Wildfire Key Words

• Wildfires- an uncontrolled fire that is wiping out large fields of land

  
  

  • A wildfire moves at speeds of up to 14 miles per hour
  • Ground temperatures can reach over 1000 degrees
  • Wildfires can produce fire tornadoes
  • Every year in the USA, wildfires burn over 5 million acres
• Fire triangle:

  • Oxygen- only 16% O2 is required to make fires
  • Fuel- any kind of combustible material
  • Heat- eliminates moisture from any nearby fuel, warms the air around and prepares the fire path to accept the fire and make it burn with ease
• For a natural fire to star, an ignition source is needed:

  • lightning is the most common natural cause (10-20%)
  • volcanic eruptions and sparks from rocks falling
  • weather events such as droughts and El Ninos
• There are two types of lightning:

  • Cold lightning- stronger electrical current but quicker on the ground
  • Hot lightning- weaker but more time on the ground, more likely to start fires
• Human causes:

  • smoking
  • campfires
  • arsonists- a pyromaniac is somebody who cannot resist setting things on fire
  • slash and burn (subsistence farming)
  • fallen power lines

  90% of forest fires are started by humans
• Types of fires: surface fires, ground fires and crown fires
• Surface fires:

  • most common
  • burn along the forest floor (e.g. leaf litter and branches)
  • burns at around 900 degrees
  • cools quickly, easy to control
• Ground fires:

  • burns organic matter in the soil (e.g. peat)
  • burn at fairly low temperatures (540 degrees)
  • burns for a long time, difficult to put out
• Crown fires:

  • burns through canopy, loose bark allows the fire to spread up the trunk and get into the canopy- the 'ladder effect'
  • temperature in excess of 1100 degrees
  • affects the whole forest
  • most difficult to control
• Spot fires:

  • winds can blow firebrands away from the crown into new areas
  • Firebrands- like fireballs that fly away from burning treetops to other new places resulting in new fires
• Conflagration:

  • large fire which destroys a large area
  • usually enhanced with wind action and firebrands
• Risk has increased sue to population growth and more people moving to rural areas
• Wildfires cause a positive feedback loop: they release carbon stored in vegetation, enhancing the greenhouse effect and increasing the likelihood of wildfires
• The type and amount of fuel influences the intensity and rate of spread (e.g. grassland fires rarely produce the same intensity as forest fires)
• Strong, dry winds blowing from continental interiors or deserts help the drying process and are ideal conditions for lightning storms
• Wind strength determines the rate of spread
• Heat transfer processes (radiation. connduction, convection) preheat trees, forest litter and vegatation ahead of the flames, enabling rapid spread of the fire through spot fires
• El Nino is a climate cycle in the Pacific Ocean with a global impact on weather patterns.

  Normally trade winds blow East to West in the tropical Pacific. During El Nino, the trade winds relax, cutting off the supply of cool water to the sea surface

  The result is a pool of unusually warm and nutritient poor water in the East Pacific. This shifts rainfall patterns

  Australia is dryer than usual, raising the risk of droughts, wildfires and coral bleaching.
• Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperature between 2 areas- the Arabian Sea and Eastern Indian Ocean south of Indonesia.

  The IOD affects the climate of Australia and other countries that surround the Indian Ocean Basin, and is a significant contributor to rainfall variability in this region