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Natural hazards wildfires

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  • 1. WildfiresDavid AlexanderUniversity College London
  • 2. Forest and rangeland fires (wildfires)are a source of importantecological and economic damage andrisk to human lives and settlements.A wildfire burns out of control andthreatens people, buildings or resources.
  • 3. Synonyms:-• bushfire (Australia)• forest fire, range fire (North America)• environmental fire• wildfire.
  • 4. Phases of wildfire:-• confined - limited to apredetermined area usingnatural and man-made barriers• contained - surrounded by a controlline so that it cannot spread further• under control - completelyencircled by the control lineand burning in predictable ways.
  • 5. The causes of wildfires:-• lightning strikes (a naturalcause of varied importance)• human negligence and vandalism(greatest at theurban-rural interface)• vegetative fermentation leading tospontaneous combustion are possiblebut not probable causes of wildfires.
  • 6. Dendrochronology: the frequency ofwildfires in the past is visible in damageto the xylem of the tree, which can bedated by counting the annual rings.
  • 7. Model of the acceleration of a wildfirein an open environmentTime (minutes)Proportionofareaburnt
  • 8. Map of the evolution of a wildfire in the USA
  • 9. AreainvolvedMaximumspread of firePeak offireDying outDying outExtinctFlashoverLatentStartof fireAccele-rateddiffusionMainfirephaseTimeEmission ofsmoke andhot gasesBeginning
  • 10. The dimensions, duration and intensityof wildfires varies according to:-• the type, inflammability and watercontent of wood: the loading factorfor combustible material• meteorological conditions(temperature, humidity)• the speed, direction andvariability of winds• topography and groundslope in the local area.
  • 11. The essential ingredientsof a wildfire are:-• combustible material• heat• oxygen.
  • 12. Classification of wildfires:-• ground fire: combustion without flamesin the roots and undergrowth• surface fire: in rangelands,undergrowth, etc.• spot fire: localised, concentrated• dependent crown fire: the crowns oftrees catch fire but the fire ispropagated in the undergrowth.
  • 13. (a) Ground fire (c) Dependent crown fire(d) Running crown fire(b) Surface fire
  • 14. More elements of the classification:-• running crown fire: the fire ispropagated through the tree crowns• a “backfire” can occur if thewind changes direction and thecombustible material has notbeen completely consumedA wildfire can climb a slopepropelled by wind convectionand by heat radiation.
  • 15. Convective wildfire which climbsa slope propelled by wind turbulence
  • 16. Convective wildfire that climbs a slope
  • 17. Ground fire
  • 18. Running crown fire
  • 19. Wildfire fuel can be classified as:-• aerial material: branches, leaves, moss• surface material:low-level vegetation, wood,leaves, grass, detached branches• buried and composting materials• mineral soil and roots.
  • 20. Some environmental effectsof wildfires:-.... on vegetation:• can stimulate the growthof rangelands and meadows• can encourage the germination of seeds• can stimulate floweringof bushes and plants• but can restrict thegrowth of woody plants.
  • 21. .... on soil:• they can purify soil by destroyingtoxins, fungi and parasites• but can accelerate erosion of the soil.... on birds:• can destroy nests and causefragmentation of habitatsEcological environments createdor maintained by wildfire showthe greatest diversity of species.Environmental effects of wildfires:-
  • 22. Australia has an extremely high wildfirerisk: 40% of the nation contains adequatecombustible material, the climate is dry,temperatures are high and damagingfires are common.
  • 23. Mediterranean maquis (chaparral inCalifornia) is highly inflammableMediterranean vegetation gives rise tovery hot fires (540-1100 degrees C),fed by dry bushes that arefull of highly inflammable oils.
  • 24. The elimination of Mediterraneanvegetation by wildfire can:-• impermeabilise surfaces by depositingnatural polymers (hydrophobic residues)• cause surface slides of dry ravel• cause mudflows and debris flows• contribute to the formation of gullies.
  • 25. Mitigation of wildfire:-• controlled fire - can reduce fuelloading levels, but it remainscontroversial and can cause damage• total elimination of wildfires allowsmassive accumulations of inflammablematerial and therefore leadsto much bigger and hotterfires that spread more rapidly.
  • 26. Monitoring of wildfire risk:-• lookout towers and field patrols• aerial surveillance• infrared monitoring from theground, the air and satellites.
  • 27. INDEX OF FUEL AVAILABILITYALGORITHM USED TOCALCULATE AN INDEXOF FUEL AVAILABILITY
  • 28. Wildfire fighting:-• one needs to reduce the supply ofheat, oxygen or fuel to the fireThe attack:• train personnel• use parachute brigades in areasthat are difficult to reach• construct corridors of low fuel loading.
  • 29. The attack:• dump water or flame retardantchemicals from aircraft• Canadair CL-215 "Super Scooper"aircraft are able to take up6,000 litres of water in 12 seconds• drop water on flames from helicopters.
  • 30. Bell-412helicopterscan transport1,400 litresof water.
  • 31. C-130 aeroplanes can carry 11,000 litresof flame-retardant chemicals
  • 32. California Firescope, a centralisedsystem of fire fighting:-• an Incident Command System (ICS)• a coordination system for variousagencies that work in the field(Multi-Agency Coordinating System,MACS) -- for 28 agencies• an Operations CoordinationCenter (OCC) for field attacks.
  • 33. Average annual number of forest firesin 12 U.S. statesTotal numberCaused by lightning
  • 34. California Firescope includes an informationsystem and data bank, which covers:-• weather forecasting• infrared surveillance of areasat greatest risk of wildfires• immediate reports on the stateof fires and suppression activities• advice on the best tacticsto adopt for fighting fires.[X]

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