Phases of wildfires Preignition (energy absorbing) Preheating – drying out Pyrolysis – chemical degradation Combustion (energy liberating) Fire triangle in place

All components must be present for fire to occur Fire triangle All components must be present for fire to occur

Why wood burns Wet wood – high heat capacity of water absorbs heat making the wood difficult to ignite Once dry it ignites at 572°F, its flash point Flammable gases given off

Conditions for wildfire Plant material + oxygen + heat Combustion equation

How to fight fire Remove or reduce one component Water – reduces heat Slurry – blocks oxygen Remove fuel Cut or clear area Light backfire

Ladder fuel effect

What spreads fire? Fuel types Weather and wind Topography Its own behavior

Types of fuel and results Grass, trees, shrubs, slash piles, homes Rapid advance Grass fires: about 4 mph with 6-8 ft flames Shrub fires: oily material 8 mph, 50 ft flames Understory fuel source important No litter  little damage, fast moving Lots of litter  hot, damaging fire Ladder fuels  crown fires

Flat topography; no wind Flat topography; wind Hillslope and wind

Smoke plume – these can produce the fire’s own weather What is the primary heat moving process here?

Types of fires Ground fire Creep along, mainly smolders, few flames

Surface fires Variable intensity Burns low vegetation and lower parts of trees

Crown fires Burns upper parts of trees Can produce firestorm Move rapidly Impossible to stop

Results of crown fire Coconino National Forest

Causes of wildfires Human caused (85%) Naturally caused (15%) Arson – 26% Equipment – 10% Juveniles - 4% Campfires – 3% Railroads – 3% Other/unknown – 50% Naturally caused (15%)

One day – two BIG fires Oct 8, 1871 Extremely windy conditions affect both areas Peshtigo, WI 15 mile wide fire front Traveled 40 miles northward 1,152 died Chicago, IL O’Leary barn caught fire 300 died 3.3 sq mi destroyed

Weather that produced winds

Extent of Peshtigo fires

Central Chicago following fire

California Chaparral – shrubland plant community; contains a lot of oily, dried vegetation Fires occur every year Major fires in 1991 Oakland and Berkeley Hills 25 died, 2,449 homes destroyed; 437 apts “only” 1,600 acres but $1.5 billion damage Caused by cooking fires in a camp set up by homeless people

Oakland fires in 1991

California fires Santa Ana winds Common October to March High pressure over Nevada Cool, dry air descends over mtns Air heats up, generating winds

Major fires due to Santa Ana winds October/November 1993 Santa Ana winds 15 major fires in southern California 3 dead, 1,150 homes, $1 billion damage 215,000 acres [300 sq mi] October/November 2007 Mexico border to Santa Barbara 350,000 homes evacuated >500,000 acres burned > 2,100 homes destroyed

October/November 2008 August 2009 Santa Ana winds Fires in Montecito, Sylmar Montecito fire due to bonfire Interstates closed More than 1,200 homes destroyed Almost 50,000 acres August 2009 Station Fire, 161,000 acres NE of Pasadena Arson caused

Fire suppression 20th century approach – put fires out!! Trees per acre increased dramatically In 1970s decision was to let fires started naturally burn; human-caused extinguished Prescribed burns Formerly “controlled burns” Los Alamos, NM, burned in May 2000; 280 homes destroyed

Yellowstone National Park Burn areas shaded Dry winter in 1987-88 Low moisture content and many beetle ridden trees Fires began in June and July 1988 By mid-August very dry and fire lasted until Nov 1.4 million acres burned, about half of the park Natural-burn policy in place since 1976

Rodeo-Chediski Fire of June 2002 Two separate fires grew together; 5,000 firefighters More than 500 homes burned; 732 sq mi destroyed

Wallow Fire May and June 2011 Largest fire in AZ history burned 538,000 acres, including 15,000 acres in New Mexico Caused by campfire lit by two cousins

Aftermath of fires Rejuvenation of land naturally due to released nutrients and opening of seeds replanting Erosion and landslides Formation of hydrophobic layer caused by oils and organic compounds vaporizing and recondensing in cooler layers under the surface Expense to fight fires Fiscal cost Loss of life Reduced air quality

Schultz Fire north of Flagstaff June 20, 2010 burned 15,000 acres

Extremely high winds rapidly spread fire caused by a campfire

Area north of Flagstaff following 1996 fire

Summary Good: Increase in soil nutrients and regeneration of vegetation (aspen, conifers) Reduction of potentially larger fires Bad: More erosion, runoff, mass wasting, loss of life (human and animal)

What is there to learn? Restrict development in heavily forested areas Decrease fuel sources with prescribed burns Undertake preventative measures through education

A healthy forest