Lecture 11 - wildfires

Question 1

most common cause of natural wildfires

Answer 1

lightening and volcanic eruptions

Question 2

what happens after the wildfire?

Answer 2

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​

Question 3

adaptation to wildfires: species

Answer 3

Many species have evolved to either withstand fire or promote the life of the species after a fire event

Question 4

examples of adaptations to wildfires

Answer 4

Redwood and oak trees have bark that resists fire damage​

Some pine trees have cones that only open after a fire​

Question 5

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?

Answer 5

A warmer and or drier climate​

Increased use of fire by humans for clearing land and for heat, cooking, etc.

Question 6

3 elements of wildfires

Answer 6

fuel, oxygen and heat.

If any of these are lost, fire will go out naturally

Question 7

3 phases of wildfire

Answer 7

pre-ignition, combustion, and extinction ​

Question 8

pre-ignition phase

Answer 8

*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

Question 9

combustion phase

Answer 9

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​

Question 10

types of combustion

Answer 10

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​

Question 11

As a wildfire moves across the land, ​

three processes control the transfer of heat

Answer 11

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

Question 12

heat transfer by wildfires

Answer 12

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

Question 13

extinction phase

Answer 13

combustion has ceased

There is no longer sufficient heat or fuel to sustain a fire

Question 14

types of fuel

Answer 14

leaves, woody debris, decaying organic material, grasses, shrubs​

If diseases or storms down large number of trees, the decaying material dries and burns easily.​

​

Question 15

the density of a forest plays a role

Answer 15

​Western North America, dense boreal (evergreen) forests contain abundant fuel supplies

Question 16

topography influencing wildfires

Answer 16

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)

Question 17

weather influencing wildfires

Answer 17

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

Question 18

types of fires

Answer 18

​​surface fires
Crown fires

Question 19

surface fires

Answer 19

travel close to ground and burn shrubs, leaves, twigs, grass (slower)

Question 20

crown fires

Answer 20

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

Question 21

effects of wildfires

Answer 21

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.

Question 22

regions at risk for wildfires

Answer 22

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

Question 23

Yellowstone national park wildfire: The fires became uncontrollable because

Answer 23

many years of fire-suppression policies in the past had allowed fuel amounts in the park to reach dangerous levels.​

Question 24

the Yellowstone wildfire revitalized…

Answer 24

ecosystems

Question 25

More land area in Canada burned in _______ than in any year in history.​

Answer 25

2023

Question 26

the yellowstone wildfire

Answer 26

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​

Question 27

Fort McMurray wildfire

Answer 27

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

Question 28

Fort McMurray wildfire, The prolonged draught occurred in the area during

Answer 28

the prior winter and recorded high temperatures occurred in the preceding days ​

Question 29

Wildfires linkages to Climate Change​

Answer 29

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 ​

Question 30

mountain pine beetle

Answer 30

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.​