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Natural Hazards Wildfires Chapter 13 Learning Objectives Understand wildfire as a natural process that becomes a hazard when people live in or near wildlands Understand the effects of fires Know how wildfires are linked to other natural hazards Know potential benefits provided by wildfires Learning Objectives, cont. Know the methods employed to minimize fire hazard Know potential adjustments to wildfire hazard Introduction to Wildfire Before humans, fires would burn until they ran out of fuel naturally. Fire initiates new plant growth and clears out dead matter. Humans introduced “slash and burn” technology for farming, which made weak soils even worse. Fire is still used in many places, including the United States, to prepare soil for farming. Wildfire as a Process Self-sustaining, rapid, high temperature biochemical reaction Requires Fuel Oxygen Heat Inserting water into this model helps stop or prevent fire by blocking fuel from “oxidizing”. water Three Wildfire Phases: Preignition Fuel achieves temperature and low humidity favorable to ignition. Preheating Fuel loses water and other chemical compounds Pyrolysis Processes that chemically convert hydrocarbons into fuel Products include volatile gases, mineral ash, tars, etc. Three Wildfire Phases: Combustion Begins with ignition – self-sustaining combustion. External reactions liberate heat and light. Lightning, volcanic activity, and human action. Ignition doesn’t always lead to wildfires. Pre-ignition absorbs energy, combustion releases energy. Sufficient fuel must be present, dry enough as well. Ignition is not a single process but occurs repeatedly as wildfire moves: drying igniting combusting more drying. Wildfire Phases: Flaming combustion Dominates early fire Rapid high temperature conversion of fuel into heat heat is needed to dry and ignite more fuel. Characterized by flames and large amount of unburned material Smoldering combustion Takes place at lower temperatures Large amounts of fuel not fully combusted. The key is conversion of hydro-carbon (organic) material into fuel combustion -- the result is conversion of organics into in-organic minerals. Exhaustion of fuel results in decline of fire. How does this process compare to an ordinary thunderstorm? Heat, buoyancy, rising air, low atmospheric pressure, water vapor released from organic material. Convective rising of humid, hot air Convection in Wildfires Transfer occurs as convection and radiation. Radiation heat increases surface temperature of fuel. Hot gases are less dense, especially with liquid water converted into vapor - - rising air. Rising vapor can convert back to liquid with cooling altitude. Rising air pulls in fresh air to sustain combustion. Heat transfer by radiation can be enough to start the combustion process. Three Wildfire Processes: Extinction Point at which combustion ceases. There is no longer heat and fuel to sustain fire. Fire Environment: Fuel Leaves, twigs, decaying organic material, grass, shrubs, etc. Peat–Unconsolidated deposit of partially decayed wood, leaves, or moss. Landslides, hurricanes, and tornadoes can arrange debris to facilitate fires. Organic materials can dry out during droughts to become fuel – or be dried-out by heat-related pests (pine beetle). Fire Environment Fuel moisture content is affected by weather and slope exposure. Drier fuels are found: On south-facing slopes in Northern Hemisphere Slopes exposed to prevailing winds Mountainous areas circulate winds up canyons during daytime. Wildfires pre-heat fuels upslope, making it easier to spread. Wild Fire Environment: Weather Wild fires are common following droughts. Can bring “dry thunderstorms” with lightning to start fires, but rain evaporates and can’t extinguish them Fires burn more when humidity is lowest. What happens to fire conditions: At night? During the day? <Humidity goes UP at night when air temperature is lower> Salt Lake billboards say that burning embers can travel up to a mile. Wind direction and strength help preheat and pre-dry unburned materials. Winds carry embers to ignite spot fires ahead of front. Types of Fires: Ground Fires Creep along under ground surface Little flaming, more smoldering Surface Fires Move along surface Clears-out dead wood, duff, debris May preserve trees and improve habitat and watershed. Types of Fires: Crown Fires Flame is carried via tree canopies. Driven by strong winds and steep slopes. Can destroy the entire forest Crown Fires can be compared to other ‘conflagrations’ and ‘fire storms’ Wind speeds can rival aerial bombing and even atomic weapons. <Dresden, Tokyo, Hiroshima, Liverpool> Crown Fires (and conflagrations, infernos, fire storms) How is this any different from a tornado or hurricane? The internal convective process creates an everlarger fire until fuel is exhausted. This is a “positive” cycle in which more leads to more until fuel runs out. <both accelerate with additional “fuel”> Severe weather relies on energy in humidity Severe fires require hydrocarbon fuel. In fact, whirlwinds or vortices of spiral-rising air are sometimes seen in the most severe wildfires. As flames heat the air, evaporation occurs, drawing lighter, more buoyant air aloft, encouraging yet more in-flow of surface oxygen for combustion. Western states experience more wild fires There is a correlation between wildfires and dry climates? Dry country may grow less ‘fuel’ but the fuel ignites more easily. How is this hazard related to climate change? Western USA Effects of Wildfires on Geologic Environment Soil changes Water-repellent hydrophobic layer – water “beads off” instead of being absorbed. Increases runoff and erosion and flood events Soil erosion and landslides Removal of anchoring vegetation on steep slopes Precipitation often exaggerates the effect of fires on landslides Wildfires cause air pollution and rain Fire heat evaporates water in plants and soil. Hot, humid air rises decompresses cools condenses and then precipitates that water back to earth. The 2007 Utah Neola fire exhibited daily cumulo-nimbus clouds overhead as evaporated water condensed and rained back to earth each afternoon. Smoke, soot, and gases contribute to pollution. Ground-level ozone may result from oxide gases combining with solar rays. Linkages of Wildfires with Climate Change Climate change increases intensity and frequency of wildfires. Caused by changes in temperature, precipitation, and the frequency and intensity of severe storms. Increases in temperature, decreases in humidity. <drying> Lightning strikes cause ignitions. North America is infested with ‘pine beetles’ that persist more easily with warming atmosphere. Once again, the 2007 Utah Neola fire is a good example – firefighters finally gave up – “Kill ‘em all” <they said> Effects of Wildfires on Biological Environment Vegetation Animals Fire can destroy some vegetation. Weakens others. Some plants use fire to propagate. Most animals may flee unharmed. Habitats are altered, often for the better in the long run. Humans Water quality is affected. Smoke and haze produce eye, respiratory, and skin problems. Destroys personal property. Natural Service Function of Wildfires Reduce populations of microorganisms Benefits to plants and animals Reduces the number of species of plants May trigger a release of seeds in some species Removes surface litter for grasses Recycles nutrients in system – mineral ashes become plant nutrients Animals move more easily More precipitation is absorbed by the soil rather than evaporated Minimizing the Wildfire Hazard Science – learning more about the role of fire in a healthy world ecosystem Education and regulation – are people the real problem? Policy and Practice – Is “Smokey the Bear” right – or wrong? Does it really depend on the situation? Meanwhile, is there a better way to keep state and federal agencies funded without having to earn revenue by filling the wild with buildings and people who need rescue? People do not adequately perceive risk of wildfires. People make demands on government for suppression. Insurance may give people a false sense of security. Millions of buildings now exist in fire-prone wild land. Burning buildings create very toxic fumes from synthetic materials, such as plastics that contain chlorine, cadmium, etc. Minimizing the Wildfire Hazard Mapping and data collection Prescribed burns Controlled burns to manage forests Reduces fuel to prevent more catastrophic fires Utah’s Governor became quite angry in 2012 when a prescribed burn got out of control and consumed several expensive homes in Southern Utah. Fourteen Utah homes were burned in 2013 due to wildfire. Mr. Allred managed a State of Utah research project into machinery for conversion of cellulosic forest waste into methanol vehicle fuel. Using that methanol for vehicles that collect and process more forest waste is a self-sustaining process that produces little pollution. Grooming forests to prevent periodic fires is better than allowing fires that may get out of control, create air pollution and endanger people and property. Unfortunately, turning forest waste into methanol fuel is more difficult than making ethanol fuel with corn.