Wildfires

What type of hazard is a wildfire

Biological hazard

A wildfire

-An uncontrolled fire fueled by natural vegetation

-Often start in rural wilderness areas, but migrate to rural urban fringes, affecting populations

3 components needed for ignition and combustion

-Fuel (vegetation to burn)

-Oxygen (air)

-Heat (to bring fuel up to ignition temperature)

A material’s flash point

-The temperature at which it will burst into flames

-For wood it’s 300 degrees (at this temp, it releases hydrocarbon gases that mix with oxygen in the air, combust and create a fire)

Wood’s flash point

300 degrees (at this temp, it releases hydrocarbon gases that mix with oxygen in the air, combust and create a fire)

Causes of fires

-Natural

-Human

Natural causes of fire

Lightning

(climate of low rainfall = dry vegetation = captures fire easier)

Human causes of fires

-Discarded cigarettes

-Children playing with matches

-Camp and agricultural fires getting out of hand

-Arson

(fires have increasingly been caused by humans)

Characteristics of fuel

-Fuel is vegetation

-Has to be of sufficient quantity and dry enough to burn

How does climate effect wildfires

-Affects frequency and duration of droughts (vegetation and litter can accumulate and dry out)

-Affects type of vegetation that grows in an area

-Affects rate at which litter can be produced

Fuel

Vegetation

Litter

Leaves

3 types of fires

-Surface

-Ground

-Crown

Surface fires

-Only burn surface litter

-Easiest fires to put out

-Cause least damage to forest

Ground fires

-Underground in deep accumulations of humus, peat and dead vegetation

-Move very slowly

-Difficult to fully put out

Crown fires

-Burn trees up their entire length

-Most intense and dangerous

Fire behaviour

The manner in which fuel ignites, the flame develops and fire spreads

Factors affecting the spread and magnitude of a fire

-Vegetation type (trees, shrubs etc) and density

-Fuel characteristics (amount and thickness)

-Climate (rainfall and temp of an area)

-Recent weather (temp, wind direction, speed, rain)

-Fire behaviour (how it burns)

Conditions favoring intense wildfires - vegetation type

-Thick undergrowth, closely spaced trees allow fire to spread more easily (surface and crown fires)

-Some trees naturally contain alot of oil, and so burn easier

-Vegetation with needles/loose papery bark ignite easier

Conditions favoring intense wildfires - fuel characteristics

-Fine dry material burns most easily

-Large amounts of fuel that form a continuous cover help fire burn for longer and spread more intense

Conditions favoring intense wildfires - climate

-Semi arid with distinct dry seasons are more prone to fires

-Needs to be some rainfall for vegetation to grow in the first place though

-Over periods of time, area lacks precipitation, have low humidity and high temps giving rise to more intense fires as the fuel dries out (harder to stop once ignited)

Conditions favoring intense wildfires - recent weather

-Stronger winds = faster spread of fire

-Wind can transfer embers that can ignite new areas = expanded spread

-Drought conditions = dried out veg = more flammable

Conditions favoring intense wildfires - fire behaviour

-Crown fires are more intense as they burn trees up their entire length

-Surface fires are less intense as they only burn surface litter

-Creeping fires move across ground surface slowly

-Running fires spread rapidly

Distribution of wildfires

-A rural hazard

-Can occur in most environments

-With continued expansion of humans, fires can occur within boundaries of substantial settlements

Example of area where wildfires are a continuing problem

-Log Angeles Basin, California

-Much of the area is covered by drought resistant chaparral (area too dry for much tree growth)

-Santa Ana dry wind increases vegetation dryness massively and increases fire spread

Primary impacts of wildfires

Physical: fires, air pollution

Human: death, building and vegetation destruction

Secondary impacts of wildfires

Physical: flooding

Human: health issues, homelessness, loss of crops and tourism

Social effects of fires

-People may be killed or injured if they don’t evacuate in time

-Homes are burnt and destroyed so people become homeless

-Power lines can be burnt, leaving people without electricity

-Health problems (inhaling smoke)

Environmental effects of fires

-Release of toxic gases = air pollution

-Plants and wildlife are killed

-Habitats burnt and destroyed

-Soil are damaged due to removal of organic matter

Economic effects of fires

-Businesses are destroyed = loss of jobs and income

-Insurance increases after fire

-Cost of fighting the fire is huge

-Tourist numbers may decline after

Political effects of fires

-Governments can face criticism for their management if the fire has severe impacts

-Governments may have to change their forest management practices

Physical factors effecting level of impact of fires

-Vegetation type and density

-Fuel characteristics

-Climate (rain, humidity, temp)

-Recent weather

-Type of fire (surface, ground, crown)

-Magnitude of fire

-Wind speed and direction

-Number of fires

Humans factors effecting level of impact of fires

-Level of development

-Level of preparedness

-Population density

-Type of infrastructure

-Human response

-Proximity of urban areas to rural areas

Can wildfires be prevented

Yes

How can wildfires be prevented

-Education (on risk factors and how to avoid starting them)

-Fire breaks (remove fuel from a section of land)

-Controlled burning (dry litter on ground is burnt and removed to reduce fuel available for surface fires)

Fire breaks

Removing a line of vegetation to stop a fire spreading

Controlled burning

Dry litter on the ground is purposefully burnt and removed to reduce fuel available for surface fires

Mitigation of fire risks

-Managing vegetation (controlled burning and fire breaks in advance)

-Managing built environment (increase the gap between houses and vegetation)

-Hazard mapping (identify areas at higher risk of fires and prevent building there)

-Fire breaks

-Controlled burning

-Fire resistant materials (using stone and brick rather than wood in buildings)

-Education (on risk factors and how to avoid starting fires)

Adaptation to fire risks

-GIS modelling (used to study ways fire behaves to predict fires behaviour)

-Insurance (expensive in fire prone areas)

-Warning systems (establish lookout towers/air patrols)

-Emergency plans and kits in households

-Shelter (created in emergency)

-Supplies of retardants (slow the spread of fires)

-Evacuations

Park model for fires

-Stage 1: create fire breaks, building using fire resistant materials, controlled burning, hazard mapping

-Stage 2: put out fire with firefighters and retardants, evacuation, firebreaks to limit spread

-Stage 3: search and rescue for survivors, treat injured

-Stage 4: emergency aid provided, temporary structure built

-Stage 5: long term aid, permanant infrastructure

Hazard management cycle for fires

-Prevention/mitigation: create fire breaks, carry out controlled burning, use fire resistant materials for building, hazard mapping

-Preparation: educate people, train emergency services, put warning systems in place, create emergency plan

-Response: order evacuations, put out fire with firefighters and retardants, fire breaks, controlled burning, treat injured, search and rescue for survivors

-Recovery: infrastructure rebuilt, long term aid given, replant vegetation stripped from fire