2019_KittitasCountyHMP_Volume 1_For Adoption

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15-1 CHAPTER 15. WILDFIRE 15.1. GENERAL BACKGROUND The wildfire season in Washington usually begins in early July and ends with precipitation in late September, but wildfires have occurred in every month of the year. Drought, snow pack, and local weather conditions can affect the length of the fire season. How a fire behaves primarily depends on the following: • Fuel—Lighter fuels such as grasses, leaves and needles quickly expel moisture and burn rapidly, while heavier fuels such as tree branches, logs and trunks take longer to warm and ignite. Snags and trees that are diseased, dying, or dead present special hazards. In 2002, about 1.8 million acres of the state’s 21 million acres of forestland contained trees killed or defoliated by forest insects and diseases. • Weather—Strong, dry winds in late summer and early fall produce extreme fire conditions. Wind events can persist up to 48 hours, with wind speed reaching 60 miles per hour; these winds generally reach peak velocities during the night and early morning. • Thunderstorm activity—The thunderstorm season typically begins in June with wet storms, and turns dry with little or no precipitation reaching the ground as the season progresses into July and August. • Terrain—Topography influences the amount and moisture of fuel; the impact of weather conditions; barriers to fire spread, such as highways and lakes; and land elevation and slope. Fire spreads uphill more easily than downhill, and the steeper the slope, the faster the fire travels. Fires travel in the direction of the ambient wind, which usually flows uphill. A wildfire is also able to preheat the fuel further up the hill because the smoke and heat are rising in that direction which, in turn, increases the fire’s speed. • Time of Day—A fire’s peak burning period generally is between 1 p.m. and 6 p.m. People start most wildfires through arson, recreational fires that get out of control, smoker carelessness, debris burning, or children playing with fire. From 2001 to 2017, humans have caused 196,335 fires and lightning has caused 1,441 fires in the Northwest according to the National Interagency Fire Center. Throughout the US, on average, people caused more than 61,952 wildfires each •DEFINITIONS •Conflagration—A fire that grows beyond its original source area to engulf adjoining regions. Wind, extremely dry or hazardous weather conditions, excessive fuel buildup and explosions are usually the elements behind a wildfire conflagration. •Firestorm—A fire that expands to cover a large area, often more than a square mile. A firestorm usually occurs when many individual fires grow together into one. The involved area becomes so hot that all combustible materials ignite, even if they are not exposed to direct flame. Temperatures may exceed 1000°C. Hot gases rise over the fire zone, drawing winds in from all sides at velocities as high as 50 miles per hour. Firestorms seldom spread because of the inward direction of the winds, but there is no known way of stopping them. Within the area of the fire, lethal concentrations of carbon monoxide are present; combined with the intense heat, this poses a serious life threat to responding fire forces. In very large events, the rising column of heated air and combustion gases carries enough particulate matter into the upper atmosphere to cause cloud nucleation, creating a locally intense thunderstorm and the hazard of lightning strikes. •Interface Area—An area susceptible to wildfires and where wildland vegetation and urban or suburban development occur together. An example would be smaller urban areas and dispersed rural housing in forested areas. •Wildfire—Fires that result in uncontrolled destruction of forests, brush, field crops, grasslands, and real and personal property in non-urban areas. Because of their distance from firefighting resources, they can be difficult to contain and can cause a great deal of destruction.