Hazards: Wildfires Flashcards
(41 cards)
What are wildfires?
An uncontrolled fire, either natural or human- made, that occurs in open country or wilderness.
These are a natural, necessary and beneficial process for many ecosystems.
- Small scale to large scale and widespread.
- Spread rapidly and susceptible to changing direction.
Where do wildfires happen most?
- Boreal forests in Alaska, Canada, Russia, China, Scandinavia •Savannah grasslands in Africa
- Tropical forests in Brazil, SE Asia and Africa
- Temperate forests in U.S., Europe
- Agricultural waste after harvests in U.S., Europe
—> Increasingly (due to climate change) northern latitudes. Boreal forests (coniferous) get less PPT and have a fuel source (peat and deep layers of shed needles).
—> Tropical rainforests often too humid – but recent burning for forest clearance – often gets out of control and spreads for long periods.
—> Mediterranean climate regions: drought-resistant chapparal (shrubs rather than trees) with dry winds.
Why do different ecosystems burn at different temps?
Different ecosystems burn at different temperatures due to the nature & structure of the biomass and its moisture content.
It varies from thin, dry grasses in savannahs to dense, massive trees of the boreal, temperate and tropical forests.
What are the wildfires favourable conditions?
- Dry – often during a long period of drought • Wind
- Low humidity / low precipitation
- Ignitionsource
- Supply of fuel
- Accumulation of dead wood
How does topography make a difference?
- Fires spread quickly on hills as the heat rises.
- Fire can also ‘jump’ across rivers and into areas due to lit debris which causes it to spread.
What are crown fires?
burn the entire tree from bottom to top , which is classed as the most dangerous and destructive type of fire.
- a mild crown surface fire can spread up to 3m per minute
- a massive fire can reach over 100m per minute
What is a surface (brush) fire?
only burn the leaf litter, meaning they are easy to extinguish.
- a small brush fire can spread at the rate of 1m per minute
- an intense fire can spread at over 3m per minute
What is a ground (peat) fire?
e.g. dry peat or vegetation
beneath the surface,
- Slow moving
- Difficult to put out and can actually burn throughout the year if the weather conditions allow it.
- mild fire can start at depths of approx 25cm
- a big fire will burn at a depth of over 25cm
What vegetation type and fuel is needed for a wildfire?
Vegetation should be dry to allow it to catch. Finer vegetation causes fires to spread quicker, but larger, thicker forms of vegetation burns for longer and more intensely.
—> Thick, continuous and densely packed vegetation with trees and thick bushes including vegetation with flammable oils - like eucalyptus.
What climate and weather conditions are needed for a wildfire?
Wildfires occur in a climate that has enough rainfall to have sufficient plant growth , but considerable dry spells and droughts to dry out the fuel . Areas with dry seasons such as California allow for intense wildfires. Wind also causes fires to spread quicker.
—> Prolonged periods of drought and high rates of evapotranspiration, especially in the summer months in sub-tropical climates. A strong dry wind increases the risk.
What fire behaviour is needed for a wildfire?
Fires spread quickly on hills as the heat rises.
- A fire at the base of a long slope with winds moving behind it, up the slope spreads quicker
What’s a key idea for wildfires and climate?
Dry, warm and windy conditions increase fire ignition and their spread.
- Many climatic events can make wildfires grow more intense and extend wildfire seasons.
—> e.g. Katabatic winds like The Santa Ana Winds and Diablo Winds in California cause more wildfire damage.
What is El Niño?
Involves warming of Pacific Ocean off West Coast of South America and affects global patterns of temperature and rainfall. Some places suffer devastating floods or long periods of drought.
Why are wildfires becoming a problem?
- “Forest fires in the western US have been occurring nearly 5x more often since the 1970s and 80s. Such fires are burning more than 6x the land area as before, and lasting almost 5x longer.”
—> Rising temps and drought (lack of rainfall) are two key risk factors.
What are the natural causes of wildfires?
- lightening is particularly likely to start a fire if it occurs without much rain
- volcanic eruptions can produce very hot lava, ash or gas which can start fires
What are some of the human causes of wildfires?
Most fires are started by people
- this can be accidental, e.g. dropping a cigarette, allowing campfires or bbqs to get out of control or fireworks
- it can also be started on purpose, e.g. arson
How is loss of crops, timber and livestock an impact of wildfires?
Fires can particularly affect timber-growing areas as the loss of tree stock will take many years to replace.
—> Jan 2017, 40,000 hectares of pine and eucalyptus plantations were destroyed by forest fires in Chile.
How is loss of life an impact of wildfires?
Although people can get out of the way of most fires, some move so fast that people can be trapped.
—> In Victoria state, Australia, bushfires killed 173 people in 2009.
How is loss of property an impact of wildfires?
With urban expansion, the fringes of towns and cities are now susceptible. The cost of fighting fires from reaching homes can reach millions of dollars.
—> Urban sprawl in Sydney (AUS) and Los Angeles (USA)
How is release of toxic gases and particulates an impact of wildfires?
Large-scale air pollution largely caused by illegal agricultural fires due to slash-and-burn practices.
—> Common in Indonesia. Their 1997/8 event described as the largest forest fire of recorded history. The haze was so big it affected Singapore, Malaysia and Thailand
How is loss of wildlife an impact of wildfires?
Whilst some animals and plants can survive or escape fires, some move fast but some cannot and perish in the flames and smoke.
—> In Indonesia, the fires of 1997 destroyed the Wein River orangutan sanctuary on Kalimantan.
How is damage to soil structure and nutrient content an impact of wildfires?
Extremely hot fires sterilize the upper layer of soils by killing microbial life. They burn off carbon stored in the soil and create water-repellant soils.
—> The 2013 Rim Fire in California burned at 1,450°F (most soils can withstand up to 950°F).
How is evacuation an impact of wildfires?
Many people will flee from an area on fire and not be allowed back in. Emergency shelters and supplies need to be found, often for a long period.
—> In California (Oct-Dec 2017), over 50,000 people have had to be evacuated.
How is increased flood risk an impact of wildfires?
If rain comes in heavy bursts, the loss of so much vegetation and the consequent decrease in interception, can lead to flooding.
—> June 2011, the Las Conchas Wildfire charred more than 150,000 acres in New Mexico. One month later, heavy rains flooded the burn area.
