Week 11 Flashcards
what are the most common causes of natural wildfires?
lightning
volcanic eruptions
what happens after wildfire?
after a fire, vegetation completes a cycle from early colonizing plants to mature ecosystems
the new ecosystem that evolves adapts to the climate of that location and time
how have species adapted to wildfires? give examples
many species have evolved to either withstand fire or promote the life of the species after a fire event
e.g.
redwood and oak trees have bark that resists fire damage
some pine trees have cones that only open after a fire
geologic records shows an increase in the amount of charcoal in sediment dated to approximately 10,000 years ago – suggesting 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.
what 3 elements are required for a wildfire?
fuel, oxygen, and heat… if any of these are lost, the fire will dissipate
plants absorb CO2 and store carbon in their tissues
during a wildfire, this CO2 is released back into the atmosphere
what are the 3 phases to a wildfire?
pre-ignition
combustion
extinction
describe the pre-ignition phase of a wildfire
during this phase, vegetation reaches a temperature at which it can ignite
as vegetation is heated, it loses water
heat radiating from the flames of a wildfire can preheat nearby vegetation
describe the combustion phase of a wildfire
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
what is flaming combustion?
a type of combustion that is a rapid, high-temperature conversion of fuel into heat
it is characterized by large flames and a high amount of unburned material
what is smouldering combustion?
occurs in areas with ash and already burned material
what type of combustions are there?
flaming combustion
smouldering combustion
what 3 processes control the transfer of heat as a wildfire moves across the land? describe them
conduction
—- transfer of heat by solid to solid contact
radiation
—- transfer of heat in the form of invisible waves
convection
—- transfer of heat by movement of a liquid or a gas
in wildfires, heat transfer is mainly be 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
describe the extinction phase
in this phase, combustion has ceased
there is no longer sufficient heat or fuel to sustain a fire
give some examples of types of fuel
includes leaves, woody debris, decaying organic material, grasses, shrubs, etc.
how can fuel play a role in wildfires?
if diseases or storms down many trees, the decaying material dries and burns easily
the density of the forest plays a role: in western North America, dense boreal forests contain abundant fuel supplies
how can topography play a role in wildfires?
the risk of fire can vary by slope orientation
in the Northern Hemisphere, south-facing slopes are relatively warm and dry
slopes exposed to prevailing winds are often drier
wildfires burning on steep slopes preheat fuel upslope from the flames
—— this results in the rapid spreading of a fire upslope
how does the weather affect 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 and wind can carry embers that can ignite spot fires ahead of a main front
what are the 2 types of wildfires? describe them
surface
—- these fires travel close to the ground and burn shrubs, leaves, twigs, grass, etc.
—- they vary in intensity but most move relatively slow
crown
—- they move rapidly thru the forest canopy by flaming combustion
—- they can be fed by surface fires that move up limps or tree trunks or they may spread independently of surface fires
—- they are driven by strong winds and are common in boreal forests
what are the effects of wildfires on soil?
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
this repels water, it increases runoff and erosion
it may persist for several years following a fire
describe the effects of wildfire in regards to air quality
an increase of airborne particles and haze can be observed thousands of km downwind of large fire
in Canada, what regions are at risk of wildfires?
BC and the boreal forests of the Canadian Shield region
the geographic region most at risk changes annually with the weather and corresponds to areas that are experiencing droughts
describe the Yellowstone National Park Wildfire
a series of lightning strikes caused 50 fires in the park in 1989
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 in nearly 10,000 firefighters
the fires were beyond the control of the crews and burned for several months
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 fires of 1988 revitalized ecosystems in the park
officials remain committed to the natural-burn policy today this is common policy in national parks
in what year did more land area in Canada burn than any other year?
2023
describe the 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
the cause of the fire has not been determined
but a prolonged drought occurred in the area during the prior winter and record high temperatures occurred in the preceding days
