Climate change and wildfire Flashcards
What is a fire?
Fire is a rapid combination of oxygen with carbon , hydrogen, and other elements of organic material in a reaction that produces flame, heat, and light. Photosynthesis reaction in reverse!
The thermal degradation of wood involves the process of PYROLYSIS.
What is Pyrolysis?
During the process of pyrolysis the chemical structure of solid wood breaks apart and yields flammable hydrocarbon vapors along with water vapor, tar, and mineral residues. If oxygen is present when the temperature is raised, the pyrolysed gases can ignite and combustion begins.
What are wildfires?
Any uncontrolled fires occurring within natural landscapes such as forests. These unpredictable fires have the ability to jump gaps such as road, rivers, and fire lines, making containment and suppression exceedingly difficult.
The fire triangle: important to visualize how to fight fires Three components:
- O2 makes up 21% if the atmosphere
- Heat increases during summer and/or droughts
- Fuel (any combustible material): Given the common presence of oxygen and heat the occurrence of fires is mainly limited by the amount of fuel available
The fire triangle: Ladder fuel
Ladder fuels rare vegetation of varying heights in an area that allows fire to move easily from the ground to the treetops
The stages of fire
1) Preheating phase: water is expelled from plants, wood, or fossil fueled by nearby flames, drought, or summer day.
2) Flaming combustion: stage of greatest energy release.
3) Glowing combustion: In a fireplace, the active flames disappear but the wood surface glow. This is a slower process of oxidation of the charred remains.
There are four ways heat can be transferred in a fire:
- Convection: through air flowing up and away from the fire
- Radiation: electromagnetic waves
- Conduction: heat is transmitted downward or inward through physical contact
- Diffusion: heat is in particles that move from ho:er to cooler areas.
Three types of wildfire:
1) ground fire: Move slowly along the ground, with glowing combustion playing an important role
2) surface fire: Advance as a wall of fire along a flaming combustion front
3) crown fire: race through the treetops as a crown fire.
The spread of fire: Fire behaviour
1) Fuel (any combustible material):
The energy release in a fire depends on the chemical composition of the plants, etc. being burned.
2) Temperature increase, changes in precipitation, winds (fresh supply of O2)
3) Topography- Fire burns faster up a slope because the convective heat rising from and above the fire front dries out the upslope vegetation in an intense preheating phase
Impacts associates with climate change:
1) An increase in global mean temperature.
2) Changes in precipitation. The distribution of precipitation in space and time is very uneven, leading to tremendous temporal variability in water resources worldwide (Oki et al, 2006).
Wildfires in Europe
• Warmer temperatures
• Increased summer
temperatures
• Early spring- snowpack melt- infiltrate into the soil earlier in the year
• Forests have less summer water source making them more prone to drought and vulnerable to wildfires
Case study -Wildfires in La Gomera, 2012
The fires burnt 18% of the 4000 ha of Garajonay NaDonal Park.
Widely reported as an ‘ecological disaster’ and a ‘severe threat to a UNESCO World Heritage area’. J.Ecol.blog
- 2012, the summer season was one of the driest registered.
- 6 heat waves (temperatures above 30 oC and relative air moisture below 20%) from the Sahara.
- Low rainfall rate along the previous winter and spring.
Past Climate change in Garajanoy National Park
HUMID
Rapid respond to moisture-balance variability
Laurel forest taxa along with Phoenix canariensis and Salix canariensis EXPANSION
DRY
increase of the Macaronesian heath community together with a gradual loss of laurel taxa may be expected.
Increasing fire events and the opening of the forest
Conclusions form La Gomera
- Low frequency of fires for the past 10000 years
- Fire events suggest a climatic shift as regional fires reached their maximum at 4800 cal.yr BP
- Local fires increase at 3000 cal. yr BP. Human arrival?
