Natural Hazards and Disasters Chapter 16 Wildfires

1. Natural Hazards and Disasters Chapter 16 Wildfires

2. A Deadly Wildfire Firefighters recognized danger in Storm King fire in Colorado Smokejumpers moved up ridge as fast as possible, just ahead of fire Other firefighters could not outrun fire – burned upslope at 2 m/s 14 firefighters died, some just steps away from safety

3. Fire Process and Behavior • Wildland fires are natural part of forest evolution • Benefit ecosystems by • Thinning forests • Reducing understory fuel • Permitting growth of different species and age groups of trees • Factors that affect wildfire behavior are • Fuel • Weather • Topography

4. Fuel • Fire requires three components • Fuel • Oxygen • Heat • Type of fuel available, its distribution and moisture content determine how quickly fire ignites and spreads • Fuel loading is amount of burnable material

5. Fuel • Primary sources are trees and dry vegetation • Burn at high temperature by reaction with oxygen in air • Cellulose: compound of carbon, hydrogen and oxygen • Breaks down to carbon dioxide, water and heat • Natural oils and saps add to combustibles • Large relative surface area accelerates ignition and burning • Heavy fuels with small surface area ignite with difficulty and burn slowly

6. Fuel Ladder fuels: low brush and branches that ignite first and allow fire to climb into higher treetops Crown fire burns through treetops with incredible speed and heat

7. Ignition and Spreading • Fires can be • Naturally started by lightning strikes (13%) • Intentionally set for beneficial purposes (24%) • Set accidentally or maliciously (26%) • Fires ignite and progress by • Radiation • Convection • Firebrands or burning embers • Firebrands carried by wind ignite spot fires

8. Topography • Local topography can • Funnel air • Accelerate fire • Cause more rapid spreading • Chimney-like funneling effect in canyons and on hillsides • Fires generally move rapidly upslope and slowly downslope

9. Weather Conditions • Fires start more easily and spread rapidly during dry weather with low fuel moisture • Few years of less than normal moisture: dehydrates soil, lowers water table, providing less moisture for vegetation • Winds accelerate fires by • Directing flames at new fuels • Bringing in new oxygen • High winds or extreme amounts of dry fuel can initiate firestorms that generate their own winds as convective updraft

10. Secondary Effects of Wildfires • Major fire can lead to other hazards • Floods • Landslides • Sometimes more disastrous than fire itself

11. Erosion Following Fire Organic material burns into hydrocarbon residue that soaks into ground Water can no longer infiltrate surface soils Most water runs off hydrophobic soils, carries fine grains downslope as sheetwash or overland flow Unprotected soils are easily gullied Flow can turn into flash flood or debris flow

12. Mitigation of Erosion Erosion following fire can not be prevented but can be minimized Plant vegetation, grass, shrubs and trees that prevent direct impact of raindrops on bare soil Slopes are seeded after fire Tubes of straw or straw bales can provide to overland flow Sheets of plastic prevent water from reaching soil

13. Wildfire Management and Mitigation • Wildfires are necessary to evolution of forest ecosystems • From 1985 to 1994: • Average of 73,000 fires per year on federal lands • More than 3,000,000 acres • $411 million cost of fire suppression • More people move to forest, range and other wildlands

14. Government Policy • U.S. Forest Service was formed in response to catastrophic wildfire in northern Idaho and western Montana in summer 1910 • Policy was to aggressively fight wildfires • U.S. spends more than $1 billion per year, with no long term benefit • Preventing fires leads to buildup of wildland fuels  worse fires • Shift to mitigation and management of fires • Prescribed burns to remove fuel • Wildfires permitted to burn in wilderness areas

15. Fighting Wildfires Smokejumpers parachute into remote areas to exterminate lightning fires before they spread out of control Bulldozers cut firebreaks to remove vegetation Aircraft drop water or fire retardant along advancing edges of fires Firefighters cut fire lines to prevent spread of fire Deliberately-set burnout fire burns back toward main fire, eliminating its fuel

16. Fighting Wildfires

17. Risk Assessments and Warnings • Vegetation and topography can increase risk of fire • Weather patterns that affect wind direction or moisture influence fire risk • Fire weather potential depends on • Number of high-temperature days • Relative humidity of air • Moisture in available fuels (using drought maps) • Wind speed

18. Protecting Homes from Fire People live in woods to get away from urban congestion and for beauty of nature Put themselves and property in danger Compulsion for officials to protect individual properties rather than managing overall fire Forest homes or homes at urban interface are at risk, if built from flammable materials and surrounded by ground fuels

19. Protecting Homes from Fire Firebrands from crown fires can easily ignite flammable rooftops and decks Ground fuel often ignites homes, leaving surroundings trees and fences unburnt Radiant heat from burning trees can ignite home up to 30 meters away Government regulations on building materials can mitigate damage in future fires

20. Public Cost of Fires • Zoning restrictions considered unacceptable infringement of people’s property freedoms • Some build in indefensible locations, such as narrow canyons • Insurance companies set premiums based on risk and replacements costs • Federal and state governments pay cost of fighting fires, cleanup, and some of rebuilding • Insurance companies require homeowners to clear brush, cut down trees, install fireproof roof • Also dramatically increasing insurance premiums • FEMA beginning to help people to relocate to more suitable locations • Alternative is to make clear that those who choose to live in vulnerable areas can not expect public help

21. Case in Point Debris Flows Follow a Tragic Fire: Storm King Fire, Colorado, 1994 Dry lightning storms ignited 40 fires in two days Cold front lowered humidity and caused strong, erratic winds in shear vortex of 65-80 km/hr Fourteen firefighters were overrun and killed as they tried to run upslope to escape fast-moving fire In weeks after fire, rain washed ash and dirt downslope to accumulate in drainage channels Heavy rains mobilized loose material into debris flows One debris flow washed across Interstate 70, engulfing 30 cars but killing no one

22. Case in Point Firestorms Threaten a Major City: Southern California Firestorms, 2003 and 2007 Hot, dry Santa Ana winds blew westward out of desert at up to 100 km/hr in October 2003 Within ten days, eleven major fires had burned 3,000 square km, including 3,600 homes and killing 24 people Fires started by arson, by lost hunter trying to signal rescuers

23. Case in Point Firestorms Threaten a Major City: Southern California Firestorms, 2003 and 2007 Some died after ignoring evacuation orders Neighborhoods were closely spaced wood houses surrounded by pine trees Four years of drought had left trees vulnerable to bark beetle infestation, which killed many trees Insured losses from fires topped $1.25 billion Rainy, snowy weather stopped spread of fire, but caused mudslides, killing 15 people

24. Case in Point Firestorms Threaten a Major City: Southern California Firestorms, 2003 and 2007 Mediterranean climate gets 90% of its rain in winter and early spring Chaparral or scrub brush covers hillsides Hydrophobic soils promote runoff and erosion

25. Case in Point Firestorms Threaten a Major City: Southern California Firestorms, 2003 and 2007 Exactly four years later, catastrophic fires ignited in same areas by Santa Ana winds Firefighters fought until forced to retreat by tall flames Winds died down after four days 2,000 square km burned, more than 800,000 people were evacuated, more than 2,300 homes and businesses destroyed, more than $1 billion in damages, seven people killed Even more people rebuilt in burned areas, with larger homes

26. Case in Point A Major Wildfire after Years of Fire Suppression: Bitterroot Valley Fires, Montana, 2000 Lightning led to five major fires, then 78 new fires – some merged into giant forest fire complexes 70 homes, 94 vehicles lost and more than 1,500 people evacuated Vigorous fire suppression of past years had doubled percentage of fire-vulnerable trees Several large fires remained uncontrolled from June to September About 10,000 firefighters and support people worked on fires Population had increased 40% from 1990 to 1998, with many building in unsuitable sites