Wildfires

• Fires are a natural process and can be beneficial (stimulates growth of plants and aid new seed germination).
• Temperatures of the ground can rise to over 1000 degrees celsius.

  Surface fires are on the ground and canopy fires are on the canopy.
• Nature of the fire depends on:

  • Type of plants
  • Strength of the wind
  • Topography of the area
  • Behaviour of the fire
• Large fires are in dry, windy weather - strong winds in dry vegetation causes embers to set more fires.
• Retardants - chemicals sprayed onto fires to slow them down: nitrates, ammonia, phosphates, sulphates and thickening agents.
• Pyrophytic vegetation - pyrophytes are plants adapted to tolerate fire e.g. baobab tree - semi-arid grassland
• Methods of survival: thick bark, tissue with high moisture content and underground storage structures.
• Causes:

  Ignition - natural or manmade e.g. lightning, cigarettes, BBQs, arson, 300 degrees celsius flashpoint

  Fuel - quantity, dry, litter, drought e.g. trees, vegetation, homes, grass
• Fire triangle: fuel, oxygen, heat source
• Distribution:

  • Essentially a rural hazard
  • Urbanisation: California, Australia, countries of Southern Europe: vulnerable to wildfires - prone to high pressure
  • California: more media coverage - threatens celebrity homes
  • LA: covered by drought-resistant chaparral, dry wind (Santa Ana) - increases dryness of vegetation, low-density building, tinder dry vegetation, sparsely populated areas
• • More than 100,000 wildfires in the US per year
  • Clear millions of hectares of land
  • Move up to 14 miles per hour
  • Flashpoint - 300 degrees celsius
• Effects:

  • Loss of crops, timber and livestock
  • Loss of wildlife
  • Economic loss - $10 million a day fighting wildfires
  • Loss of life
  • Loss of property - suburban at risk, leads to homelessness
  • Damage to soil structure and nutrient content
  • Release of toxic gases and particulates
• Secondary effects:

  • Evacuation - sometimes permanently
  • Increased flood risk - loss of vegetation
• Preparedness, mitigation and prevention:

  • Managing vegetation
  • Managing built environment - more stone than wood, spark arresters in chimney
  • Modelling - computer simulations to predict fire behaviour
  • Education
  • Warning systems
  • Being well insured - can be expensive in fire prone areas
• 90% of woodland fires are caused by people