense fires also.

Outline how fuel characteristics favours intense wildfires [4 marks]

Fuel Characteristics: Vegetation should be dry to allow it to catch. Finer vegetation causes fires to spread quicker, but larger, thicker forms of vegetation burns for longer and more intensely

Outline how climate and recent weather favours intense wildfires [4 marks]

Wildfires occur in climates that have enough rainfall to have sufficient plant growth, but considerable dry spells and droughts to dry out the fuel. An example of this is California.

California El Niño is thought to provide warmer, wetter seasons to grow vegetation, and La Niña’s dryer seasons create more wildfires.

Recent temperature increases have caused an increase in the number of wildfires and an increase the length of wildfire seasons.

Argument that climate change is causing more wildfires: “Forest fires in the western US have been occurring nearly 5x more often since the 1970s and 80s. Such fires are burning more than 6x the land area as before, and lasting almost 5x longer.”

Argument that climate change is not causing more wildfires:

There are also arguments that despite climate change, wildfires are not increasing everywhere. Studies have shown that this is somewhat true; between 1998 and 2015 globally burned area declined about 24 percent. However, this may also be down to agricultural productivity and land use change as there are less areas that can be burned, i.e. less forestry

Outline how fire behaviour favours intense wildfires [4 marks]

(Fire behaviour refers to how they spread)

Wildfire does not just spread in one way; there are three main types of wildfire burning.

● Crown fires burn the entire tree from bottom to top , which is classed as the most dangerous and destructive type of fire. ● Surface fires only burn the leaf litter, meaning they are easy to extinguish.

● Ground fires burn at the dry peat or vegetation beneath the surface , and move slowly through the dried underground. Due to them being underground, they can be difficult to put out and can actually continue to burn throughout the year if the weather conditions allow it.

Outline causes of wildfires [4 marks]

Causes of wildfires

There are natural and human causes of wildfires but 90% of wildfires are caused by humans.

Natural causes

• Lightning is the biggest natural cause of wildfires.

• Spontaneous heating is where leaves and branches on the ground are heated to the point at which it catches fire without a spark.

Human causes

• Arson where fires are started deliberately

• BBQ's and campfires that have not been extinguished properly

• Discarded cigarettes