Understanding the background to wildfire hazards Flashcards
What does a fire require to start?
Fuel, Heat, Oxygen
What is a growth fire?
Burning below the surface of the ground
What is a surface fire?
Fire that burns loose debris on the surface, which includes dead branches, leaves, and low vegetation.
What is a crown fire?
A fire that spreads from tree top to tree top
What conditions favour wildfires?
Dry Hot Windy Low humidity Fuels - certain plants are pyrophytic Space between fuels
What are the climatic conditions of wildfires?
Heatwave, Drought, Strong dry winds, Seasonal, El Nino/LOD, Global warming
What are the fuels of wildfires?
Trees, Leaf Litter, Grass, Peat, Fire promoting vegetation - Eucalyptus tree, human built structures (wood)
What impact do slopes have on wildfires?
“Fires on a 20% slope will advance at up to 4 times faster than one on flat ground”
Why do “fires on a 20% advance at up to 4 times faster than one on flat ground”?
Because land and field upslope is pre-heated and therefore catches fire quicker
When is the Harmattan season?
A season in the west-africana subcontinent which occurs between the ens of November and middle of march.
What is the Harmattan season?
It is characterised by the dry and dusty northeasterly trade winds which blows from the Sahara’s desert over West Africa into the Gulf of Guinea
Why does high moisture content prevent wildfires?
Prevents ignition and slows propagation
Why are dense forests less susceptible to wildfires?
They provide more shade, resulting in lower ambient temperatures and greater humidity
Why does less dense forests catch fire easily?
They contain less water than denser material such as branches and trunks
How may evapotranspiration impact the carbon cycle?
Plants lose water through evapotranspiration, which is usually balanced by water absorbed into soil, humidity or rain. When this balance is not maintained, plants dry out and are therefore more flammable, often a consequence or droughts or wildfires (releases mass amount of carbon)
What is a wildfire front?
The portion sustaining continuous flaming combustion, where unburned material meets active flames
At what temperature is wood dried as water is vaporised?
100 degrees
The pyrolysis of wood releases flammable gases 230 degrees
Wood the smoulders at 380 degrees, and can ignite at 590 degrees
At what temperature does the pyrolysis of wood release flammable gases?
230 degrees
At what temperature does the wood smoulder (burn with smoke but no flame)?
380 degrees
At what temperature does the woof ignite?
590 degrees
What temperature can the flames of a wildfire heat the air in front too?
800 degrees through heat transfer from the wildfire front
What are the Indian Ocean Dipole and El Nino?
Climate drivers
What does the IOD refer too?
Year to year tropical sea changes in the Eastern Indian Ocean
What are the three phases the IOD varies between?
Positive, neutral and negative
How often does each phase occur?
Every three to five years on average
When do positive or negative IOD phases occur?
During Autumn or winter
When does a neutral IOD phase occur?
At the end of spring when the northern Australian monsoon arrives
What happens during a neutral IOD phase?
Water from the Pacific flows between the islands of Indonesia, keeping seas to Australias northwest warm, air rises over this area and falls on the western side of the basin - little influence on climate
What happens during a negative phase?
Westerly winds intensify, allowing warmer waters to concentrate near Australia, these stronger winds also it is harder for cool water to rise up from the deep near Indonesia, as warm waters move east the clouds follow bringing rain to Western Australia
What happens during a positive phase?
Westerly winds weaken, and sometimes Easterly winds form, allowing warm water to shift towards Africa, South of Indonesia, these winds allow cold water to rise up from deep areas, with cooler waters and depending air in the Eastern Indian Ocean, less clouds form, less rain in central and southeast Australia
What happens often but not always in Australia?
A positive IOD coincides with the drying influence on the El Nino in the Pacific, both drawing rainfall away from the Pacific
What impacts does the a positive IOD phase coinciding with an El Nino have on Australia?
Failure of crucial winter spring rains and prime the land for severe summer fires seasons
What else can occur at the same time?
A negative IOD with a El Nina
What impacts does a negative IOD phase coinciding with an El Nina have on Australia?
Significant rainfall and widespread flooding
When was the wettest year for Australia?
2010
What is normally happening in the tropical pacific?
The Pacific receives normally easterly trade winds, pushing warm water nearer western side of the ocean near Asia and Australasia
On the east side of the pacific, as warm water gets pushed across, cold water is upwelled, creating a temperature difference across the pacific
What does the El Nino essentially have?
Weakened or reversed trade winds
What happens during El Nino?
Less water is pushed across the Pacific, this means the usually cold parts of the Ocean warm, changing weather patterns over the equatorial Pacific - increase in flooding in Peru and drought in Indonesia
