conditions to a wildfire

• There are certain conditions that, when combined, are likely to result in a wildfire:

  Fuel (usually in the form of dry vegetation)

  Heat/Ignition Source (natural and human)

  • Oxygen and favourable climatic/weather conditions
• The behaviour of a wildfire (speed and direction of movement) is dependent on the type of vegetation (fuel), the climatic characteristics and the local topography (slopes, valleys, etc.)
• What conditions favour wildfires? 

  • Climate and weather conditions: 
  • Vegetation type
• Vegetation type – the fuel characteristics: 

  • The type and amount of fuel influences the intensity of the wildfire (the output of heat energy) and the rate of spread (degree of threat). Grassland fires rarely produce the same intensity and degree of threat as forest fires. 
  • Different types of vegetation will result in higher/lower intensity fires – e.g. leaf litter, grass, peat etc. 
• Grasslands are large areas where the primary vegetation type found is long grasses. 

  These ecosystems are common in many areas around the world with warm and seasonally dry periods, such as part of the USA, Australia and many countries in Africa.

  Grass can dry out quickly in warm dry conditions. Due to its large surface area to mass ratio, when dry it can burn very easily. Large grassland areas can also promote strong wind if their topography is flat and unobstructed.

  
• Leaf litter is the material that is dropped to the floor by vegetation. It is able to dry out quickly once cut off from the moisture supply of the plant. 

  Large quantities of dry, leaf litter can provide and excellent tinder for forest fires to start from. Obviously, forests can often have large quantities of leaf litter due to the abundance of trees.

  Some forests have trees that provide leaves that are packed full of natural oils, these can burn even more easily and ferociously.
• Eucalyptus trees are native to Australia and their oil can make them an excellent fuel for forest fires.
• Peat is an accumulation of partially decayed vegetation or organic matter. Therefore it is found in the ground, below the surface.

  It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem is the most efficient carbon sink on the planet, because peatland plants capture CO2 naturally released from the peat, maintaining an equilibrium.

  Peat is used a fuel source in many places around the world - in Ireland they burn it on their stoves and fireplaces as it was a locally available fuel.

  
• Climate and weather conditions: 

  • Heatwaves, droughts and cyclical climatic events (e.g. El Nino) create favourable conditions for wildfires. Most wildfires occur during or after prolonged dry periods – when the vegetation is at its most combustible. 
  • Strong, dry winds blowing from continental interiors or deserts exacerbate the drying process – ideal conditions for lightning storms (a common form of wildfire ignition)
• Heatwaves are prolonged periods of unusually hot weather that are often accompanied with little or no precipitation. In warmer heatwaves, evaporation rates can increase to a high level leaving the ground and vegetation in the area extremely dry. 
• Santa Ana Winds – southern California

  1. Desert winds originate from a clockwise flow of air around a high-pressure system east of the Sierra Nevada mountains. 
  2. Air from the mountains is compressed and warmed, becoming less humid. This dries out vegetation and can fan any existing fires.
  3. Winds squeeze through canyons with gusts between 65 and 95 km/h. 

  Strong winds create turbulence and can make interstate travel difficult.
• El Nino is a cyclical condition that occurs approx. every 6-8 years in the Pacific Ocean. It involves the warming of the ocean off the west coast of South America and affects global patterns of temperature and rainfall.
• Australia’s Black Saturday wildfire (Feb 2009) coincided with another cyclical event called the Indian Ocean Dipole (IOD) – an ocean and atmosphere phenomenon that affects the climate of countries that surround the Indian Ocean basin. 

  During a positive IOD period (cooler than normal water in the tropical east and warmer than normal water in the tropical west), there tends to be a decrease in rainfall over parts of central an southern Australia, therefore increasing the risk of wildfires.
• Global warming is the term we use to refer to the atmospheric changes that are currently taking place globally that are leading to planet Earth having a warmer climate on average. 

  We know this has occurred naturally through out Earth’s history, but humans have accelerated the warming process since their industrialisation.
• Scientists have discovered recently that selective logging of the Australian forests has actually led to making the wildfires they have experienced worse.

  By thinning the trees and removing a select few from within the forest, you reduce the forests ability to retain moisture, allowing it to dry out more quickly. Fewer trees also reduces the canopy cover shading the ground, allowing leaf litter to dry out more quickly.