Crown Fire Methods - National Wildfire Coordinating Group
Sharing Fire Behavior Practices and Lessons Learned November 16, 2015 Crown Fire Methods LaWen Hollingsworth Rocky Mountain Research Station Fire Modeling Institute Missoula, MT Background Two crown fire methods: Finney (1998) Scott and Reinhardt (2001) Both methods available in: WFDSS STFB, NTFB, FSPro
Stand-alone Systems FlamMap, FARSITE Model Finney (1998) Scott and Reinhardt (2001) Surface fire spread Rothermel (1972) Rothermel (1972)
Crown fire initiation Van Wagner (1977) Van Wagner (1977) Crown fire spread Rothermel (1991) Rothermel (1991) Spotting Albini (1979)
Albini (1979) Critical surface intensity Crown fire initiation model (Van Wagner 1977) 1. Canopy base height 2. Foliar moisture content Critical surface intensity = SURFACE FIRE Critical crown fire spread rate (Van Wagner 1977, modified by Alexander 1988) 1. Canopy bulk density Critical surface intensity crown fire initiation model (Van Wagner 1977) 1. Canopy base height
2. Foliar moisture content Critical crown fire spread rate (R0) ritical surface intensity = PASSIVE CROWN FIRE = ACTIVE CROWN FIR Critical crown fire spread rate (R0) ritical surface intensity Summary by Type of Fire Type of Fire Surface
Byram (1959) None Passive Surface + some crown (Finney) or Rcrown (S/R) Thomas (1963)
Yes Active Surface + some crown Rcrown Thomas (1963) Yes Crown Fire Spread Rate crown
= Rsurface + CFB ( Ractive Rsurfac Rcrown = Rsurface CFB = Ractive = actual crown fire spread rate = surface rate of spread (Rothermel 1972) crown fraction burned active crown fire spread rate (Rothermel 1991) CFB Crown Fraction Burned weighted average of surface and crown fire spread rates
proportion of trees involved in the crowning phase Scott and Reinhardt method Finney method 0 Crown Fraction Burned 1.0 Important Considerations For the analyst, holding all modeling components equal: When using Scott & Reinhardt (2001), passive crown fire spread rate can vary greatly between the surface fire spread rate and the potential crown fire spread rate,
depending on the fire environment. When using Finney (1998), passive crown fire spread rate will be the same as surface fire rate of spread. HOWEVER, passive crown fires loft embers so overall fire growth will be greater than surface fire. Spotting Spotting CC and CFB are used to calculate the number of torching trees (which influences firebrand lofting height) Crown fraction burned Canopy cover < 0.5 0.5 0.8
TorchingTrees Trees Vertical Lofting Ember Burnout Time Windspeed Profile Plume Height Transition Zone Flame Height 20-ft Windspeed
Important Considerations In STFB and NTFB in WFDSS, spotting default = 0.00% Spotting is stochastic in STFB, NTFB, and FSPro Spotting only occurs when passive or active crown fire is modeled More embers are lofted at finer landscape resolutions in STFB and FSPro For an individual fire, a larger predicted size will encounter more nodes therefore more embers are launched Same But Different laurahamilton.theworldrace.org
Same But Different SAME DIFFERENT Threshold between surface fire and some type of crown fire (critical surface intensity) Finney method lower crown fire spread rate lower crown fireline intensity lower crown flame length Proportion of surface fire versus some type of crown fire
Scott and Reinhardt Faster ROS for passive crown fire Faster ROS for active crown fire Generally speaking, Active crown fire (Finney) Active crown fire (S&R) Scott and Reinhardt Larger overall fire growth for passive crown fire Larger overall fire growth for active crown fire Selecting a Crown Fire Method
Finney method Selecting a Crown Fire Method www.reddit.com Finney method Scott and Reinhardt method Selecting a Crown Fire Method
N IO T A R B I L & E CA C N E I
R E P EX Finney method Scott and Reinhardt method References Albini, F.A. 1979. Spot fire distance from burning treesa predictive model. Gen. Tech. Rep. INT-56. Ogden, UT: USDA Forest Service, Intermountain Forest and Range Experiment Station. Alexander, M. E. 1988. Help with making crown fire hazard assessments. In: Fischer, W. C.; Arno, S. F., comps. Protecting people and homes from wildfire in the Interior West: proceedings of the Symposium and Workshop; 1988 October 6-8; Missoula, MT. Proc. Gen. Tech. Rep. INT-251. Ogden,
UT: USDA Forest Service, Intermountain Forest and Range Experimental Station. pp. 147- 156. nd Byram, G. M. 1959. Combustion of forest fuels. In: Forest fire: Control and use, 2 edition. New York, NY: McGraw-Hill: chapter 1, 61-89. Finney, M. A. 1998. FARSITE: Fire Area Simulatormodel development and evaluation. Res. Pap. RMRSRP-4. Ft. Collins, CO: USDA Forest Service, Rocky Mountain Research Station. 47 p. Finney, M.A. 2004 FARSITE: Fire Area Simulatormodel development and evaluation. Res. Pap. RMRSRP-4 Revised. Ft. Collins, CO: USDA Forest Service, Rocky Mountain Research Station. 52 p. Rothermel, R. C. 1972. A mathematical model for predicting fire spread in wildland fuels. Res. Pap. INT115. Ogden, UT: USDA Forest Service, Intermountain Forest and Range Experiment Station. 40 p. Rothermel, R. C. 1991. Predicting behavior and size of crown fires in the Northern Rocky Mountains. Res. Pap. INT-438. Ogden, UT: USDA Forest Service, Intermountain Forest and Range Experiment Station. 46 p. Scott, Joe H.; Reinhardt, Elizabeth D. 2001. Assessing crown fire potential by linking models of surface and crown fire behavior. Res. Pap. RMRS-RP-29. Fort Collins, CO: USDA Forest Service, Rocky Mountain Research Station. 59 p. Thomas, P. H. 1963. Size of flames from natural fires. In: Proceedings of the Ninth Symposium on Combustion.
1962. New York, NY: Academic Press. pp. 844-859. Van Wagner, C. E. 1977. Conditions for the start and spread of crown fire. Canadian Journal of Forest Research 7: 23-34. Questions and Comments
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