6/2/2023 0 Comments Steep ravines downloadBecause heat rises, the heat energy released through convection and thermal radiation rises up slopes at an increased rate of spread. Topography dramatically affects the behavior and spread of wildfire. Such climatic changes can also affect the availability of adequate water resources to fight wildfires. Since the mid-1980s, climatic warming and earlier snowmelt have been associated with an increasing length and severity of the wildfire season in the western United States. For example, years of precipitation followed by prolonged dry spells or increased temperatures can result in more widespread fires or longer fire seasons. Over time climatic changes in seasonal weather patterns can alter the distribution of vegetation and fuels as well as their susceptibility to fire ignition or spread. And it can cause an uplift and spread of burning embers at great distances from the fire, resulting in additional sources of fire ignition far from the fire’s leading edge. Wind can also accelerate the pre-heating of fuels downwind from the leading edge of fire, accelerating the rate of fire spread. Wind increases the supply of oxygen to a fire and can distort or alter the path or direction of fire. Even before the flames of a wildfire reach a particular location, the energy released through convection and thermal radiation from the wildfire’s front heats the surrounding air to 800° C, which preheats and dries flammable materials, causing them to ignite faster and accelerate the spread of fire. Significantly, wildfires often create their own weather effects by superheating the surrounding atmosphere, resulting in increased drying and combustibility of fuel sources as well as uplifting of embers and more intense winds and cross-currents. Prolonged dry spells intensify the combustibility of vegetation and other fuels, while precipitation increases humidity and can prevent fire ignition or dampen fire spread. Increased temperature combined with low humidity can result in higher combustibility of vegetation and other fuels, such as wood structures. Temperature, humidity, precipitation and wind are each important weather variables that influence the intensity and spread of fire.
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