wildfires

what are wildfires?

* self-sustaining fires that start and spread out of control; often move into populated or agricultural areas

what are the diff causes of fires?

• number 1 natural cause → lightning

• arson

• campfires, smoking, playing

• transport

• elec power

• machinery

• debris burning

• unknown

• other anthropogenic causes

• 90% forest firest in US caused by human activity

what is at risk with fires?

• humans

• ecosystem

fires in Canada

• numb of fires each yr in Canada n total burned

• there is no correlation between the total area and the num of fires, as a few individual large fires account for most of the area

• there r many small fires

• less big ones

what is fire?

* when gases react w/ oxygen to produce heat and light

what are flames?

* superheated gases (carbon dioxide, carbon monoxide, nitrogen, oxygen, water vapour and organic chemicals)

what produces gases which fuel the fore?

* breakdown of cellulose, fats, oils and sugar in plant walls and cells produces gases which fuel the fire

what burns at relatively low temp?

* cellulose and hemicellulose

when does lignin burn?

• burn at higher temperature than cellulose

• tree species high in lignin (e.g., oak) will not burn as readily

when does extractable burn?

• flame suddenly when exposed to heat

• contribute to the violence of wildfire in many conifer forest

• ex. resins, fats, oils

• unpredictable

what is necessary to keep fire burning?

• oxygen

• heat

• fuel

• known as the fire triangle

what is the preheating stage?

* heat source raises a fuel’s temperature; water evaporates

what is the pyrolysis stage?

* molecs in fuel decompose to produce gases that rise in the air

what is the combustion stage?

* gases ignite and react with oxygen → produce fire

what is flaming combustion?

• dominates early fire

• produces large flames and little smoke

• initiated by ignition of volatile gases at 260ºC -450ºC

• temperatures can rise to 1,500ºC; high enough to melt metal and glass

what is smoldering combustion?

• produces the most smoke

• lack flames - associated w/ conditions where oxygen is lim

combustion

where do ground fires occur?

• within roots and buried organic matter

• creep along under ground surface

• little flaming, more smoldering; limited oxygen

where do surface fires occur?

• burn low-lying vegetation (undergrowth and forest litter ex. grasses and dead leaves)

• burn slowly with smoldering, limited flaming

what do ladder fires burn?

* undergrowth and medium-sized trees (below the forest crown)

crown fires?

• flaming is carried via tree canopies

• driven by strong winds and steep slopes

• can jump from crown to crown without burning undergrowth

what is fire severity?

* percent biomass that burns during a fire

what is fire intensity?

* measure of energy released during burning

what is flame length?

• distance from the base to the end of the flame

• more intense fire = longer flame length

what is conduction?

* transfer of heart directly from molec to molec

what is convection?

• transfer of heat by the movement of heated air

• hot gases are less dense and rise; pulls in fresh air to sustain combustion

what is radiation?

* radiant energy heats fuel within 10-35m of a wildfire

what are firebrands?

* sparks and embers can land on fresh fuel beyond the wildlife; start new fires

how do wildfires spread?

• start most often when a small heat source (spark from campfire, cigarette) comes into contact with dry grasses, leaves, small sticks

• heat from this small fire pre-heats surrounding fuel

what does spread depend on?

• fuel

• weather (wind)

• terrain

what do sparse or wet fuels result in?

• less intense wildfires

• seasonal changes dictate moisture lvls in fuel

what does wind replace during burning?

• oxygen consumption

• also tilts flames causing preheating and spreading firebrands

what do flaming gases and hot rise via?

• convection

• allows for fires migrate faster up slopes than down slopes

what are ways enviro has adapted to fire?

• trees like cork oak have adapted to fire

  • their sponge bark does not burn

• Jack pine are well adapted to fire, as the heat of the fire opens their cones liberating the seeds

what are primary disaster of wildfires?

• injury and death

• property, agricultural, and forest losses

what are secondary disaster of wildfires?

• health effects from smoke inhalation

• increased soil erosion

• destabilizes slopes - can lead to landslides

• longer impact

Australia Bushfires 2020

• known as the “black summer”

• 5,900 buildings destroyed

• 34 deaths

• affected ~3 billion animals

• some endangered species believed to have been driven to extinction

• air quality hazardous in all southern and eastern states of Australia

• estimated to cost upwards of $100B

• Australia costliest natural disaster to date

• biggest concern was wildlife

  • millions animals killed

• no ele, water, phone service in some areas

• not much govern help

• strong winds

fire suppression methods

• firebreak construction

• plane dropping retardant

• create break + start new fire

forest management

• total fire suppression (1940’s-1980s) results in large fuel accumulations and larger fires

• increased knowledge in forest ecology demonstrated the importance of fire for forest renewal

• policy has shifted toward prescribed burns in some areas to reduce large fuel accumulations

• natural lightning-caused fires were allowed to burn unless they posed threats to people, commercial timber lands or scenic attractions

there is a growing num of ____________ ______________________ bringing humans closer to fire risk

* interface communities

how to reduce risk?

• homes should be constructed from flame resistant material

• area around homes should be clear of brush

• a clear emergency plan and response should be in place