Search Fire Behavior Field Reference Guide, PMS 437

Text (indexed):
  1. Full Set PDF
  2. Elevation 0-500 feet (0-300 feet in Alaska), 30 in.
  3. Elevation 501-1,900 feet (301-1,700 feet in Alaska), 29 in.
  4. Elevation 1,901-3,900 feet (1,701-3,600 feet in Alaska), 27 in.
  5. Elevation 3,901-6,100 feet (3,601-5,700 feet in Alaska), 25 in.
  6. Elevation 6,101-8,500 feet (5,701-7,900 feet in Alaska), 23 in.
  7. Elevation 8,501-11,000 feet (above 7,900 feet in Alaska), 21 in.

The following tables calculate Dew Point and Relative Humidity based on the observed wet bulb and dry bulb temperatures and the elevation at the site of the observation. These can be calculated automatically using Wildland Fire RH Calculator Apps for iOS and Android available for free.

Full Set PDF

Click here to obtain a full set of tables in PDF form. Another available tool is an online Dew Point calculator.

Elevation 0-500 feet (0-300 feet in Alaska), 30 in.

Dry Bulb Temp 41-60

Psychometric Tables Pressure 30 in, DB Temp 41-60

Dry Bulb Temp 61-80

Psychometric Tables Pressure 30 In Mercury, DB Temp 61-80

Dry Bulb Temp 81-100

Psychometric Table, Pressure 30 in, DB Temp 81-100

Dry Bulb Temp 101-119

Psychometric Table, Pressure 30 in, DB Temp 81-100

Elevation 501-1,900 feet (301-1,700 feet in Alaska), 29 in.

Dry Bulb Temp 41-60

Psychometric Table, Pressure 29 in, DB Temp 41-60

Dry Bulb Temp 61-80

Psychometric Table, Pressure 29 in, DB Temp 61-80

Dry Bulb Temp 81-100

Psychometric Table, Pressure 29 in, DB Temp 81-100

Dry Bulb Temp 101-119

Psychometric Table, Pressure 29 in, DB Temp 101-119

Elevation 1,901-3,900 feet (1,701-3,600 feet in Alaska), 27 in.

Dry Bulb Temp 41-60

Psychometric Table, Pressure 27 in, DB Temp 41-60

Dry Bulb Temp 61-80

Psychometric Table, Pressure 27 in, DB Temp 61-80

Dry Bulb Temp 81-100

Psychometric Table, Pressure 27 in, DB Temp 81-100

Dry Bulb Temp 101-119

Psychometric Table, Pressure 27 in, DB Temp 101-119

Elevation 3,901-6,100 feet (3,601-5,700 feet in Alaska), 25 in.

Dry Bulb Temp 41-60

Psychometric Table, Pressure 25 in, DB Temp 41-60

Dry Bulb Temp 61-80

Psychometric Table, Pressure 25 in, DB Temp 61-80

Dry Bulb Temp 81-100

Psychometric Table, Pressure 25 in, DB Temp 81-100

Dry Bulb Temp 101-119

Psychometric Tables Pressure 25 in, DB Temp 101-119

Elevation 6,101-8,500 feet (5,701-7,900 feet in Alaska), 23 in.

Dry Bulb Temp 31-50

Psychometric Table, Pressure 23 in, DB Temp 31-50

Dry Bulb Temp 51-70

Psychometric Table, Pressure 23 in, DB Temp 51-70

Dry Bulb Temp 71-90

Psychometric Table, Pressure 23 in, DB Temp 71-90

Dry Bulb Temp 91-110

Psychometric Table, Pressure 23 in, DB Temp 91-109

Elevation 8,501-11,000 feet (above 7,900 feet in Alaska), 21 in.

Dry Bulb Temp 31-50

Psychometric Table, Pressure 21 in, DB Temp 31-50

Dry Bulb Temp 51-70

Psychometric Table, Pressure 21 in, DB Temp 51-70

Dry Bulb Temp 71-90

Psychometric Table, Pressure 21 in, DB Temp 71-90

 

 

Text (indexed):
  1. Canopy Cover-Percentage or Class
  2. Stand (Canopy)-Height-ft or m
  3. Canopy Base Height-ft or m
  4. Canopy Bulk Density-kg/m3 or lb/ft3

Canopy Cover - Percentage or Class

The forest Canopy Cover (CC) describes the percent cover or cover class of the tree canopy in a stand. Specifically, CC describes the vertical projection of the tree canopy onto an imaginary horizontal surface representing the ground’s surface. Estimate of CC is used in adjustment of 20 feet winds to mid-flame, fuel moisture conditioning and spotting distance models.

The scale illustrates representative CC percentages and ranges within each cover class.

Canopy Cover classification. This graphic depicts from above views of canopy cover and its effect on wind sheltering/reduction.

For surface fuels sheltered by a forest canopy on flat terrain. (Scott 2007)

Canopy CoverWind Sheltering
CC ≤ 5%Unsheltered
5% < CC ≤ 10%Partially Sheltered
10% < CC ≤ 15%Partially Sheltered
15% < CC ≤ 30%Fully Sheltered, Open
30% < CC ≤ 50%Fully Sheltered, Open
CC > 50%Fully Sheltered, Closed

Stand (Canopy) Height-ft or m

The Stand or Canopy Height (SH) describes the average height of the top of the vegetated canopy. SH estimates are used in adjustment of 20 feet winds to mid-flame and in spotting distance models.

Canopy Base Height-ft or m

The forest Canopy Base Height (CBH) describes the average height from the ground to a forest stand's canopy bottom. Specifically, it is the lowest height in a stand at which there is a sufficient amount of forest canopy fuel to propagate fire vertically into the canopy. Using this definition, ladder fuels such as lichen, dead branches, and small trees are incorporated. Estimate of CBH is used in the Crown Fire Initiation model.

Describing a Forest Canopy. This graphic highlights the way to think about the primary descriptors for crown fire prediction. Crown Bulk Density describes the crown fuel load and distribution. Stand Height describes height of canopy tops. Crown Base height represents the difficulty for surfaces fires to ignite the canopy. And Foliar Moisture content suggest how readily the canopy will burn.

Canopy Bulk Density-kg/m3 or lb/ft3

The forest Canopy Bulk Density (CBD) describes the density of available canopy fuel in a stand. It is defined as the mass of available canopy fuel per canopy volume unit. Typical units are either kg/m3 (LANDFIRE default) or lb/ft3 (BehavePlus default). CBD estimates are used to determine the threshold spread rate, or surface wind speed, used to determine the likelihood of active crown fire.

Canopy Bulk Density is a difficult concept to apply to crown fire predictions. This image shows that CBD varies with height above ground.

The following graph, also displayed in the Crown Fire section under Crown Fire Initiation and Propagation, displays the threshold surface 20 feet wind speed or Crowning Index, necessary for producing active crown fire given a specific canopy bulk density.

Crowning Index. Based on Rothermel crown fire spread model, canopy bulk density can be related to the windspeed required to sustain crown fire.

 

 

Text (indexed):
  1. Fuel Model Selection Guide
  2. Surface Fuel Model Evaluation
  3. Two Sets of Surface Fuel Models
  4. Moisture of Extinction
  5. Fuel Model Parameters and Descriptions
  6. Dynamic (proportional) Fuel Load Transfer

Fuel Model Selection Guide

* denotes dynamic fuel model with herbaceous fuel load transfer

Use this Fuel Model selection chart to help when considering alternative fuel model choices. It is based on moisture of extinction, presence of significant live fuel influence, and carrier fuel type.

In using this guide, these factors can guide users:

  1. Do diurnal changes in fuel moisture conditions bound the burn period each day, excluding much of the evening, overnight, and morning hours? If the answer is yes, consider primarily Low Moisture of Extinction fuel models over High Moisture of Extinction models.
  2. If specific fuelbeds seems unaffected by greenup and summer conditions, consider primarily dead fuels only fuel models during those periods.
  3. Consider what is carrying surface fire (Grass & Grass/Shrub, Shrub & Timber Understory, Timber Litter, or Slash/Blowdown) and select several alternatives.
  4. Dynamic Fuel Models (marked with *) allow greater variability due to seasonal transitions in live fuels. They are concentrated among the grass and grass shrub models primarily, due to the annual greenup and curing they experience. Note that SH1, SH9, TU1, and TU3 also include herbaceous fuel loads and are dynamic.
  5. Low, Moderate, and High classifications within each group reflect relative Heat per Unit Area levels. Use this classification to help focus selections on several alternatives.

Surface Fuel Model Evaluation

Once several alternative fuel models have been selected as possibilities, evaluation of their fire behavior outputs (rate of spread and flame length) with typical or reference inputs is important. However, making several good fuel model selections is only a preliminary step in the calibration process.

Fire Behavior ClassRate of Spread (ch/hr)Flame Length(ft)
Very Low0-20-1
Low2-51-4
Moderate5-204-8
High20-508-12
Very High50-15012-25
Extreme150+25+

As suggested here, when comparing modeled and observed fire behavior, it may be helpful to think of spread rates and flame lengths in ranges or Fire Behavior Classes. If fireline personnel can effectively report observed fire behavior in these terms, differentiating what they see through the burn period and as environmental inputs change, the analysis will be improved dramatically.

Testing the range of a fuel model’s characteristic fire behavior requires analysis of several environmental inputs. Consider these. BehavePlus, as a sensitivity tool, only allow consideration of two variables at a time. However, there are generally at least 3 significant environmental factors that govern the day-to-day variation in fire behavior; wind, slope, and fuel moisture. Fortunately, the Rothermel fire spread model depicts the effect of slope as an equivalent wind speed. If the calibration analysis represents the wind speed as a range of effective wind speed, slope should be at least generally incorporated. In some cases, it may still be necessary to consider its effect separately.

  • 1hr Moisture & Effective Wind Speed: The dominant factors wind, slope, and fuel mois Once a range of expected midflame wind speeds is established, it is possible to add the effect of slope by identifying the slope equivalent wind speed, producing a range of effective wind speeds for the calibration analysis.
  • Live Herbaceous Moisture: With other environmental inputs set at representative levels, evaluate the range of fire behavior produced between 30% and 120% live herbaceous fuel moisture for dynamic fuel models.
  • Live Woody Moisture: This consideration is critical for grass/shrub, shrub, and timber understory fuel models. Because there is no fuel load transfer in the live woody category, default ranges are characteristic of the current season. Set other environmental inputs at representative levels. Keep in mind that live woody moisture levels change rather slowly in most cases. Depending on the time of year and the drought situation, it may not be necessary to consider a wide range of moistures. However, it is critical that appropriate levels are identified for the analysis.
  • Slope and Spread Direction: Though this combination of factors is probably secondary in most cases, backing and flanking fire behavior related to slope reversals and prescribed fire ignitions may be important.

Two Sets of Surface Fuel Models

This guide integrates the original 13 models with the 40 standard models added in June of 2005. Though the developers of the 40 standard models intended that they stand alone, all 53 models are available to the user in current versions of all the fire modeling systems that are designed to use them. And though the original 13 models were grouped into only 4 carrier types, they can be effectively distributed into the 6 types defined with the newer set.

Consider the objectives that guided the development of these two sets.

The original 13 (Anderson, 1982) were designed to support analysis of:

  • Wildfires under peak fire conditions with cured herbaceous fuels.
  • Sensitivity to live fuels is represented in only 5 of them, with large responses predominately in fuel models 4 and 5.
  • They were designed before crown fire modeling was implemented, requiring that at least some of the 13 (fuel models 4, 6, and 7) represent crown fire behavior.See Active Crown Fire Behavior page for more information.

On the other hand, the newer 40 standard fuel models (Scott and Burgan, 2005) were developed to:

  • Facilitate analysis for fire use and fuel modification treatments.
  • They are designed so that they can represent green, growing season conditions as well as cured, peak season conditions.

The most important benefit of integrating fuel model sets in this guide may be the context the original 13 provide for users familiar with them. Consider it something of a dual language guide, facilitating translation for those users.

Moisture of Extinction

When selecting a fuel model, one of the first considerations should be whether fuels are expected to burn under high fuel moisture conditions. Though many modeling tools allow the user to define a burn period which can truncate fire behavior even when moisture of extinction has not been reached, humid climate fuel models (with high moisture of extinction) will express significant fire behavior even when corresponding dry climate fuels estimate no fire spread.

The example here demonstrates that GR4 exhibits no fire spread at 15% fuel moisture and at that same point, GR5 can project spread rates of as much as 50 ch/hr. Ensure that the fuel model selected accurately represents potential fire spread and intensity under the range of fuel moistures conditions that will be encountered.

This graph demonstrates the influence that Moisture of extinction exerts on the surface fire model. While GR4 and GR5 show similar spread rates under low fuel moisture, GR5 continues to show spread at much higher fuel moisture because it is defined by a much higher moisture of extinction.

Fuel Model Parameters and Descriptions

To ensure accuracy in modeling efforts, fuel model selection needs to employ a disciplined process. With the addition of 40 fuel models representing six carrier fuel types, users will be more likely to find an appropriate fuel model based on fuel model parameters, resulting in reasonable ranges of fire behavior over the range of anticipated environmental conditions.

  • Looking at the fuel bed, what fuel type (GR, GS, SH, TU, TL, or SB) is observed, or expected, to carry fire spread? Keep in mind that there are analogous characteristics that can cross these fuel types. However, if your fuelbed has a significant canopy layer, it may be more descriptive to select a TU or TL fuel.
  • Which fuel categories (1hr, 10hr, 100hr, Herb, Woody) are observed, or expected, to be available for burning in the flaming front under anticipated range of environmental conditions? Does one or several represent the distribution of fuel loads better than another?
  • Is it a shallow or deep fuelbed? Will any shrub layer burn as part of the surface or canopy layer?
  • Is the fuel model description a reasonable description of conditions encountered?

Dynamic and Proportional Fuel Load Transfer

A feature that was implemented with the development of the National Fire Danger Rating System (NFDRS) recognizes that most herbaceous fuels transition between green and cured conditions over the course of a fire season. The transfer of herbaceous fuel loads between live and dead categories redefines the fuel complex with each proportion transferred, making it a critical fuel model characteristic. The changes in output fire behavior can be dramatic when compared to the static fuel models among the original 13.

The example here shows spread rate for dynamic fuels GR6 and GR8 with the corresponding static FB3 from the original set of 13.

This graph demonstrates the influence that herbaceous fuel moisture exerts on the surface fire model. While GR6 and GR8 (“dynamic” models) are dramatically impacted, fuel model 3 (which is static) is not at all.

In the development of the new set of fuel models, this dynamic or proportional fuel load transfer has been implemented for all fuel models that include herbaceous loads. It includes all grass, grass/shrub, two shrub (SH1 & SH9), and two timber understory (TU1 & TU3) models.

As depicted in the graph and table below, the fuel load transfer (implemented in FARSITE, FLAMMAP, and WFDSS Fire Behavior analysis tools) is dependent on the input herbaceous moisture content.

Dynamic Fuel Load Transfer. For dynamic models, live herbaceous loads are transferred to dead fuel loads based on herbaceous fuel moisture. Transferred fuel loads are assigned the dead fine fuel moisture.

Herbaceous Moisture ContentLevel of Curing
(fuel load transferred)
Curing Classification
120% or more0/1 curedUncured
98%1/4 curedPartially cured
90%1/3 curedPartially cured
75%1/2 curedPartially cured
60%2/3 curedPartially cured
53%3/4 curedPartially cured
30% or less1/1 curedFully cured
  • If input Live Herbaceous Moisture Content (LHMC) is 120% or higher, none of the load is transferred.
  • If input LHMC is 30% or lower, the entire load is transferred to dead herbaceous fuel and the 1hr moisture content is assigned to it.
  • If input LHMC is between 30% and 120%, part of the herbaceous load is transferred to dead load and is assigned the 1hr moisture content. The input LHMC that represents a particular portion of the load transferred from live to dead can be calculated using this equation and an assumed curing percentage:

input LHMC = 120 - (90 X fraction cured)

Important cautions: Between 90% and 100% input LHMC, very rapid changes in fire behavior outputs can occur. Be sure to test the sensitivity to this input. Though it is agreed that live fuels can provide a critical influence on fire behavior, serving as both the heat sink and heat source in varying combinations, the specifics are not well modeled or understood. There are findings that indicate that curing is not directly related to herbaceous moisture content. As a result, BehavePlus allows the user to input curing % separate from LHMC.

 

 

Text (indexed):
  1. Carrier Fuel Types
  2. Grass and Grass Shrub Fuel Model Descriptions
  3. Shrub and Timber Understory Fuel Model Descriptions
  4. Timber Litter and Slash/Blowdown Fuel Model Descriptions

Carrier Fuel Types

Non-Burnable (NB) Fuels: The non-burnable fuel models are included on the next five pages to provide consistency in how the nonburnable portions of the landscape are displayed on a fuel model map. In all NB fuel models, there is no fuel load—wildland fire will not spread.

  • NB1 (091) –URBAN/SUBURBAN. Fuel model NB1 consists of land covered by urban and suburban development. To be called NB1, the area under consideration must not support wildland fire spread. In some cases, areas mapped as NB1 may experience structural fire losses during a wildland fire incident; however, structure ignition in those cases is either house-to-house or by firebrands, neither of which is directly modeled using fire behavior fuel models. If sufficient inflammable vegetation surrounds structures such that wildland fire spread is possible, then choose a fuel model appropriate for the wildland vegetation rather than NB1.
  • NB2 (092) – SNOW/ICE. Land covered by permanent snow or ice is included in NB2. Areas covered by seasonal snow can be mapped to two different fuel models: NB2 for use when snow-covered and another for use in the fire season.
  • NB3 (093) – AGRICULTURAL FIELD. Fuel model NB3 is agricultural land maintained in a non-burnable condition; examples include irrigated annual crops, mowed or tilled orchards, and so forth. However, there are many agricultural areas that are not kept in a non-burnable condition. For example, grass is often allowed to grow beneath vines or orchard trees, and wheat or similar crops are allowed to cure before harvest; in those cases, use a fuel model other than NB3.
  • NB8 (098) – OPEN WATER. Land covered by open bodies of water such as lakes, rivers and oceans.
  • NB9 (099) – BARE GROUND. Land devoid of enough fuel to support wildland fire spread is covered by fuel model NB9. Such areas may include gravel pits, arid deserts with little vegetation, sand dunes, rock outcroppings, beaches, and so forth.

Grass (GR) Fuels: The primary carrier of fire in the GR fuel models is grass. Grass fuels can vary from heavily grazed grass stubble or sparse natural grass to dense grass more than 6-feet tall. Fire behavior varies from moderate spread rate and low flame length in the sparse grass to extreme spread rate and flame length in the tall grass models. While the FB fuel models are static, all of the GR fuel models are dynamic, meaning that their live herbaceous fuel load shifts from live to dead as a function of live herbaceous moisture content. The effect of live herbaceous moisture content on spread rate and intensity is very strong.

Grass/Shrub (GS) Fuels: The primary carrier of fire in the GS fuel models is grass and shrubs combined; both components are important in determining fire behavior. All GS fuel models are dynamic, meaning that their live herbaceous fuel load shifts from live to dead as a function of live herbaceous moisture content. The effect of live herbaceous moisture content on spread rate and intensity is strong, and depends on the relative amount of grass and shrub load in the fuel model.

Shrub (SH) Fuels: The primary carrier of fire in the shrub fuel models is live and dead shrub twigs and foliage in combination with dead and down shrub litter. Fuel models SH1 and SH9 are dynamic, due to a small amount of herbaceous fuel loading in them. The effect of live herbaceous load transfer to dead fine fuel on spread rate and flame length can be significant in those two dynamic SH models.

Timber Understory (TU) Fuels: The primary carrier of fire in the TU fuel models is forest litter in combination with herbaceous or shrub fuels. TU1 and TU3 contain live herbaceous load and are dynamic, meaning that their live herbaceous fuel load is allocated between live and dead as a function of live herbaceous moisture content. The effect of live herbaceous moisture content on spread rate and intensity is strong, and depends on the relative amount of grass and shrub load in the fuel model.

Timber Litter (TL) Fuels: The primary carrier of fire in the TL fuel models is dead and down woody fuel. Live fuel, if present, has little effect on fire behavior.

Slash/Blow down (SB) Fuels: The primary carrier of fire in the SB fuel models is activity fuel or blow down. Forested areas with heavy mortality may be modeled with SB fuel models.

Grass and Grass Shrub Fuel Model Descriptions

GR and GS Dry Climate - Low Moisture of Extinction

(fuel models in green shaded rows: dynamic transfer of herb fuel load from live to dead)

CarrierFM #FM CodeFuel Model NameWind Adj1hr Load10hr Load100hr LoadHerb LoadWoody LoadTotal Load1hr SAVHerb SAVWoody SAVBed DepthMoist ExtinctDead HeatLive Heat
GR1FB1Short Grass0.360.7--------0.73500----1128000--
GR2FB2Timber grass and understory0.36210.50.5--430001500--11580008000
GR101GR1Short, sparse dry climate grass0.310.1----0.3--0.422002000--0.41580008000
GR102GR2Low load dry climate grass0.360.1----1--1.120001800--11580008000
GR104GR4Moderate load dry climate grass0.420.3----1.9--2.220001800--21580008000
GR107GR7High load dry climate grass0.461----5.4--6.420001800--31580008000
GS121GS1Low load dry climate grass-shrub0.350.2----0.50.71.42000180018000.91580008000
GS122GS2Moderate load dry climate grass-shrub0.390.50.5--0.612.62000180018001.51580008000

FB1 (01): Fire spread is governed by the fine herbaceous fuels that are cured or nearly cured. Fires move rapidly through cured grass and associated material. Very little shrub or timber is present, generally less than one-third of the area. Grasslands and savanna are represented along with stubble, grass tundra, and grass-shrub combinations that meet the above area constraint. Annual and perennial grasses are included fuels.

FB2 (02): Fire spread is primarily through fine herbaceous fuels, either curing or dead. These are surface fires where the herbaceous material, besides litter and dead-down stem wood from the open shrub or timber overstory, contribute to the fire intensity. Open shrub lands and pine stands or scrub oak stands that cover one-third or two thirds of the area may generally fit this model, but may include clumps of fuels that generate higher intensities and may produce firebrands. Some pinyon-juniper may be in this model.

GR1 (101): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is sparse grass, though small amounts of fine dead fuel may be present. The grass in GR1 is generally short, either naturally or by heavy grazing, and may be sparse or discontinuous. Moisture of extinction of GR1 is indicative of dry climate fuelbeds, but may also be applied in high-extinction moisture fuelbeds, because in both cases predicted spread rate and flame length are low compared to other GR models.

GR2 (102): Uses dynamic transfer of herb fuel load from live to dead. Primary carrier of fire is grass, though small amounts of fine dead fuel may be present. Load is greater than GR1. Fuelbed may be more continuous. Shrubs do not affect fire behavior.

GR4 (104): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is continuous, dry-climate grass. Load and depth are greater than GR2-fuelbed depth is about 2-feet.

GR7 (107): Uses dynamic transfer of herb fuel load from live to dead. Primary carrier is continuous dry-climate grass. Load and depth greater than GR4. Grass about 3-feet tall.

GS1 (121): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is grass and shrubs combined. Shrubs are about 1 foot high, grass load is low. Spread rate is moderate; flame length low. Moisture of extinction is low.

GS2 (122): Primary carrier is grass and shrubs combined. Shrubs are 1-3-feet high, grass load is moderate. Spread rate is high; flame length moderate. Moisture of extinction low.

GR and GS Humid Climate - High Moisture of Extinction

(fuel models in green shaded rows: dynamic transfer of herb fuel load from live to dead)

CarrierFM #FM CodeFuel Model NameWind Adj1hr Load10hr Load100hr LoadHerb LoadWoody LoadTotal Load1hr SAVHerb SAVWoody SAVBed DepthMoist ExtinctDead HeatLive Heat
GR3FB3Tall grass0.443--------31500----2.5258000--
GR103GR3Low load very coarse humid climate grass0.420.10.4--1.5--215001300--23080008000
GR105GR5Low load humid climate grass0.390.4----2.5--2.918001600--1.54080008000
GR106GR6Moderate load humid climate grass0.390.1----3.4--3.522002000--1.54090009000
GR108GR8High load very coarse humid climate grass0.490.51--7.3--8.815001300--43080008000
GR109GR9Very high load humid climate grass-shrub0.5211--9--1118001600--54080008000
GS123GS3Moderate load humid climate grass-shrub0.410.30.3--1.51.33.31800160016001.84080008000
GS124GS4High load humid climate grass-shrub0.421.90.30.13.47.112.81800160016002.14080008000

FB3 (03): Fires in this fuel are the most intense of the grass group and display high rates of spread under the influence of wind. The fire may be driven into the upper heights of the grass stand by the wind and cross standing water. Stands are tall, averaging about 3 ft., but may vary considerably. Approximately one-third or more of the stand is considered dead or cured and maintains the fire. Wild or cultivated grains that have not been harvested can be considered similar to tall prairie and marshland grasses.

GR3 (103): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is continuous, coarse, humid-climate grass. Grass and herb fuel load is relatively light; fuelbed depth is about 2 feet. Shrubs are not present in significant quantity to affect fire behavior.

GR5 (105): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is humid-climate grass. Load is greater than GR3 but depth is lower, about 1-2-feet.

GR6 (106): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is continuous humid-climate grass. Load is greater than GR5 but depth is about the same. Grass is less coarse than GR5.

GR8 (108): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is continuous, very coarse, humid-climate grass. Load and depth are greater than GR6. Spread rate and flame length can be extreme if grass is fully cured.

GR9 (109): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is dense, tall, humid-climate grass. Load and depth are greater than GR8, about 6-feet tall. Spread rate and flame length can be extreme if grass is fully or mostly cured.

GS3 (123): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire is grass and shrubs combined. Moderate grass/shrub load, average grass/shrub depth less than 2-feet. Spread rate is high; flame length moderate. Moisture of extinction is high.

GS4 (124): The primary carrier of fire is grass and shrubs combined. Heavy grass/shrub load, depth greater than 2-feet. Spread rate high; flame length very high. Moisture of extinction is high.

Shrub and Timber Understory Fuel Model Descriptions

SH and TU Dry Climate - Low Moisture of Extinction

Fuel models in green shaded rows: dynamic transfer of herb fuel load from live to dead

CarrierFM #FM CodeFuel Model NameWind Adj1hr Load10hr Load100hr LoadHerb LoadWoody LoadTotal Load1hr SAVHerb SAVWoody SAVBed DepthMoist ExtinctDead HeatLive Heat
SH4FB4Chapparal0.55542--5162000--150062080008000
SH5FB5Brush0.4210.5----23.52000--150022080008000
SH6FB6Dormant Brush0.441.52.52----61750----2.5258000--
SH141SH1Low load dry climate shrub0.360.30.300.21.3220001800160011580008000
SH142SH2Mod. load dry climate shrub0.361.42.40.8--3.98.42000--160011580008000
SH145SH5High load dry climate shrub0.553.62.1----2.98.6750--160061580008000
SH147SH7Very high load dry climate shrub0.553.55.32.2--3.414.4750--160061580008000
TU161TU1Light load dry climate timber-grass-shrub0.330.20.91.50.20.93.72000180016000.62080008000
TU164TU4Dwarf conifer with understory0.324.5------26.52300--20000.51280008000
TU165TU5Very high load dry climate timber-shrub0.33443--3141500--75012580008000
TU10FB10Timber litter and understory0.46325--2122000--150012580008000

FB4 (04): Fire intensity and fast-spreading fires involve the foliage and live and dead fine woody material in the shrub layer. Besides flammable foliage, there is dead woody material that significantly contributes to fire intensity. Deep litter layer may also confound suppression efforts.

FB5 (05): Primary carrier is litter cast by the shrubs, and the grasses or forbs in the understory. Shrubs are generally not tall, but have nearly total coverage of the area. Young, green stands with no deadwood.

FB6 (06): Fire carries through the shrub layer, requiring at least moderate winds. Fire will drop to the ground at low wind speeds or openings in the stand. The shrubs are older. A broad range of shrub conditions is included here.

SH1 (141):This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire in SH1 is woody shrubs and shrub litter. Low shrub fuel load, fuelbed depth about 1 foot; some grass may be present. Spread rate is very low; flame length very low.

SH2 (142): The primary carrier of fire in SH2 is woody shrubs and shrub litter. Moderate fuel load (higher than SH1), depth about 1 foot, and no grass fuel present. Spread rate is low; flame length low.

SH5 (145): The primary carrier of fire in GS4 is grass and shrubs combined. Heavy grass/shrub load, depth greater than 2-feet. Spread rate very high; flame length very high. Moisture of extinction is high.

SH7 (147): The primary carrier of fire is woody shrubs and shrub litter. Very heavy shrub load, depth 4-6-feet. Spread rate lower than SH5, but flame length similar. Spread rate is high; flame length very high.

FB10 (10): Dead down fuels include greater quantities of 3-inch or larger limbwood resulting from over maturity or natural events that create a large load of dead material. Crown fire and spotting is more frequent in this fuel situation.

TU1 (161): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire in is low load of grass and/or shrub with litter. Spread rate is low; flame length low.

TU4 (164): The primary carrier of fire is grass, lichen or moss understory plants. If live woody moisture content is set to 100 percent, this fuel model mimics the behavior of Norum’s (1982) empirical calibration for Alaska Black Spruce. Spread rate is moderate; flame length moderate.

TU5 (165): The primary carrier of fire in TU5 is heavy forest litter with a shrub or small tree understory. Spread rate is moderate; flame length moderate.

SH and TU Humid Climate - High Moisture of Extinction

Fuel models in green shaded rows: dynamic transfer of herb fuel load from live to dead

CarrierFM #FM CodeFuel Model NameWind Adj1hr Load10hr Load100hr LoadHerb LoadWoody LoadTotal Load1hr SAVHerb SAVWoody SAVBed DepthMoist ExtinctDead HeatLive Heat
SH7FB7Southern rough0.441.11.91.--0.44.91750--15002.54080008000
SH143SH3Mod. load humid climate shrub0.440.53----6.29.71600--14002.44080008000
SH144SH4Low load humid climate timber-shrub0.460.91.20.2--2.64.82000--160033080008000
SH146SH6Low load humid climate shrub0.422.91.5----1.45.8750--160023080008000
SH148SH8High load humid climate shrub0.462.13.40.9--4.410.7750--160034080008000
SH149SH9Very high load humid climate shrub0.54.52.5--1.6715.5750180015004.44080008000
TU162TU2Moderate load humid climate timber-shrub0.3611.81.3--0.24.22000--160013080008000
TU163TU3Moderate load humid climate timber-grass-shrub0.381.10.20.30.71.13.31800160014001.33080008000

FB7 (07): Fires burn through the surface and shrub strata with equal ease and can occur at higher dead fuel moisture contents because of the flammable nature of live foliage and other live material. Stands of shrubs are generally between 2-6 feet. high. Palmetto-gallberry understory within pine overstory sites are typical and low pocosins may be represented. Black spruce-shrub combinations in Alaska may also be represented.

SH3 (143): The primary carrier of fire in SH3 is woody shrubs and shrub litter. Moderate shrub load, possibly with pine overstory or herbaceous fuel, fuel bed depth 2-3-feet. Spread rate is low; flame length low.

SH4 (144): The primary carrier of fire in SH4 is woody shrubs and shrub litter. Low to moderate shrub and litter load, possibly with pine overstory, fuel bed depth about 3-feet. Spread rate is high; flame length moderate.

SH6 (146): The primary carrier of fire in SH6 is woody shrubs and shrub litter. Dense shrubs, little or no herbaceous fuel, fuelbed depth about 2-feet. Spread rate is high; flame length high.

SH8 (148): The primary carrier of fire in SH8 is woody shrubs and shrub litter. Dense shrubs, little or no herbaceous fuel, fuelbed depth about 3-feet. Spread rate is high; flame length high.

SH9 (149): This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire in SH9 is woody shrubs and shrub litter. Dense, finely branched shrubs with significant fine dead fuel, about 4-6-feet tall; some herbaceous fuel may be present. Spread rate is high, flame length very high.

TU2 (162): The primary carrier of fire in TU2 is moderate litter load with shrub component. High extinction moisture. Spread rate is moderate; flame length low.

TU3 (163):This model uses dynamic transfer of herb fuel load from live to dead. The primary carrier of fire in TU3 is moderate forest litter with grass and shrub components. Extinction moisture is high. Spread rate is high; flame length moderate.

Timber Litter and Slash/Blowdown Fuel Model Descriptions

Timber Litter

CarrierFM #FM CodeFuel Model NameWind Adj1hr Load10hr Load100hr LoadHerb LoadWoody LoadTotal Load1hr SAVHerb SAVWoody SAVBed DepthMoist ExtinctDead HeatLive Heat
TL8FB8Compact timber litter0.281.512.5----52000----0.2308000--
TL9FB9Hardwood litter0.282.90.40.2----3.52500----0.2258000--
TL181TL1Low load compact conifer litter0.2812.23.6----6.82000----0.2308000--
TL182TL2Low load broadleaf litter0.281.42.32.2----5.92000----0.2258000--
TL183TL3Moderate load conifer litter0.290.52.22.8----5.52000----0.3208000--
TL184TL4Small downed logs0.310.51.54.2----6.22000----0.4258000--
TL185TL5High load conifer litter0.331.22.54.4----8.12000----0.6258000--
TL186TL6Moderate load broadleaf litter0.292.41.21.2----4.82000----0.3258000--
TL187TL7Large downed logs0.310.31.48.1----9.82000----0.4258000--
TL188TL8Long-needle litter0.295.81.41.1----8.31800----0.3358000--
TL 189TL9Very high load broadleaf litter0.336.73.34.2----14.11800----0.6358000--

FB8 (08): Slow-burning ground fires with low flame heights are the rule, although the fire may encounter an occasional "jackpot" or heavy fuel concentration that can flare up. Only under severe weather conditions involving high temperatures, low humidities, and high winds do the fuels pose fire hazards. This layer is mainly needles, leaves, and some twigs since little undergrowth is present in the stand.

FB9 (09): Fire runs through the surface litter faster than FB8 and have higher flame height. Both long-needle conifer and hardwood stands, especially the oak-hickory types, are typical. Fall fires in hardwoods are representative, but spotting by rolling and blowing leaves in high winds will cause higher rates of spread than predicted. Concentrations of dead-down woody material will contribute to torching and spotting.

TL1 (181): The primary carrier of fire is compact forest litter. Light to moderate load, fuels 1-2 inches deep. May be used to represent a recently burned forest. Spread rate is very low; flame length very low.

TL2 (182): The primary carrier of fire is broadleaf (hardwood) litter. Low load, compact litter. Spread rate is very low; flame length very low.

TL3 (183): The primary carrier of fire is moderate load conifer litter, light load of coarse fuels. Spread rate is very low; flame length low.

TL4 (184): The primary carrier of fire is moderate load of fine litter and coarse fuels. Includes small diameter downed logs. Spread rate is low; flame length low.

TL5 (185): The primary carrier of fire is High load conifer litter; light slash or mortality fuel. Spread rate is low; flame length low.

TL6 (186): The primary carrier of fire is moderate load broadleaf litter, less compact than TL2. Spread rate is moderate; flame length low.

TL7 (187): The primary carrier of fire is heavy load forest litter, includes larger diameter downed logs. Spread rate low; flame length low.

TL8 (188): The primary carrier of fire in is moderate load long-needle pine litter, may include small amount of herbaceous load. Spread rate is moderate; flame length low.

TL9 (189): The primary carrier of fire is very high load, fluffy broadleaf litter. Can also be used to represent heavy needle-drape. Spread rate is moderate; flame length moderate.

Slash Blowdown

CarrierFM #FM CodeFuel Model NameWind Adj1hr Load10hr Load100hr LoadHerb LoadWoody LoadTotal Load1hr SAVHerb SAVWoody SAVBed DepthMoist ExtinctDead HeatLive Heat
SB11FB11Light slash0.361.54.55.5----11.51500----1158000--
SB12FB12Medium slash0.4341416.5----34.61500----2.3208000--
SB13FB13Heavy slash0.4672328.1----58.11500----3258000--
SB201SB1Low load activity fuel0.361.5311----15.52000----1258000--
SB202SB2Moderate load activity or low load blowdown0.364.54.34----12.82000----1258000--
SB203SB3High load activity fuel or moderate load blowdown0.385.52.83----11.32000----1.2258000--
SB204SB4High load blowdown0.455.33.55.3----142000----2.7258000--

FB11 (11): Fires are fairly active in the slash and intermixed herbaceous material. The spacing of the rather light fuel load, shading from overstory, or the aging of the fine fuels can contribute to limiting the fire potential. The less-than-3-inch material load is less than 12 tons per acre. The greater-than-3-inch material is represented by not more than 10 pieces, 4 inches in diameter, along a 50 feet transect.

FB12 (12): Rapidly spreading fires with high intensities capable of generating firebrands can occur. When fire starts, it is generally sustained until a fuel break or change in fuels is encountered. The visual impression is dominated by slash, most of it less than 3 inches in diameter. Fuels total less than 35 tons per acre and seem well distributed.

FB13 (13): Fire is generally carried across the area by a continuous layer of slash. Large quantities of greater-than-3-inch material are present. Active flaming is sustained for long periods and firebrands of various sizes may be generated. These contribute to spotting problems. Situations where the slash still has "red" needles attached but the total load is lighter, more like model 12, can be represented because of the earlier high intensity and quicker area involvement.

SB1 (201): Primary carrier of fire is light dead and down activity fuel. Fine fuel load is 10 to 20 t/ac, weighted toward fuels 1-3 in diameter class, depth is less than 1 foot. Spread rate is moderate; flame length low.

SB2 (202): The primary carrier of fire is moderate dead and down activity fuel or light blowdown. Fine fuel load is 7 to 12 t/ac, evenly distributed across 0-0.25, 0.25-1, and 1-3 inch diameter classes, depth is about 1 foot. Blowdown is scattered, with many trees still standing. Spread rate is moderate; flame length moderate.

SB3 (203): The primary carrier of fire is heavy dead and down activity fuel or moderate blowdown. Fine fuel load is 7 to 12 t/ac, weighted toward 0-0.25 inch diameter class, depth is more than 1 foot. Blowdown is moderate; trees compacted to near the ground. Spread rate is high; flame length high.

SB4 (204): The primary carrier of fire is heavy blowdown fuel. Blowdown is total, fuelbed not compacted, most foliage and fine fuel still attached to blowdown. Spread rate very high; flame length very high.

 

Text (indexed):
  1. Nelson Model 1 and 10-hr Fuel Moisture Estimation Methods
  2. Fosberg Model 1-hr Fuel Moisture Estimation Methods
  3. 10-hr, 100-hr and 1000-hr Fuel Moisture Content
  4. Fuel Moisture Conditioning in U.S. Spatial Fire Growth Models

Nelson Model 1 and 10-hr Fuel Moisture Estimation Methods

Ralph M. Nelson (2000) developed a fuel moisture model for estimating the diurnal fuel moisture changes in a 10-hr NFDRS fuelstick. Requiring hourly observations, it produces a more dynamic estimate that better reflects changes in precipitation, humidity and sunshine. 2016 NFDRS uses this methodology.

SimpleFFMC 1-hr Fuel Moisture Estimation Tables based on the Nelson Model, has been calibrated for the southeastern U.S. by W. Matt Jolly (2016) and is available as a web-app for online users.

Fosberg Model 1-hr Fuel Moisture Estimation Methods

Michael A. Fosberg and John E. Deeming (1971) documented procedures for estimating 1 and 10-hour Timelag Fuel Moistures. The methodology, along with seasonal adjustment tables, were integrated into Richard Rothermel’s (1983) tools and methods for surface fire behavior predictions. 78/88 NFDRS use this.

Daytime Estimation Procedure

  1. Using Table A, determine Reference Fuel Moisture (RFM). Percentage from intersection of temperature and relative humidity. Record this RFM percentage.
  2. Select Table B, C, or D to adjust RFM for local conditions by finding current month in table title.
  3. Is the fine fuel more than 50% shaded by canopies and clouds? If yes, use bottom shade) portion of table. If no, use top exposed portion of table.
  4. Determine the appropriate row based on aspect and slope.
  5. Determine the appropriate column based on time of day and elevation of area of concern when compared to the wx site elevation. Use (A)bove if the fire is 1-2000’ above your location, (B)elow if the fire is 1-2000’ below you, and (L)evel if the fire is within 1000’ above or below you.
  6. Obtain the 1-hr Moisture Content Correction (%) from the intersection of row and column.
  7. Add the resulting 1-hr Moisture Content Correction (%) to the Reference Fuel Moisture (%).

Nighttime Estimates of 1-hr Fuel Moisture

Published Reference Fuel Moisture and Correction Tables for Nighttime Conditions are not included here based on recommendation from Pat Andrews at the Missoula Fire Lab. She recommends:

  • Estimate Dry Bulb Temperature and RH for the location of interest.
  • Use Table A to estimate the Reference Fuel Moisture.
  • Use the appropriate 1-hr Moisture Content Correction Table based on the time of the year.
  • Obtain the correction for 0800, shaded conditions, and appropriate aspect from that table and add it to the Reference Fuel Moisture to estimate 1-hr moisture content for nighttime conditions.

Table A. Reference Fuel Moisture

1-hr Fuel Reference Fuel Moisture Table. Integrates Dry Bulb Temperature and Relative Humidity.

Table B. 1-hr Fuel Moisture Corrections-May-June-July

1-hr Fuel Moisture Corrections for May, June, and July. Used to adjust reference fuel moisture to local conditions of shading, slope, aspect, and time of day.

Table C. 1-hr Fuel Moisture Corrections-Feb-Mar-Apr and Aug-Sep-Oct

1-hr Fuel Moisture Corrections for February, March, April, August, September, and October. Used to adjust reference fuel moisture to local conditions of shading, slope, aspect, and time of day.

Table D. 1-hr Fuel Moisture Corrections-Nov-Dec-Jan

1-hr Fuel Moisture Corrections for November, December, and January. Used to adjust reference fuel moisture to local conditions of shading, slope, aspect, and time of day.

10-hr, 100-hr and 1000-hr Fuel Moisture Content

10-hr and 100-hr Fuel Moisture may be estimated in the following ways and applied along with the Fosberg fuel moistures in surface fire behavior predictions. 1000-hr fuel moisture is not usually needed for fire behavior calculations.

  • After estimating 1-hr moisture content, 10-hr and 100-hr fuel moisture content can be estimated by adding incremental amounts (e.g. adding 1-2% for 10-hr and 2-4% for 100-hr).
  • Using a local RAWS station or the Geographic Area’s Predictive Service summaries, 78/88 NFDRS moisture content estimates or forecast values that utilize the Fosberg Model may be available for each of these fuel categories.
  • The National Fuel Moisture Database may have sampling locations near your setting that have estimates for these fuel moistures.

In NFDRS, if danger rating calculations are suspended in the dormant season, default dormant fuel moistures are provided for 100-hr (10%-25%) and 1000-hr (15%-30%) fuel moistures when calculations are restarted in the spring. Default values are established with climate class designation for the location.

Fuel Moisture Conditioning in US Spatial Fire Growth Models

Deterministic spatial analyses in WFDSS (Basic, STFB, and NTFB) use estimates from historic weather data in the WIMS implementation of NFDRS as default initial fuel moistures inputs. Forecast and/or observed weather (for retrospective periods) from the selected weather stations are used to estimate hourly adjustments to dead fuel moistures for those analyses.  At this writing in 2019, initial dead fuel moistures in deterministic analyses default to estimates using the Fosberg dead fuel moisture model while conditioning weather uses the Nelson model to adjust 1-hr, 10-hr and 100-hr fuel moisture content over 1 to several days.. In most cases, one or two days of conditioning is sufficient. 

Take care to review the conditioning weather inputs for both observed and forecast days.  Precipitation amounts, high overnight humidity recovery, and/or significant cloud cover can raise fine fuel moisture significantly.  Use the Basic Outputs from Flammap or Short Term Fire Behavior analyses to review resulting 1-hr and 1-hr fuel moistures and edit inputs as necessary.

Desktop software (FLAMMAP and FARSITE) can use any initial fuel moisture and weather stream that the user supplies to apply these conditioning adjustments.

WFDSS FSPro draws its dead fuel moistures (1-hr, 10-hr, and 100-hr) in the ERC table from the WIMS implementation of NFDRS.  It ranks and groups ERC(g) values from the selected weather station climatology and provides average fuel moisture values from the underlying data for each of those groups, or percentile classes. As of this writing in 2019, it uses 78 Fuel Model G and the Fosberg model for all dead fuel moisture defaults. They are held static during the simulation and are not conditioned or changed during any simulation for the period that they are drawn from and used.

 

 

Text (indexed):

Concepts developed by Schroeder (1969) and adapted by Andrews, probability of ignition is estimated from:

  • Current temperature
  • Shading from either forest canopy or cloud cover
  • 1-hr fuel moisture content

Probability of Ignition. Combines influences of fine fuel moisture, dry bulb temperature, and shading.

 

 

 

Text (indexed):
  1. Concepts and Methods
  2. Growing Season Index (GSI)/Live Fuel Index (LFI)
  3. Herbaceous Fuel Moisture (HFM) Content
  4. Woody Fuel Moisture (WFM) Content
  5. Foliar Moisture Content (FMC)

Concepts and Methods

This table (Rothermel, 1983) suggests the fuel moisture associated with the phenology or stages of plant development through a year that includes dormancy.

Moisture Content (%)Stage of Vegetative Development
300%Fresh foliage, annuals developing early in the growing cycle
200%Maturing foliage, still developing, with full turgor
100%Mature foliage, new growth complete and comparable to older perennial foliage
50%Entering dormancy, coloration starting, some leaves may have dropped from stem
30%Completely cured, treat as dead fuel

Trends in live fuel moisture vary widely, but NFDRS and U.S. Fire Behavior Prediction methods categorize them as herbaceous and woody fuel moistures. NFDRS models trend live fuel moisture according to these stages of plant development:

  • During dormancy, all three models estimate herbaceous fuel moisture as if they were dead fine fuels. Minimum woody fuel moisture estimates vary, when dormant, according to the established Climate Class for the weather observing location.
  • Green-up/Green occurs in spring and early summer, when live fuel moistures trend from dormant minimums up to 250% under most favorable conditions.
  • Transition describes the process of progressive curing due to dry weather and soil conditions prior to frost and freezing conditions.
  • Freeze/Frozen conditions lead to rapid curing of live fuels into a dormant state at the end of the season if they haven’t already been fully cured in transition.

1978 NFDRS expects the user to identify a green-up date, after which live fuel moistures increase to maximum levels over a fixed number of days established by the climate class designation. After that, live fuel moistures transition trends follow 1000-hr (and x1000h) trends until fully cured or freeze/frozen conditions are selected.

1988 NFDRS replaced the green-up and transition trends with user selected designations of Season and greenness level for herbaceous and woody fuels.

2016 NFDRS uses a weather based index of plant development, called the Growing Season Index (GSI), to automate the process. It identifies when green-up begins, how fast it progresses, the maximum live fuel moisture, transition curing, and when freeze/frozen dormant conditions occur.

Growing Season Index (GSI) and Live Fuel Index (LFI)

The Growing Season Index (Jolly, et al, 2005) is a simple metric of plant physiological limits to photosynthesis. It is highly correlated to the seasonal changes in both the amount and activity of plant canopies. It predicts the green-up and senescence of live fuels and the influence of water stress events on vegetation. GSI is calculated as a function of the three indicators of important weather factors that regulate plant functions. These indicators are combined into a single indicator that integrates the limiting effects of temperature, water and light deficiencies. More information at https://www.wfas.net.

  • Minimum temperature: Many of the biochemical processes of plants are sensitive to low temperatures. Although ambient air temperatures certainly influence growth, constraints on phenology appear to be more closely related to restrictions on water uptake by roots when soil temperatures are suboptimal and many field studies show variable ecosystem responses over a range of minimum temperatures.
  • Vapor Pressure Deficit (VPD): Water stress causes partial to complete stomatal closure, reduces leaf development rate, induces the shedding of leaves, and slows or halts cell division. Although models are available to calculate a soil water balance, they require knowledge of rooting depth, soil texture, latent heat losses, and precipitation. As a surrogate, we selected an index of the evaporative demand, the vapor pressure deficit (VPD) of the atmosphere.
  • Photoperiod or Day Length: Photoperiod provides a plant with a reliable annual climatic cue because it does not vary from year to year at a given location. We assume that photoperiod provides the outer envelope within which other climatic controls may dictate foliar development. Studies have shown that photoperiod is important to both leaf flush and leaf senescence throughout the world.
  • The Live Fuel Index (LFI): May be referenced in some instances.  It represents the same value, only scaled between 0 and 100 instead of 0 and 1.

Example of 2014 seasonal values of the GSI and Live Fuel Moistures, Watford, North Dakota.

Growing Season Index and Live Fuel Moistures. This example graphic demonstrates the relationship between Growing Season Index (GSI) and the fuel moisture for live herbaceous and live woody fuels.

Upper and lower limits of the indicator functions used to calculate the Growing Season Index.

Input VariableUnconstrained (=1)Completely Limiting (=0)
Minimum Temperature5•C/41•F-2•C/28•F
Vapor Pressure Deficit (Pascals)900 Pascals4100 Pascals
Photoperiod (Day Length)11 hours10 hours

Example values of the GSI, their interpretation and effect on NFDRS Live Fuel Moistures.

GSI Increasing

GSI ValueClassification/Interpretation
0 to 0.5Pre green-up; dormancy. Herbaceous fuels at 30%, woody shrubs at dormant values at 50-80%.
>0.50Green-up; live fuel moisture increases linearly with GSI from dormant values.
0.5 to 1.0Closed green plant canopies. Live fuel moisture fluctuates with GSI. If GSI reaches 1.0 live moistures are limited to 250% for herbaceous fuels and 200% for live woody fuels.

GSI Decreasing

GSI ValueClassification/Interpretation
1.0 to 0.5Live fuel moisture fluctuates with GSI.
<0.50Leaf senescence.
Below 0.5Cured herbaceous and shrub dormancy. Herbaceous fuels at 30%, woody shrubs at dormant values.

The data and processing of the GSI, and the dependent live fuel moistures,make gridded map depictions possible and automated processing a reality.

Growing Season Index. Example graphic from the Wildland Fire Assessment System for March 4th of 2017.

Herbaceous Fuel Moisture (HFM) Content

As shown in this graph (Burgan, 1979), herbaceous fuel moisture influences both the flammability of living herbaceous vegetation and the transfer of living herbaceous fuel loads from and to dead 1-hr Time Lag (TL) fine fuels. The dashed line with the herbaceous load trend shows the trend for dynamic fire behavior fuel models.

Herbaceous Fuel Moisture Content Seasonal Trends. Stylized graphic that explains the phenological processes and the resulting manifestation of live fuel moisture content.

  • Herbaceous fuel moistures vary between 30% at dormancy and 250% at peak green-up.
  • Herbaceous loads are transferred to and from dead fine fuel loads based on fuel moisture. At 30%, all load is dead. At 120% all load is live.  Please see the content on Dynamic and Proportional Fuel Load Transfer on the Surface Fuel Model Selection page.
  • In 2016 NFDRS, herbaceous FM is at 30% when GSI is 0.5 or less and at 250% when GSI is at 1.0. HFM trends match GSI between 0.5 and 1.0.

Woody Fuel Moisture (WFM) Content

Though similar in trend to herbaceous fuel moisture content, woody fuel moisture content ranges with less extremes:

  • Dormant defaults range from 50% in climate class 1 - 80% in climate class 4.
  • Peak green conditions are represented by fuel moisture of 200%.
  • In 2016 NFDRS, min WFM is set at GSI of 0.5 or less, at 200% at GSI of 1.0 and trends with GSI between those levels.

There is no fuel load transfer between live and dead fuels based on woody fuel moisture.

This graphic shows the agreement between the Growing Season Index (GSI) trend and measured woody fuel moisture for Nevada sagebrush and California chamise, two very important fire landscapes. Note: difference from the 1978 NFDRS woody fuel moisture trend was based on the 1000hr fuel moisture trend.

Woody Fuel Moisture Calculation Method Comparison. This example graphic compares the Growing Season Index and its associated estimate of woody fuel moisture with the traditional approach to estimation in the 1978 version of NFDRS.

Foliar Moisture Content (FMC)

Foliar Moisture Content is defined (in the BehavePlus Variable) help as the moisture content of the conifer needles in tree crowns. It is used along with surface fire intensity and crown base height as input to the crown fire initiation model. Further, it is generally measured using only mature conifer needles at least one-year old.

In some cases, evergreen hardwoods and deciduous species with resinous leaves will carry crown fire. Estimates of foliar moisture should reflect flammability of these crown fuels.

BehavePlus allows a range of 30-300% as with other live fuels, but WFDSS allows only a range of 70-130%. Default value is typically 100%.

The example plot below, for Abies Lasiocarpa or Subalpine Fir, compares moisture content for new and old foliage (Agee, et al 2002).

Foliar Moisture Content. Example seasonal trend for Subalpine Fir.

As shown in this graph, there is a measurable Spring-Dip in measured foliar moisture content of mature needles associated with the emergence of new growth, at least among northern conifer (Hirsch, 1996 and Jolly,et.al., 2014).

Spring Dip in Foliar Moisture Content. Stylized graphic that demonstrates the influence of date and elevation on foliar moisture content as new needles flush and expand in the spring.

 

Text (indexed):

Wildland Fire Assessment System (WFAS) AVARR NDVI Greenness Reference is the comprehensive source of images, data archives, and methods for handling.

These images, derived from a satellite sensor, have been produced weekly since 1989, producing a historical record of vegetation phenology that can be used to characterize current vegetation greenness. They can be used to cross-reference with drought assessments and other characterizations of plant development, moisture stress, and curing. Cloud cover can have a significant impact on image quality in portions of the image.

While not an estimate of live fuel moisture, spatial distribution of NDVI estimates and its climatological derivatives can provide important insight to past and current vegetative state and overall landscape flammability during the growing season.

There are several depictions that allow you to evaluate the current NDVI status:

  • Normalized Difference Vegetation Index (ND) is the current derived value from which all the other climatological depictions are derived.
  • Departure from Average Greenness (DA) portrays the absolute difference between current value and the historic average greenness for the corresponding week of the year based on all years 1989-last year.
  • Relative Greenness (RG) portrays how green the vegetation is compared to how green it has been over the historical reference period (1989-last year). Because each pixel is normalized to its own historical range, all areas (dry to wet) can appear fully green at some time during the growing season.
  • Visual Greenness (VG) portrays vegetation greenness compared to a very green reference such as an alfalfa field or a golf course. The resulting image is like what you would expect to see from the air. Normally dry areas will never show as green as normally wetter areas.

This image of Departure from Average Greenness is for September 12, 2011

 Departure from Average Vegetative Greenness. Example graphic from the Wildland Fire Assessment System for September 12th of 2011.

 

 

Text (indexed):
  1. Online Fuel Moisture Sampling History
  2. Fuel Moisture Sampling Procedures

Online Fuel Moisture Sampling History

Fuel moisture sampling can provide useful insight to current conditions if it is done consistently throughout each fire season. Results from sampling efforts around the United States are stored in the National Fuel Moisture Database. Results for sampling history of both live and dead fuels are available for locations around the United States.

Fuel Moisture Sampling Procedures

General Guidelines

  • Record site name, date, time, observer name, observed weather, general site description.
  • DO NOT collect samples if water drops or dew are present on samples.
  • Keep samples in a cool and dry location.
  • Seal containers with tape that will not leave residue.

Live Fuel Samples

  • Only collect foliage or needles and very small twigs remove flowers, seeds, nuts, or berries.
  • Pack containers loosely to avoid spillage but ensure container is full.
  • Include stems of herbaceous plants.
  • Replace lid on container immediately after collecting sample.

Dead Fuel Samples

  • Samples should not be attached to live trees or shrubs.
  • Avoid decayed samples that crumble or splinter when rubbed.
  • Collect samples from several different plants.
  • Ensure container is full or about 20 grams.
  • Do not collect buried samples.
  • Pick samples of different size within the time lag class.
  • Recently fallen material should be avoided.
  • Remove all lichen, moss, and very loose bark from sample.

Duff and Soil Samples

  • Remove all soil and live tree or plant roots from sample.
  • Avoid any soil particles in duff samples and vice versa.

Litter Samples

  • Collect only uncompacted dry litter from both sunny and shady areas.

Handling and Measuring Samples

  • Preheat drying oven between 60°C (140°F) – 100°C (212°F). Be sure to note temp used.
  • Place sample cans with closed lids on scale and record wet weights.
  • Remove lid just prior to placing in oven. If material is lost, re-weigh sample
  • Dry sample for 24 hours (very wet samples 48 hours).
  • Replace Lids immediately after sample is removed from oven and weigh
  • Calculate fuel moisture using worksheet provided here:

Fuel moisture sampling and estimation. This table provides means for tracking sample weights and calculating gravimetric fuel moisture.

 

 

 

Text (indexed):

The NASA Short-term Prediction Research and Transition (SPoRT) Center has developed a Real-Time Land Information System (LIS), using satellite-derived datasets, ground-based observations, and model reanalysis to inform weather models with influences from the land surface.

Products are updated on a daily basis and include:

  • Volumetric Soil Moisture represents actual moisture in a soil column.
  • Relative Soil Moisture represents the soil moisture for a given soil column on a relative scale between soil saturation and wilting levels.
  • Column-Integrated Relative Soil Moisture combines 4 column depths down to 200cm.
  • Green Vegetation Fraction-current and trends-from VIIRS.
  • Land surface temperature and Heat Flux.

Soil Moisture products evaluate conditions at five levels:

  • 0-10 cm - relates most directly to the FWI Duff Moisture Code, or DMC
  • 10-40 cm - relates most directly to the FWI Drought Code, or DC
  • 40-100 cm
  • 100-200 cm
  • 0-200 cm Integrated Column

Available at 3km resolutions for the Continental U.S. (CONUS), analysts should consider using the following:

Column-Integrated Relative Soil Moisture products to assess current drought levels and changes over one week, two weeks, one month, three months, six months, and one year.

Green Vegetation Fraction products that are updated daily in lieu of NDVI that are updated on only a weekly basis. Current conditions are augmented by 1-month, 2-month, 3-month, 4-month, and 1-year change products.

Relative Soil Moisture products that may be correlated to fuel moisture contents applied in fire effects and fire spread models. A 0-10 cm 1-day change product provides an assessment of rainfall effects on the top soil layer that relates to fuel moisture in carrier fuels.

Relative Soil Moisture for top 2 centimeters. Example graphic from the SPoRT Land Information System for April 18th of 2017.