Introduction to Fire Behavior Modeling Introduction to Wildfire Behavior Modeling Introduction Table of Contents Introduction ........................................................................................................ 5 Chapter 1: Background........................................................................................ 7 What is wildfire? ..................................................................................................................... 7 Wildfire morphology ............................................................................................................. 10 By shape........................................................................................................ 10 By relative spread direction ........................................................................... 12 Wildfire behavior characteristics ........................................................................................... 14 Flame front rate of spread (ROS) ................................................................... 15 Heat per unit area (HPA) ................................................................................ 17 Fireline intensity (FLI) .................................................................................... 19 Flame size ..................................................................................................... 23 Major influences on fire behavior simulations ....................................................................... 24 Fuelbed structure .......................................................................................... 25 Fuel moisture content ................................................................................... 26 Slope characteristics ...................................................................................... 29 Wind characteristics ...................................................................................... 30 Relative spread direction ............................................................................... 30 Chapter 1 summary............................................................................................................... 33 Chapter 2: Characterizing Surface Fuel for Fire Behavior Modeling .................. 34 Fire behavior fuel models ...................................................................................................... 34 Standard fire behavior fuel models........................................................................................ 36 13 original fuel models .................................................................................. 36 40 fuel models ............................................................................................... 36 Custom fire behavior fuel models .......................................................................................... 38 BehavePlus .................................................................................................... 39 NEXUS ........................................................................................................... 42 Chapter 2 summary............................................................................................................... 45 Chapter 3: Characterizing a Forest Canopy for Fire Behavior Modeling ........... 46 Canopy fuel load (CFL)........................................................................................................... 50 Estimating canopy fuel load ........................................................................... 50 Canopy base height (CBH) ..................................................................................................... 51 Estimating canopy base height....................................................................... 52 Stand height (SH) .................................................................................................................. 54 Estimating stand height ................................................................................. 54 Canopy bulk density (CBD) .................................................................................................... 55 Estimating canopy bulk density ...................................................................... 56 Canopy Cover (CC) ................................................................................................................ 58 Estimating canopy cover ................................................................................ 58 Chapter 3 summary............................................................................................................... 59 Chapter 4: Characterizing Fuel Moisture Content ............................................. 60 Dead fuel moisture content .................................................................................................. 60 Relative importance of 1-, 10- and 100-hr timelag class moisture contents .... 61 Fuel moisture tables ...................................................................................... 64 Fuel conditioning ........................................................................................... 70 Live herbaceous fuel moisture content .................................................................................. 76 Live woody fuel moisture content ......................................................................................... 79 Foliar moisture content ......................................................................................................... 79 Chapter 4 summary............................................................................................................... 80 Chapter 5: Characterizing Slope Steepness and Aspect.................................... 82 2 Introduction to Wildfire Behavior Modeling Introduction Slope characteristics ............................................................................................................. 82 Slope steepness ............................................................................................. 82 Aspect ........................................................................................................... 84 Chapter 5 summary............................................................................................................... 85 Chapter 6: Characterizing Wind Speed and Direction ....................................... 86 Wind speed time-averaging period........................................................................................ 87 Reference height above ground ............................................................................................ 89 No-cover wind adjustment ............................................................................ 90 With-cover wind adjustment ......................................................................... 91 Overall wind adjustment................................................................................ 92 Specifying wind direction ...................................................................................................... 93 Chapter 6 summary............................................................................................................... 97 Chapter 7: Simulating Surface Fire Behavior ..................................................... 98 Rothermel spread model....................................................................................................... 98 Heat source ..................................................................................................100 Heat sink ......................................................................................................100 Spread equation ...........................................................................................101 Fireline intensity ..................................................................................................................102 Using non-spatial modeling systems .....................................................................................103 BehavePlus ...................................................................................................104 Using NEXUS.................................................................................................110 Chapter 7 summary..............................................................................................................112 Chapter 8: Simulating Crown Fire Spread Rate ............................................... 113 Rothermel correlation ..........................................................................................................113 Model of short-term potential .............................................................................................114 Spotting and crown fire growth ............................................................................................115 Using non-spatial modeling systems .....................................................................................115 BehavePlus ...................................................................................................116 NEXUS ..........................................................................................................118 Chapter 8 summary..............................................................................................................120 Chapter 9: Integrating Surface and Crown Fire Behavior Models ................... 121 Crown fire initiation 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