Lecture 11 - wildfires Flashcards
most common cause of natural wildfires
lightening and volcanic eruptions
what happens after the wildfire?
vegetation completes a cycle from early colonizing plants to mature ecosystem.
The new ecosystem that evolves adapts to the climate of that location and time
adaptation to wildfires: species
Many species have evolved to either withstand fire or promote the life of the species after a fire event
examples of adaptations to wildfires
Redwood and oak trees have bark that resists fire damage
Some pine trees have cones that only open after a fire
The geologic record shows an increase in the amount of charcoal in sediment dated to approximately 10,000 years ago.
This suggests a high amount of wildfire activity at the time. Why might this be?
A warmer and or drier climate
Increased use of fire by humans for clearing land and for heat, cooking, etc.
3 elements of wildfires
fuel, oxygen and heat.
If any of these are lost, fire will go out naturally
3 phases of wildfire
pre-ignition, combustion, and extinction
pre-ignition phase
*pre heating phase
vegetation reaches a temperature at which it can ignite.
As vegetation is heated, it loses water
Heating radiating from the flames of a wildfire can pre heat nearby vegetation
combustion phase
Pre-heating results in fuel that is prone to ignite.
The combustion phase begins with ignition that could be from a natural (lightning) or human cause.
Not all ignitions will result in a wildfire; the vegetation must already be dry from pre heating
types of combustion
Flaming combustion is the rapid, high temperature conversion of fuel into heat.
It is characterized by large flames and a high amount of unburned material.
Smouldering combustion occurs in areas with ash and already burned material
As a wildfire moves across the land,
three processes control the transfer of heat
Conduction: Transfer heat by solid-to-solid contact
Radiation: Transfer heat in the form of invisible waves
Convection: Transfer of heat by movement of a liquid or a gas
heat transfer by wildfires
In wildfires, heat transfer is mainly by radiation and convection.
Heat from radiation increases the surface temperature of the fuel.
As air is heated, it becomes less dense and rises
The rising air removes heat from the zone of flaming, and it is replaced by fresh air.
This fresh air (oxygen) sustains the combustion
extinction phase
combustion has ceased
There is no longer sufficient heat or fuel to sustain a fire
types of fuel
leaves, woody debris, decaying organic material, grasses, shrubs
If diseases or storms down large number of trees, the decaying material dries and burns easily.
the density of a forest plays a role
Western North America, dense boreal (evergreen) forests contain abundant fuel supplies
topography influencing wildfires
The risk of fire can vary by slope orientation.
In the Northern Hemisphere, south facing slopes (riskier) are relatively warm and dry
Slopes exposed to prevailing winds are often drier
Wildfires burning on steep slopes preheat fuel upslope from the flames (moves faster upslope then downslope)
weather influencing wildfires
Large wildfires are most common following a drought.
In a dry thunderstorm, the rain evaporates before reaching the ground. Lightning from these storms is more likely to produce a wildfire.
Wind can enhance preheating of fuel
Wind carries embers that can ignite spot fires ahead of the main fire front
types of fires
surface fires
Crown fires
surface fires
travel close to ground and burn shrubs, leaves, twigs, grass (slower)
crown fires
move rapidly through the forest canopy by flaming combustion.
Fed by surface fires that move up limbs or tree trunks or may spread independently of surface fires
They are driven by strong winds and are common in boreal forests.
Intermittent crown fires consume the tops of some trees in an area.
Continuous crown fires consume the tops of all trees
effects of wildfires
Fires that burn soil may leave behind a hydrophobic layer at the surface.
This layer is caused by the accumulation of chemicals from burned vegetation.
Since layer repels water, increase surface runoff and erosion
It may persist for several years following a fire
An increase of airborne particles and haze can be observed thousands of km downwind of large fires.
regions at risk for wildfires
In Canada, the wildfire risk is greatest in British Columbia and in the boreal forests of the Canadian Shield region.
The geographic regions most at risk changes annually with weather and corresponds to areas that are experiencing draught
Yellowstone national park wildfire: The fires became uncontrollable because
many years of fire-suppression policies in the past had allowed fuel amounts in the park to reach dangerous levels.
the Yellowstone wildfire revitalized…
ecosystems
More land area in Canada burned in _______ than in any year in history.
2023
the yellowstone wildfire
A series of lightning strikes caused 50 fires in the park in 1988.
Park officials have a policy that allows naturally caused fires to burn without intervention
This became controversial as hot, dry weather that summer allowed the fires to spread and merge.
Officials responded to political pressure and eventually called
Fort McMurray wildfire
The wildfire in 2016 caused $10B in damage making it the costliest disaster in Canadian history.
There were no deaths or injuries due to the evacuation of the entire city in advance
Residents were displaced for four weeks and over 2000 people lost their homes in the wildfire.
cause = not determined
Fort McMurray wildfire, The prolonged draught occurred in the area during
the prior winter and recorded high temperatures occurred in the preceding days
Wildfires linkages to Climate Change
Climate change increases the likelihood and the intensity of wildfires.
Climate change affects both temperature and precipitation and can lead to severe droughts.
In some parts of the world, grasslands will replace forests. Current areas of forest will expand poleward.
Insect infestations can cause disease throughout a forest making it more vulnerable to wildfire
mountain pine beetle
The beetle has destroyed 80% of mature Mountain pine forests in British Columbia.
The economic consequences will be felt for decades in the BC interior
The beetle is also posing a threat to Jackpine forests in Alberta.
With warmer seasonal temperatures, the beetle has evolved to survive through the winter in B.C.
