Phases of wildfires Preignition energy absorbing Preheating drying

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

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%) – 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 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 – 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 • 20 th century approach – put fires out!! • Trees per acre increased dramatically • In 1970 s 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

• Burn areas shaded Yellowstone National Park 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