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