1 / 53

Lecture Outlines Natural Disasters, 7 th edition

Lecture Outlines Natural Disasters, 7 th edition Patrick L. Abbott Fire Natural Disasters, 7 th edition, Chapter 15 Fire Used by humans for hundreds of thousands of years Allowed migration into colder climates Diverse successful civilizations Increased number and quality of foods

Download Presentation

Lecture Outlines Natural Disasters, 7 th edition

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Lecture OutlinesNatural Disasters, 7th edition Patrick L. Abbott

  2. FireNatural Disasters, 7th edition, Chapter 15

  3. Fire • Used by humans for hundreds of thousands of years • Allowed migrationinto colder climates • Diverse successfulcivilizations • Increased number and quality of foods • Aid inhuntingand inagriculture • Hardeningproperties  pottery, weapons, etc.  smelting, metals • Sterilization public health • Controlled inside machinery provides energy for civilization industry, domestic power, travel

  4. Fire • Destructive powers of fire: • Destruction of enemies – obliteration of Troy • Denying enemies their prize – scorched earth policy • Bombs creating firestorms in World War II • Natural world • 1,800 thunderstorms active on Earth each hour • Lightning starts 15% of U.S. fires • Most fires started by humans

  5. What is Fire? • Rapid combination of oxygen with carbon, hydrogen, and other elements of organic nature in reaction that produces flame, heat and light • Fire reaction: • C6H12O6 + 6 O2  6 CO2 + 6 H2O + released heat • Is reverse of photosynthesis reaction: • 6 CO2 + 6 H2O + heat from Sun  C6H12O6 + 6 O2 • Solar energy stored by plants during growth is returned to atmosphere during fire

  6. The Need for Fire • Organic material produced by plants is recycled by slow decomposition and rapid burning • Decomposition requires heat and moisture efficient in humid climates • Sparse vegetation of deserts  little material to decompose • Mediterranean climates: • Wet winters too cold for decomposition to occur efficiently, but still produce abundant vegetation • Fire (during dry summers) necessary for recycling of plant material, release of stored chemical potential energy • Necessary for health of some plant communities: germinates seeds, controls parasites, influences insect behavior

  7. The Burning of Rome, 64 C.E. • Fire broke out in Circus Maximus and spread to cramped neighborhoods (Emperor Nero returned from Antium to Rome) • Six days: fire spread through 10 of 14 districts • Nero played lyre and sang own composition “The Fall of Troy” while fire raged • After fire, Nero rebuilt Circus Maximus and other areas, paid to remove debris, ordered safe reconstruction measures (wider streets, stone buildings, etc.)

  8. The Fire Triangle • Fire may begin only when fuel, oxygen and heat are present in the right combination • Oxygen is 21% of atmosphere  steady supply of air • Heat warms up and dries out vegetation • Fire mostly limited by amount of fuel available Figure 15.2

  9. The Fire Triangle • Any combustible material can be fuel (organic or human-made): grasses, shrubs, trees, slash (organic debris left on ground after logging or storms), houses • Understoryof slash and shrubs ladder fuelallows fire to spread up into tall trees  major wildfires Figure 15.5

  10. The Fire Triangle • Firefighting: • Waterreduces heat • Reddish-orange viscous fluidsblock oxygen from plants • Bulldozing vegetation or setting backfiresremoves fuel Figure 15.3

  11. An Ancient View of Fire Aristotle’s synthesis in 4th century B.C.E.: all matter composed of varying proportions of four elements, each with varying qualities of hot and cold, wet and dry • Air: hotness and wetness • Earth: coldness and dryness • Fire: hotness and dryness • Water: coldness and wetness Figure 15.4

  12. The Stages of Fire • Preheating: water expelled from fuel by nearby flames, drought, hot summer day • Wood needs to be dry and hot to burn • Cellulose is stable up to 250oC, breaks down quickly at 325oC • Cellulose begins to degrade duringpyrolysis • Chemical structure breaks apart, yielding flammable hydrocarbon vapors, water vapor, tar, mineral residues • If oxygen present, temperature raised  pyrolized gases ignite  combustion begins Figure 15.6

  13. The Stages of Fire • Flaming combustion: stage of greatest energy release, through convection, radiation, conduction, diffusion, as gases released by pyrolysis combustion • Glowing combustion: wood itself burns slowly, at lower temperature, without flames (oxidation) Figure 15.8

  14. The Spread of Fire • Wildfire styles: • Move slowly along ground mostly by glowing combustion • Wall of fire with flaming combustion front • Race through treetops as crown fire • Depends on: • Types of fuel • Weather and strength of winds • Topography of land • Behavior within fire itself

  15. The Spread of Fire Figure 15.9

  16. The Spread of Fire Figure 15.9

  17. The Spread of Fire Figure 15.9

  18. The Spread of Fire Figure 15.9

  19. The Spread of Fire Fuel • Energy release depends on chemical composition of plants and organic debris • Eucalyptus: high oil content, ignites easily, burns very hot Wind • Continuous supply of fresh oxygen • Distributes heat • Pushes flames forward • Transports flaming debris to start new fires

  20. The Spread of Fire Topography • Microclimates of different plant communities • Turbulence of winds blowing through rugged topography • Steep canyon slopes have high levels of radiant heat • Fire burns faster upslope than downslope – rising heat preheats slope above and creates chimney effect Figure 15.10

  21. The Spread of Fire Fire Behavior • Heat given off creates unstable air and convection columns  fire tornadoes Figure 15.11

  22. The Fuels of Fire Grasses • Cover much of prairies of central U.S. and Canada • Late summer, early fall: dry grasses ignite easily, lightweight fuels • Fast, tall grass fires can kill and destroy property Shrubs • Loose layering allows easy burning • High content of natural oils (palmetto, snowberry, chaparral) promote fires • Florida: 1998 wildfires after warm weather, heavy rainfall, excess plant growth, record-breaking drought, lightning without rain • California: scarce rain reduces plant growth except chaparral (rich in flammable oil) and inhibits decomposition chaparral plants respond by “sprouting” or “seeding”

  23. The Fuels of Fire Forests • Affected by amount of slash on ground beneath • Scarce litter: fires pass through quickly, little harm to trees • Abundant, dry litter: fires kill trees by burning hot and slow, or slash is ladder to treetops, becomes crown fire Figure 15.16

  24. Fire Weather • Fire hazards greatest where biggest differences between wet and dry seasons • Rainy season promotes plant growth • Dry season or drought dehydrates living and dead plants  easier to burn • Dry, windy patterns affect large region  major fires break out in bunches • More than 95% of burned area caused by 2-3% of fires

  25. Winds of Fire • Large-scale movements of air-mass fronts • Small-scale local winds (temperature and topography differences) Cold-front Winds • Cold fronts move at 30 to 50 km/hr with gusty conditions for hours • Dry in summer Foehn Winds • High-pressure air mass spills over mountain range at up to 160 km/hr and descends as warm, dry wind toward low-pressure zone – caused by pressure gradient, warms adiabatically

  26. Winds of Fire Foehn Winds • Occur in September through April in western U.S. when high-pressure air sits over Great Basin and Rocky Mountains • Different names for foehn winds in different places Figure 15.17

  27. Fire Weather • Local Winds • Sea breezes, land breezes: temperature differences between land and ocean surfaces • Slope winds, valley winds: temperature differences between valley and ridge Figure 15.19

  28. Fire Weather Great Lakes Region • Late 1800s: heavy logging left abundant slash, farmers used fire to clear land for agriculture • 1871: summer, early autumn drought followed by strong winds blew farmers’ small fires out of control Peshtigo, Wisconsin: deadliest forest fire in U.S. history • 24 km widecrown fireraced forward with fire tornadoes • Covered 65 km and killed 1,152 people Chicago, Illinois: fire broke out in O’Leary’s barn • Spread northeast through flammable businesses to river • Jumped Chicago River to burn tenements and spread downtown • In 27 hours: burned most of downtown, 300 people killed (O’Leary’s house undamaged)

  29. Fire Weather • Four seasons: flood, drought, fire and earthquake • Winter rains send plants into fast-growth mode • Months of heat and drought kill and dehydrate plants Oakland and Berkeley Hills (1991) • Expensive homes and decorative plants • Late 1980s five-year drought dried plants • 1990 freeze killed more plants • 1991 rainy spring spurred rapid grass growth • Rest of 1991 drought killed grasses • Dangerously high volume of dead and dry vegetation

  30. Fire Weather Oakland and Berkeley Hills (1991) • October 19: fire of suspicious origin started near hilltop • Fire extinguished Saturday evening • Planned return Sunday morning to control smoldering duff • Sunday morning Diablo winds blew sparks from duff into crown fire, blown in changing directions • October 20: fire burned out of control • Flames reached 1,000oC  firestorm • Consumed 790 homes in one hour • Continued all day throughout Oakland and Berkeley Hills, until early evening winds changed direction

  31. Fire Weather • Oakland and Berkeley Hills (1991) • Never reached much more densely populated flatlands – desperate evacuation plans in place but not implemented • 25 people killed, about 3,000 dwellings destroyed, $1.5 billion in damages Figure 15.20

  32. Fire Weather Southern California • Long dry season, chaparral vegetation, foehn winds • October 27, 1993: Santa Ana winds spread fires from downed power lines, transient’s campfire, arsonists’ fires • October 29: Winds died down, some control gained Figure 15.23 • November 2: • Winds hit up to 80 km/hr • Fires burned out of control, stopped only at ocean • Firestorms spun off tornadoes, starting new blazes • 3 people killed, 1,150 homes destroyed, $1 billion in damages, 215,000 acres burned

  33. Home Design and Fire • Poor decisions: • Home of wood or roofed with wooden shake shingles • Wooden decks extending over steep slopes (concentrate heat) • Natural or planted vegetation from yard right up to house or draping over roof • House can ignite by: • Flames traveling through vegetation or along wooden fence • Flames generating enough radiant heat to ignite exterior • Firebrands carried by wind dropped on or next to house

  34. Home Design and Fire Figure 15.26

  35. Home Design and Fire • Safer decisions: • Clay- or concrete-tile roofs, stucco exterior walls, double-pane windows, few overhanging roofs or decks Figure 15.28

  36. Home Design and Fire • Safer decisions: • Fire breaks of cleared vegetation extending at least 9 m from house, farther if on a slope Figure 15.29

  37. Home Design and Fire

  38. Home Design and Fire How Well Have Californians Learned? • 1923: firestorm destroyed 584 houses in Oakland, Berkeley Hills • Committee identified six factors that led to building loss • After 2003 San Diego wildfires, task force identified six factors that led to building loss • Five of six factors are identical on two lists

  39. Fire Weather: The Winds of Madness Santa Ana winds of southern California • Push firestorms • Affect people’s moods and behaviors • High wind speeds, extra low humidity, electrically charged air with 7 to 9 times normal level of positive ions • Described as ‘winds of madness’ • Increases in domestic violence, household mishaps, allergic reactions, migraine headaches, suicides

  40. Fire Suppression • 1910 Big Blowup: over 3 million acres in Idaho and Montana burned, destroying towns and killing 85 people • Forests with 30 big trees per acre  typical ground fires burnt grasses and thin litter without harming trees • Congress appropriated federal money to fight forest fires  policy of suppressing forest fires with professional fire fighters • 20th century fire suppression tactics and equipment improved  dramatic reductions in number of acres burned • After limiting fires, forests have 300 – 3,000 big trees per acre and shrub understory  slow, hot fires kill big trees

  41. Fire Suppression

  42. Fire Suppression Yellowstone National Park • Oldest national park, about 15 lightning fires per year • Policy from 1880s to 1970s: • Extinguish all fires as soon as possible • Shift in 1970s to natural management changed policy to: • Extinguish human-made fires, let lightning fires burn • Between 1976-1987: 235 lightning fires, about 100 acres each • Policy judged successful • Winter of 1987-88 was dry • Many trees had been killed by mountain pine beetles • 90 years of fire suppression built up dead wood on ground • Moisture levels in wood dropped from 15-20% to 2-7%

  43. Fire Suppression Yellowstone National Park • Summer of 1988: • Lightning fires began as usual • Not followed by usual June-July rains • By late July, over 17,000 acres had burned • New policy enacted to extinguish all fires • High temperatures and high winds of August allowed fires to burn out of control until mid-September snows weakened them, then November winter conditions extinguished fires

  44. Fire Suppression • At fire’s conclusion: 1.4 million acres burned, almost half of Yellowstone • In previous 116 years, only 146,000 acres burned • Ten years later: • Opened land to increased sunlight and nutrients  grasses, wildflowers, shrubs, tree seedlings, enriched soil Figure 15.31

  45. Fire Suppression California vs. Baja California: Pay Now or Pay Later • Long-term effect of short-term fire suppression: in U.S., fires fought energetically and expensively, to not let fire interfere with human activities • Chaparral allowed to grow older, more flammable • Hot, dry Santa Ana winds unleash unstoppable firestorms • Fewer fires, but more large ones • In Baja California, Mexico: fires allowed to burn with little or no interference • Older chaparral surrounded by younger, less-flammable plants • More numerous fires, but smaller

  46. Fire Suppression • Between 1972-80, percentage of chaparral acreage burned in U.S. and Mexico was about the same

  47. Fire Suppression • U.S. fire-fighting reduced number of fires, not acreage burned • Santa Ana firestorms burn huge areas, kill people, destroy thousands of buildings Figure 15.33

  48. Fire Suppression The Cedar Fire in San Diego County, October 2003 • Huge areas of old chaparral fuel, dried by five years of drought • Lost hunter started signal fire, flames pushed westward by Santa Ana winds  burned 282,000 acres, destroyed 2,232 buildings, killed 15 people • Fire stopped when it encountered areas recently burned in 2001 Viejas fire and 2001, 2002 and 2003 prescribed Tragedy burns  would have burned more than 400,000 acres otherwise

  49. Fire Suppression The Western and Southern United States in 2000 • Fires in 2000 burned almost three times more acreage than average year, with 20% more fires • On busiest day: • 84 large fires on 1.6 million acres in 16 states • Cool La Nina ocean water in eastern Pacific in 1999, 2000  drier than average weather in southern states

  50. Fire Suppression Prescribed Fires • Solution to problem of dense forests and shrublands: deliberately set prescribed fires at times of low wind speeds, low temperatures, high humidity, good soil moisture, approaching rain, etc. • 1995 to 2000: more than 31,000 prescribed fires Los Alamos, New Mexico, May 2000 • Controlled fire set at Bandelier National Monument to clear understory of brush • Following day, high winds blew prescribed fire into wildfire: • Consumed 50,000 acres of national forest, 235 Los Alamos houses, 115 buildings at Los Alamos National Laboratory, close to nuclear weapons research facility

More Related