Wildfires

LAST MODIFIED:

POSTED: 10 June 2020

• Fire and the Human Race

• control and use fire major factor in development of human race
• important means of preparing food
• fire directs game animals as well as predators
• slash-and-burn clearing of forests to gain land for agriculture
• ash serves as fertilizer
• hardens material from pottery through weapons
• ultimately initiated industrial revolution



• What is Fire?

• rapid combination of oxygen with organic material in a reaction that produces flames, heat and light
• organic material is heated above its point of combustion
• fire can be understood as photosynthesis reversed
• input: cellulose, O2 --output: heat, CO2, H2O



• What causes Wildfires?

• about 1800 thunderstorms are in action around the Earth each hour
• 8.6 Mio cloud-to-ground lightning strikes each day⁽¹⁾ and some lightning strikes initiate fire
• in the U.S. lightning strikes start about 15% of all wildfires
• the rest are caused by human action
• the number of deaths by fire has declined by a factor 2 in the last 20 years while the value of damaged structures has tripled



• Stages of Fire

• 1) preheating phase: H2O expelled (H2O has high heat capacity!)
• 2) pyrolysis: chemical structure of wood breaks down; flammable hydrocarbon vapors ignite if O2 is present
• 3) flaming combustion: consumption of gases (hot)
• 4) glowing combustion: consumption of wood (less hot)

the underlying chemical process to combustion is oxidation, i.e. oxygen is used in the process.



• The Spread of Fire

• since hot air rises rather than sinks, fires burn more effectively uphill than downhill
• however, if pushed by winds - e.g. Santa Ana winds - fires can quickly spread downhill



• The Fire Triangle (and how to fight fires)

Fighting a fire involved the reduction (or removal) of one or more sides of the fire triangle:
• fuel: vegetation to feed fire (clear vegetation; back fires)
• oxygen: needed for process of combustion (air tankers drop reddish fire retardant)
• heat: aids stage 1/preheating phase of a fire (water reduces heat)



• Fuel

• grass; fires move at 6.5km/h (4mph); flames 2.5m (8ft) high
• shrubs: 15km/h (8mph); flames 15m (50ft) high most intense when plants contain natural oils
• trees: damage depends on how much shrubs is present; can jump into tree crowns causing fast-moving crown fires



• slash: woody debris after a forest has been clear-cut
• duff: 1ft thick bed of pine needles; can looks extinguished but smolders inside getting hotter until combustion ignites new fire



• ladder fuel: combination of all of the above; creates major wildfires



• Why does Nature Need Fires?

• for recycling of organic material in unfavorable climates
• germination
• pest control
• to influence insect behavior (e.g. pollination)



• Climates that do not need fires for recycling organic material

• tropical (warmth and moisture abundant for effective decomposition)
• desert (plant growth too slow)
• polar region (plants not abundant)



• Climates that need fires for recycling organic material

• grasslands
• seasonal tropical forest
• some temperate-climate forests
• Mediterranean-climate shrublands
  (winters too cold, summers too hot for effective decomposition)



• Examples of Plants that Need Fire to Reproduce by Seeds

• Lodgepole Pine: (6-24 m height; 0.3-0.9 m diameter) occurs in three subspecies along the coast and inland areas of western North America from Alaska to California. It is the only conifer native to both Alaska and Mexico. The bark is thin and trees grow densely packed, next to each other, and Dead trees serve as ladder fuel, all this allowing for fires to spread easily into the crowns and between trees. Lodgepole pines need these fires to regenerate in the post-burn areas. Fires in these forests are relatively rare (due to the lack of understory vegetation) but intense. Cones remain closed until the heat of a fire opens them, allowing the growth of a new forest.
• Knobcone Pine: (9-24 m height; 0.3-0.8 m diameter) occurs along the coast and inland of western North America between Oregon and Baja California. Forms almost pure stands on poor, coarse, rocky mountain soil. The cones may become embedded in the trunk when the tree grows. When fires kills the trees, cones as much as 30 years old are opened by the heat and shed their seeds.



• How does Nature Cope with Fires?

some plants take protective measures, e.g. the two members of the Redwood family; both are among the oldest trees in the world (can get more than 3500 years old)
• Redwood (sequoia sempervirens); tallest tree; wood intrinsically fire resistant
• Giant Sequoia (sequoia gigantea); largest tree; thick spongy bark protects against fire; can be burned partially and still survive small fires
• both trees found in the Sierra Nevada



• "Weather" caused by Fire/Some Burn Features

• convection column/convection plume
• burns quickly upslope (e.g. try holding a match head-up and head tilted down)
• particularly hot near top of slope
• causes updraft on other side of hill
• fire tornadoes; see an example at the NOAA website
• flying embers when high winds, causing new fires far away



• Fire Risk caused by Weather

• cold front winds
• local winds (e.g. sea breeze, land breeze, slope winds, valley winds)
• Foehn Winds (called Santa Ana in Southern California, see below)
• high-pressure air spilling over mountain range then descending as warm dry wind
• in U.S. Great Basin, this typically occurs from September - February; however, some are as late as April, or even May (2014 in San Diego)
• especially strong when low pressure system sits on the other side
• have different names for different areas (Chinook, Diablo, Santa Ana, East, North)
• wind gusts up to 50 mph; extremely low humidity (<20%)
• fires often come in clusters



• Dangerous Weather Condition in Southern California

• In Southern California, Santa Ana weather conditions lead to
  • high temperatures
  • strong winds
  • extremely low humidity
• Santa Anas occur mostly from September through February
• tremendously increases the fire risk in San Diego's back country
• fire risk particularly severe before first big winter storms drenched the back country (i.e. through end of October/early November)
• fires that are otherwise easy to fight, readily burn out of control in a short time
• fires very often come in clusters; this can spell disaster for San Diego when fires have broken out in the north and resources are sent to help out. Resources may be limited by the time fires break out in San Diego County. Apart from limited resources, communications breakdown between the city of San Diego and the county (2003 fires) and civil and military firefighters (2007 fires) have hampered efficient fire fighting.
• MOST IMPORTANTLY: pushed by Santa Ana winds, such fires are nearly impossible to fight and contain. Fire fighters often get the upper hand only after winds shift/Santa Anas die down.

• Fuel in Southern California

• chaparral:
• perennial evergreen brush, e.g. manzanitas
• one of most flammable plant groups (some contain aromatic oils)
• some need heat or smoke to germinate
• can grow shoots from unburned subsurface roots
NB: no-one appears to have successfully grown manzanitas from seeds; it is thought that the wild population has mostly propagated through shoots
• eucalyptus:
• in urban areas, e.g. UCSD, Scripps Ranch
• native to Australia, introduced in San Diego
• aromatic oils increase fire risk
• fast growing
• low-quality brittle wood
NB: made headlines in the 2003 Cedar Fire when parts of Scripps Ranch burned down. Interestingly, photos show that many homes burned but the eucalyptus trees next to them remained green.
• pines:
• particularly rich in flammable resins
• some need heat or smoke to germinate
• palm trees:
• usually not listed as vegetation that would increase fire hazard
• however, may have increased production of embers
NB: in the 2007 Witch Creek Fire, palm trees burned liked sparklers, with embers picked up and carried by Santa Ana winds, igniting homes 5 miles away from the fire line



• The Role of Strong El Niños and other Wet Winters

• strong El Niños cause above normal annual rainfalls
• the 1997/1998 El Nino was one of the strongest in the century
• unusually late start of the rainy season
• strongest rain March/April, when plants in mountains start growing
• unusually lush vegetation that died in following years
• unusually large amount of fire fuel
• the 1997/98 El Niño set the stage for the 2003 fires
• 2004/2005, the third-wettest winter on record (22.5 in season total; with a strong Pineapple Express in January 05) set the stage for the 2007 fires



• Fire Fighting or Suppression? The Case California

a comparison of fires in California and Baja California also reveals that fire fighting practices do not decrease the amount of area burnt

• California fights fires at any cost while Baja lets them burn
• in Baja half the area burnt in twice as many fires; i.e. CA fires much bigger
• only 20% of fires in Baja burn after Sep 1 (start of Santa Ana season), while 72% burn in California; i.e. Santa Ana fire risk increased in CA!


• fire fighting efforts brought the # of fires down, but the total acreage burned increased
• this means that, on average, fires are becoming larger and more difficult/costly to fight
• should forests be thinned (decrease of shrub growth -> decreased fire risk!?)
• should fires be allowed to burn? (could go out of control)
• are prescribed fires the solution? (number is increasing, so is cost)
• WHO PAYS FOR THIS?



• Housing in Southern California

Reasons why our house may be the next one, and measures we can take to lower that risk.


increases risk	protective measure
house built above a canyon edge	set house back by 100ft
wooden deck overhanging edge of canyon	see above
lots of dead brush on the slope below the house	clean up brush; plant ice plants
trees and brush touching/overhanging the house	clear brush 30 ft around the house
Pine trees and eucalyptus trees near house	plant less burnable, native trees
fire wood stored next to house	store wood away from house
wood shingle roofing	tile or composite roofing
shingle or other wood siding	spray stucco
far-reaching eaves	boxed eaves that do not extend far beyond house
large, single-pane windows facing the canyon	smaller windows
no spark arrester on chimney	install spark arrester
narrow driveway	wide driveway to allow access by fire trucks

CASE STUDIES

• CASE STUDY 1: 1910 Bitterroot Mountains and the Beginning of Fire Suppression

• known as the Big Blowup, a fire in August 1910 burned over 3 million acres in Idaho and Montana
• 85 fatalities
• US Congress authorized expenditure of federal money to fight forest fires
• policies and training since have been to fight and suppress fires as much as possible
• therefore, acreage burned in wildland fires has decreased from over 26 million acres in the 1920s to only a few million acres in the last 5 decades
• as a result, forests have become much denser; before suppression: 30 big trees per acre; now, 300 - 3000 big tree per acre plus understory in some forests
• when lightning now ignite forest fires, they burn hot and slow, killing the big trees

• CASE STUDY 2: Yellowstone Park: Fire Fighting or Suppression?

simple fire suppression without other supplemental measures decreases the amount of small fires but increases the risk of a huge fire that can burn out of control (see above). A prominent example is the big fire disaster of 1988 in Yellowstone National Park:

• oldest National Park in U.S. (1872)
• fires had been suppressed since the beginning
• 1970s change in policy: let natural fires burn; fight human-induced fires
• was ok for 17 years; e.g. 1976-1987 saw 235 small lightning-induced (100 acres) fires; the largest burning 7,400 acres


• then dry spell in 1988 (dry winter season)
• forest was in serious state: tree kill by Mtn. Pine beetle since 1960s; 9 decades of fire suppression allowed extensive build-up of deadwood; dead wood dried out from typically 10-25% to 7-2% water
• lightning started fire in June 88
• decision to fight fire after 8,500 acres had been burnt
• adverse weather (heat wave) let fire burn out of control (Aug 20 burned 150,000 acres of park in 24h; more than total in preceding 116 years (146,000 acres)
• fire only ceased after snow started to fall in November
• loss of 345 elk, 36 deer, 12 moose, 9 bisons, 6 black bears
• burned area: 790,000 acres (36% of park)



• CASE STUDY 3: California's Worst Fires: The Cedar, Paradise and Otay Fires on the Weekend of October 26 2003?

preceding the weekend of the tragic Cedar/Paradise and Otay fires, a number of factors had dramatically increased the fire risk in San Diego county in recent years:

• 1997/1998 strong El Nino; San Diego received 2-3 times normal rain fall
• succeeding La Nina dried out countryside
• warning that "next 10 years will be dry"
• last 5 years below-average rainfall
• threat of MAJOR wildfires; but did not happen
• 2002 Pines Fire east of Julian (helicopter downed power line) only major fire
• explosive development of city into rural areas (Scripps Ranch faces several chaparral-loaded slopes)

extraordinary circumstances just before the weekend left San Diego practically defenseless

• Red Flag Weather Warning on Oct 24! SANTA ANA!!
• Fires had been burning in Camp Pendleton; Simi Valley; St. Bernardino (Santa Ana clusters fires!)
• California sends fire fighters were they are needed, so S.D. had only few
• a lost hunter is thought to have started the Cedar Fire
• the Cedar fire started near Ramona and the San Diego County Estates and went quickly out of control
• nature-induced spread: after burning for 6-7h, Santa Ana winds pushed fire out of control; fire spread west extremely fast (some estimates are > 15mi in less than 1h before it reached Scripps Ranch early Sunday morning)
• human-induced spread: spread of fire might have been delayed if air support had been allowed to fly closer to sunset; miscommunication between county and city; too few fire fighters; Otay fire initially unattended because it didn't immediately threat homes.

By the end of Sunday, the winds died and shifted. By Monday the fires did no longer threat the city by which time new coverage diminished significantly. The Cedar Fire alone had burned 194,000 acres in the first 31h, 2/3 of the total area burnt in this fire.
The fire had also burned toward the east and was spreading faster after the winds shifted. The fire became more intense because it now burned into the forest were fuel included trees. The fire had reached Cuyamaca by Wednesday, October 29 - despite a tremendous increase of fire fighting resources - and Sunrise Highway that leads to the the Mount Laguna area a day later. The historic part of Julian was spared but a large fraction of the houses in the area burned. The total area burned was 280,000 acres in the Cedar Fire alone (total of nearly 400,000 acres in all three fires). The worst preceding fire in terms of acreage burned was the 1971 (or 1970?) Mtn Laguna Fire that destroyed 108,000 acres.
Though the loss of homes caused tremendous heartache, the city will recover sooner than later, perhaps just in a few years. The surrounding wildland will need significantly longer. While grass started to grow during the flowing winter season, estimates are that shrublands need in excess of a decade for full recovery. Wooded areas, such as the Silverwood Wildlife Sanctuary of the National Audubon Society, will need at least three decades and the forests in the Cuyamaca area probably longer ... an awfully long time in a human lifespan ... but nothing really for Nature.
See also the summary on the Santa Ana page and links to the 2003 fires and 2007 fires.



• How Can we Avoid this to Happen Again?

Good question! The problem is very complex and there is probably no perfect solution. If fact, some suggests are impossible to realize, and perhaps some shouldn't! They include:


• ice plants everywhere! (not native to San Diego; does not support wildlife)
• change air support flying rules (put fire fighters in harms way?)
• better communication between City and County emergency crews
• change California fire fighter exchange rule (though would we suggest the same if the Cedar Fire had started before the Grand Prix Fire in St. Bernardino?)
• better house protection (no guarantee! Some house were lost despite all the right efforts)
• buy more helicopters (who pays for this? The current sole San Diego fire fighting helicopter costs $200,000/month; the purchase of one would involve $1.5Mio)
• stop urban sprawl?
• more prescribed fires (who pays for this? Some burn out of control, e.g. Los Alamos 2000!)

NB: Update on October 2008: A week short of the 4th anniversary of the Cedar Fire, San Diego county was again struck by devastating wildfires in October 2007 (Witch Creek, Guejito, Rice, Harris Fires). The city then got a second helicopter (split-funded with SDG&E??) and communication and coordination with the military was promised to improve (the latter was poor in both fires). Proposition A on San Diego County's Nov 04, 2008 ballot calls for an addendum to the property tax (countywide parcel tax) to fund a new Regional Fire Protection Agency to coordinate fire fighting and prevention (50%) and to augment services at existing local fire agencies (50%).
Update 2010: the proposition was defeated with 63.25% of the vote. check out at ballotpedia.org

1. 5%
2. 15%
3. 25%
4. 55%
5. 85%

1. pyrolysis
2. combustion
3. preheating
4. hydrolysis

1. recycling of organic material
2. improve root growth
3. germination
4. pest control

1. winds raise surface temperatures
2. winds dry out potential fuel
3. winds can push fires out of control
4. all of the above
5. b) and c)

1. always
2. when it rains
3. when pushed by winds