Lecture 20 - Forest Fires Flashcards
When are the earliest records of fire from?
quickly after land plants evolved ∼450 Ma
What ecosystem processes and patterns does fire influence?
vegetation distribution and structure
the carbon cycle
climate
etc
What happens during a fire in terms of atoms?
During a fire, carbon-hydrogen (C-H) bonds in plant material are broken, generating carbon dioxide (CO₂), water vapour (H₂O), and heat:
C₆H₁₂O₆ (glucose) + 6O₂ → 6CO₂ + 6H₂O + energy (heat).
What does the fire triangle describe?
It describes the three elements required for a forest fire to burn: heat, oxygen, and fuel.
What is the first stage of combustion?
ignition
How can ignition be triggered?
naturally - lightning
by humans - discarded cigarettes, campfires, power-line arcs and sparks from equipment or vehicles
What type of fire is responsible for the great majority of the total area burned in all forest fires? Why?
Natural fires, because they often burn for hours before being detected.
What type of fire is responsible for the greater percentage of forest fires?
Human-caused fires
Why are human-caused fires normally better contained?
they are usually detected early
What is the second stage of combustion?
preheating, in which the ground heats up and water is expelled from plants
What is the third stage of combustion?
flaming combustion
What stage of combustion releases the greatest energy in the fire?
flaming combustion - third stage
What is the final stage of combustion?
glowing or smouldering - this involves slower combustion rates and emits smoke but no flames and is rarely self-sustained
Apart from ignition, how else can forest fires be classified?
the part of forest they burn in
Where do ground fires occur?
on the ground (often below the leaves)
Where do surface fires occur?
on the forest surface (up to ∼1 m high)
Where do crown fires occur?
in the tops of trees
Can different types of fire occur simultaneously?
yes - it is not uncommon for two or three types of fires to occur simultaneously
What are some examples of ladder fuels?
tall grasses
small shrubs
What does the presence of ladder fuels enable fires to do?
They enable small ground fires to carry upward into tall trees and create major wildfires engulfing the tree crowns.
What is the main factor in determining the likelihood of wildfires starting and their rate of spreading?
climate and weather conditions
What climate and weather conditions are responsible for escalating fires?
high temperatures high wind speeds the occurrence of lightning low humidity low soil moisture low rainfall
What are the other factors in determining the likelihood of wildfires starting and their rate of spreading?
Type and state of vegetation - plant species with high oil content are easiest to ignite, and plant matter weakened or killed through drought, disease, or infestation (e.g. “beetle kill”) is highly combustible.
Topography - wildfires spread quickest upslope where vegetation is preferentially preheated.
When is the fire triangle broken?
when not enough heat is generated to sustain the process
when the oxygen supply is limited
when the fuel is exhausted, removed, or isolated
How does fire suppression work?
removing one or more of the elements of the fire triangle
What are some examples of fire suppression methods?
adding water to remove heat
adding fire retardants to block oxygen (typically a chemical that coats the plant, to limit its oxygen contact)
removing the fuel by bulldozing
by starting backfires
When are fires easiest to suppress?
when they are still small
How can fires be detected?
fire lookouts
remote sensing technology
Why can the suppression over decades of wildfires be dangerous?
This can result in a dangerous buildup of fuel that can make subsequent fires much worse. This is a significant factor in many of the recent record-breaking wildfires in western North America.
How many hectares did the 1919 great fire (Alberta, Canada) burn?
2,000,000 hectares
How many people needed to be evacuated from the city of Fort McMurray in 2016?
∼60,000 people
When did the 2016 Fort McMurray fire ignite?
1st May 2016
Where did the 2016 Fort McMurray fire ignite?
15 km from Fort McMurray
Why did the 2016 Fort McMurray fire ignite?
likely due to humans
On what day did the 2016 Fort McMurray fire engulf the whole city?
4th May
When was the 2016 Fort McMurray fire brought under control?
5th July
How much land did the 2016 Fort McMurray fire burn?
600,000 hectares (6,000 km²)
How many buildings were destroyed by the 2016 Fort McMurray fire?
> 2,400 buildings
What were the estimated losses due to the 2016 Fort McMurray fire?
∼$10 billion (insured and uninsured) - this is Canada’s costliest disaster
What were the main causes of the 2016 Fort McMurray fire?
increasing temperatures
longer spells of dryer weather (due to anthropogenic climate change)
What percentage of the world’s forests are in Canada?
about 10%
Where in Canada is fire common?
forests
shrub lands
grasslands
How much of Canada’s surface area is covered by boreal forest?
60%
What types of trees make up boreal forests?
mixed coniferous and deciduous trees
What is a hectare?
10,000 m²
How do fires create their own weather?
The burning vegetation creates a moist air mass that rises and condenses into pyrocumulus clouds. These can produce rain, helping extinguish the fire, or create lightning, igniting new fires.
The rising air leaves behind low pressure at the surface, drawing in air as downdrafts. These can produce dangerous shifts in the intensity and direction of the fire. Rising columns of hot, unstable air can be spun into dangerous eddies called fire whirls. They are normally <50 m tall, though ones fire whirls taller than 1 km have been observed.
How many people died as a result of the 2018 Camp Fire?
88 people
How many buildings were destroyed as a result of the 2018 Camp Fire?
over 10,000 buildings
What was the deadliest and most destructive wildfire in California history?
the 2018 Camp Fire
When did the 2018 Camp Fire start?
November 8, 2018
Where did the 2018 Camp Fire start?
in Northern California’s Butte County
What ignited the 2018 Camp Fire?
a faulty electric transmission line
When was the 2018 Camp Firefully contained?
November 25 - due to the first winter rainstorm of the season
How much area did the 2018 Camp Fire cover?
153,336 acres (62,053 ha)
What was the total cost of the damage caused by the 2018 Camp Fire?
$16.5 billion
What weather condition was a factor in the 2018 Camp Fire?
Drought - possibly intensified by climate change
