Textbook Notes (362,796)
Canada (158,054)
Geography (105)
GG231 (31)
Rob Milne (27)


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Wilfrid Laurier University
Rob Milne

Wildfires ­ look at pg 320 for case study! BC Wildfire: an ancient phenomomenon, dating back more than 350 million years, to the time trees evolved and spread across the land. -Grasses appeared 20 millions years ago, providing fuel for other types of wildfires. -Climate became warmer and perhaps drier than it is today, leading to a marked increase in wildfires ­ Increase in charcoal in sediment dating from the first several thousand years of the Holocene Epoch in Western North America, indicating high wildfire frequency at this time ­ Humans’ use of fire to clear land and assist in hunting Natural fires start by- lighting strikes, and volcanic eruptions, which allowed early humans to harness fire for heat, light and cooking -Wildfire is a self-sustaining, rapid, high temperature biochemical oxidation reaction that releases heat, light, carbon dioxide and other products. -Requires 3 things: Fuel, oxygen and heat (if any removed, fire goes out) Plants remove carbon dioxited by photosynthesis and temporarily sequester carbon in their tissues. Microbes alone do not decompose plant material fast enough to balance the addition of carbon through continued plant growth. Wildfires help to restore this balance Many compounds are released when plants burn in soild, liquid and gaseous forms- common trace gasses include nitrogen oxides, carbonyl sulphide, carbon monoxide, methyl chloride and hydrocarbons such as methane. These gasses form the smoke. -Ash and soot are powdery residues that accumulate after burning -ash consists of mineral compounds and soot is made of unburned carbon Wildfires have three phases: 1) Pre-ignition phase- vegetation is brought to a temperature and water content at which it can ignite and burn. Pre-ignition involves 2 processes, 1a) preheating and 2a) pyrolysis. 1a) Preheating- vegetation is heated as it loses a great deal of water and other volatile (easily vaporized) chemical compound 2b) Pyrolysis- “heat divided- a group of processes that chemically degrade the preheated fuel. Degration takes place as heat splits large hydrocarbon molecules into smaller ones. Products of pyrolysis include= volatile gases, mineral ash, and tars. ­ these two process operate continuously in a fire 2) Combustion- involves external reactions that liberate energy in the form of heat and light. -Flaming Combustion- the rapid, high-temperature conversion of fuel to thermal energy by oxidation reactions. Leaves a large amount of residual unburned material. Sustains flames. - Glowing or smouldering combustion- take place at lower temperature and does not require rapid pyrolysis. Volatile gases are removed from the fuel, woody material continues to burn, but the amount of fuel is less and ash begins to cover new fuel. 3 primary processes control the transfer of heat as a wildfire moves across the land: CONDUCTION- the transmission of heath through molecular contact RADITATION- heat transfer by electromagnetic waves CONVECTION- heat transfer by the movement of heated gases drive by temperature differences in a liquid or gas. 3)Extinction- the point at which combustion including smouldering, ceases. A fire is considered extinct when it no longer has sufficient heat and fuel to sustain it Case study- Indonesian Fires 1997-1998 -sever wildfires on island of Borneo and Sumatra brought international attention to Indonesia - many fires produced to clear land but were worsened by a long drought cased by a strong El NINO event -burned about 100 000 km2 of forest, an area larger than New Brunswick - so much smoke, caused inonesia, Malaysia and Singapore to be blanked “haze” . Caused economical and health issues FIRE ENVIRONMENT: the behavior of a large wildfire can be explain by 3 factors: 1)
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