LarryNanceWildfire
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The three principal environmental factors that affect wildland fire behavior are fuel, weather, and topography. The document discusses how each of these factors—particularly weather factors like relative humidity, wind speed, drought conditions, and thunderstorms—can significantly impact wildfire behavior and intensity. It provides data on past wildfire statistics in different regions and explains extreme fire behavior indicators like low relative humidity, high winds, and dry fuel conditions.
LarryNanceWildfire
- 3. QUIZ – 3 principal environmental factors that affect wildland fire behavior?
- 4. ENVIRONMENTAL FACTORS AFFECTING WILDFIRES FUEL WEATHER TOPOGRAPHY
- 7. Fires by Month 1932 - 2011 700 600 500 400 Fires 300 200 100 0 Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
- 8. Tom Foti /Susan Glenn
- 10. Oct- Dec Number of Fires by Year Fires 8000 Feb-Apr Spr- Sum 7000 6000 5000 4000 3000 2000 1000 0
- 11. June- August 2012 • 2,033 fires • 51,747 acres Other comparisons: Jan- March 1942 •3,586 fires/118,610 ac. July-Sept. 1980 •2,768 fires/73,070 ac.
- 12. Fires Larger Than 100 Acres #Acres County Date 537 Miller June 23 142 Franklin June 29 160 #Acres Clark County June 29 Date 400 104 Clark Lafayette June 29 July 19 110 109 Conway Faulkner June330 July 115 110 Hot Spring Conway July 1 June 30 250 115 Clark Hot Spring July 1 1 July 115 293 Dallas Logan July 4 1 July 116 Independence July 28 109 Faulkner July 3 140 White July 3 140 White July 3 142 Franklin June 29 471 160 Pope Clark July 3 June 29 115 179 Dallas Ashley August 4 July 3 116 199 Clark Independence July4 July 22 200 200 Dallas Dallas July 4 4 July 200 250 Benton Carroll August 4 July 7 232 Sharp August 15 104 Lafayette July 19 250 Clark July 1 199 Independence July 22 250 Carroll July 4 1,014 274 Yell Hot Spring July 25 July 30 116 o293 Independence Logan July128 July 355 300 Garland Van Buren August 29 July 28 355 274 Garland Hot Spring July 29 July 30 400 380 Clark Benton June 292 Aug. 471 Pope July 3 179 Ashley Aug. 3 537 Miller June 23 825 825 PerryPerry Aug. 13 August 13 852 852 Clark Clark Aug. 13 August 13 1,410 1,014 Drew Yell Aug. 14 July 25 232 1,410 SharpDrew Aug. 15 August 14 300 Van Buren Aug. 28
- 13. Fires by Cause (AVG) 1992 - 2011 800 700 600 500 400 Fires 300 200 100 0 Inc Debris Smokers Railroad Campfire Equip Children Lightning Misc
- 15. Extreme Fire Behavior Conditions
- 16. Extreme Fire Behavior Conditions: •Relative humidity is below 20% •Wind speeds above 20 mph •Dispersion Index value of 80+ •Haines Index - 6 •KBDI - 700-800 •Fine fuel moisture below 5% •Dust devils/fire whirls •Spotting in several directions •Thunderstorm on the horizon
- 17. Relative humidity ≤ 20%
- 18. Wind Information 20 foot winds- ≥20 mph Winds at 20 feet above the ground or 20 feet above the average height of vegetation are used in the routine fire weather forecast.
- 19. Dispersion Index ADI Description Poor dispersion, stagnant air if conditions 0-20 persist. Poor to fair dispersion, stagnation possible 21-40 with low wind speeds. 41-60 Generally good dispersion. Very good dispersion, control problems 61-80 likely. Excellent dispersion, control problems 80 + expected.
- 20. Keetch-Byram Drought Index 0-200 Soil moisture and large class fuel moistures are high and do not contribute much to fire intensity. Typical of spring dormant season following winter precipitation. 200-400 Typical of late spring, early growing season. Lower litter and duff layers are drying and beginning to contribute to fire intensity. 400-600 Typical of late summer, early fall. Lower litter and duff layers actively contribute to fire intensity and will burn actively. 600-800 Often associated with more severe drought with increased wildfire occurrence. Intense, deep burning fires with significant downwind spotting can be expected. Live fuels can also be expected to burn actively at these levels.
- 23. Thunderstorm Winds Strong and shifting winds. Speeds often greater than 30 mph result in erratic fire behavior. Wind speeds often enhanced by the forward movement of the storm. Outflow typically precedes rain by 3-5 miles, but can be much more.
- 24. Red Flag Warning Criteria • Afternoon minimum relative humidity expected to be 25% or lower. • 20 foot sustained winds in excess of 14 mph. • Fuels that are determined to be critically dry (less than 10 percent for 10 hour fuels). • Other parameters that are considered include the likelihood of lightning occurrence, wind shifts, and/or current wildfire activity.
- 25. On site Weather Observations… Kestrel Belt Weather Kit
Editor's Notes
- #3: Thanks God for Hurricane Isaac which entered Arkansas on August 30.
- #4: Prescribed Fire School question.Fire occurred on May 23 near Brewer community in Cleburne County- GBP tract.
- #6: Fire occurred on May 28 near Jerusalem in Conway County. GBP and AFC had 5 dozers on the fire. The fire burned 97 acres mostly a 7 year old pine plantation.
- #8: I was surprised by October through December. 1989 we had 761 fires in November and 804 in December.March is higher because
- #9: Lightning was a problem this summer. Lightning fires caused 25% of the fires in June and July. In August 42% of the fires were by lightning.
- #10: Casa Fire (Fire # 277) in Perry County that burned 820 acres on August 13. AFC air attack was looking at some other fires when they spotted a small 3-5 acre fire in a cut over. There was a smaller fire north of the Casa fire that was also a lightning strike- Mary Lane fire.
- #11: AFC has fire records going back to 1935 with number of fires and number of acres burned by month. We thought this year was bad. 1952 we had fires 7,326 fires. 1963 we had 5,702 fires. 1980 has blue arrow had 6,128 fires.
- #15: Little Rock National Weather Service provides Fire Weather information at 7:30 am and 3:30 pm.
- #16: There are certain factors that warn of extreme fire behavior conditions. This is the Ola fire that occurred on July 25, 2012. This fire burned 1,014 acres. This picture was taken by Doug Cloud with Tysons.
- #18: Generally getting into August we will see RH’s get down to 20%. This summer we had RH get down to 9%.
- #19: This is the prevailing wind speed in miles per hour at the level of 20 feet above vegetative cover. Eye level winds are about half.
- #20: The Dispersion Index is a numerical indicator of how well and how rapidly smoke will be dispersed. It utilizes stability, mixing height, and transport wind as the major factors. Other factors are: the amount and angle of sunlight and temperature.
- #21: The Keetch-Byram drought index (KBDI) is a continuous reference scale for estimating the dryness of the soil and duff layers. The index increases for each day without rain (the amount of increase depends on the daily high temperature) and decreases when it rains. The scale ranges from 0 (no moisture deficit) to 800. The range of the index is determined by assuming that there is 8 inches of moisture in a saturated soil that is readily available to the vegetation.For different soil types, the depth of soil required to hold 8 inches of moisture varies (loam=30", clay=25" and sand=80"). A prolonged drought (high KBDI) influences fire intensity largely because more fuel is available for combustion (i.e. fuels have a lower moisture content). In addition, the drying of organic material in the soil can lead to increased difficulty in fire suppression.High values of the KBDI are an indication that conditions are favorable for the occurrence and spread of wildfires, but drought is not by itself a prerequisite for wildfires. Other weather factors, such as wind, temperature, relative humidity and atmospheric stability, play a major role in determining the actual fire danger. KBDI for the Drew County 1,410 acre fire on August 14 was 759.
- #22: The amount of moisture in fuel is the major element that will determine how much of the fuel will burn (available fuel). According to how much moisture is in the fuel, all will burn, only part will burn or, if wet enough, none will burn. Fuel moisture values down to 3% with temperatures of 95 degrees plus. Probability of ignition was 80% or greater.