Interdependencies between flame length and fireline intensity in predicting crown fire initiation and crown scorch height

2012 ◽  
Vol 21 (2) ◽  
pp. 95 ◽  
Author(s):  
Martin E. Alexander ◽  
Miguel G. Cruz
Keyword(s):  
Wildland Fire ◽  
Stem Bark ◽  
Flame Length ◽  
Flame Height ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Surface Fire ◽  
Crown Scorch ◽  
Fire Initiation ◽  
Bark Char

This state-of-knowledge review examines some of the underlying assumptions and limitations associated with the inter-relationships among four widely used descriptors of surface fire behaviour and post-fire impacts in wildland fire science and management, namely Byram’s fireline intensity, flame length, stem-bark char height and crown scorch height. More specifically, the following topical areas are critically examined based on a comprehensive review of the pertinent literature: (i) estimating fireline intensity from flame length; (ii) substituting flame length for fireline intensity in Van Wagner’s crown fire initiation model; (iii) the validity of linkages between the Rothermel surface fire behaviour and Van Wagner’s crown scorch height models; (iv) estimating flame height from post-fire observations of stem-bark char height; and (v) estimating fireline intensity from post-fire observations of crown scorch height. There has been an overwhelming tendency within the wildland fire community to regard Byram’s flame length–fireline intensity and Van Wagner’s crown scorch height–fireline intensity models as universal in nature. However, research has subsequently shown that such linkages among fire behaviour and post-fire impact characteristics are in fact strongly influenced by fuelbed structure, thereby necessitating consideration of fuel complex specific-type models of such relationships.

Corrigendum to: Interdependencies between flame length and fireline intensity in predicting crown fire initiation and crown scorch height

2017 ◽  
Vol 26 (4) ◽  
pp. 345 ◽  
Author(s):  
Martin E. Alexander ◽  
Miguel G. Cruz
Keyword(s):  
Wildland Fire ◽  
Stem Bark ◽  
Flame Length ◽  
Flame Height ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Surface Fire ◽  
Crown Scorch ◽  
Fire Initiation ◽  
Bark Char

This state-of-knowledge review examines some of the underlying assumptions and limitations associated with the inter-relationships among four widely used descriptors of surface fire behaviour and post-fire impacts in wildland fire science and management, namely Byram's fireline intensity, flame length, stem-bark char height and crown scorch height. More specifically, the following topical areas are critically examined based on a comprehensive review of the pertinent literature: (i) estimating fireline intensity from flame length; (ii) substituting flame length for fireline intensity in Van Wagner's crown fire initiation model; (iii) the validity of linkages between the Rothermel surface fire behaviour and Van Wagner's crown scorch height models; (iv) estimating flame height from post-fire observations of stem-bark char height; and (v) estimating fireline intensity from post-fire observations of crown scorch height. There has been an overwhelming tendency within the wildland fire community to regard Byram's flame length–fireline intensity and Van Wagner's crown scorch height–fireline intensity models as universal in nature. However, research has subsequently shown that such linkages among fire behaviour and post-fire impact characteristics are in fact strongly influenced by fuelbed structure, thereby necessitating consideration of fuel complex specific-type models of such relationships.

Simulated fire behaviour in young, postfire lodgepole pine forests

2017 ◽  
Vol 26 (10) ◽  
pp. 852 ◽  
Author(s):  
Kellen N. Nelson ◽  
Monica G. Turner ◽  
William H. Romme ◽  
Daniel B. Tinker
Keyword(s):  
Pinus Contorta ◽  
Stand Structure ◽  
Lodgepole Pine ◽  
Pine Forests ◽  
Fuel Moisture ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Fire Initiation ◽  
Moisture Conditions ◽  
Simulated Fire

Early-seral forests are expanding throughout western North America as fire frequency and annual area burned increase, yet fire behaviour in young postfire forests is poorly understood. We simulated fire behaviour in 24-year-old lodgepole pine (Pinus contorta var. latifolia) stands in Yellowstone National Park, Wyoming, United States using operational models parameterised with empirical fuel characteristics, 50–99% fuel moisture conditions, and 1–60kmhr−1 open winds to address two questions: [1] How does fireline intensity, and crown fire initiation and spread vary among young, lodgepole pine stands? [2] What are the contributions of fuels, moisture and wind on fire behaviour? Sensitivity analysis indicated the greatest contributors to output variance were stand structure mediated wind attenuation, shrub fuel loads and 1000-h fuel moisture for fireline intensity; crown base height for crown fire initiation; and crown bulk density and 1-h fuel moisture for crown fire spread. Simulation results predicted crown fire (e.g. passive, conditional or active types) in over 90% of stands at 50th percentile moisture conditions and wind speeds greater than 3kmhr−1. We conclude that dense canopy characteristics heighten crown fire potential in young, postfire lodgepole pine forests even under less than extreme wind and fuel moisture conditions.

Experimental modelling of crown fire initiation in open and closed shrubland systems

2014 ◽  
Vol 23 (4) ◽  
pp. 451 ◽  
Author(s):  
Watcharapong Tachajapong ◽  
Jesse Lozano ◽  
Shankar Mahalingam ◽  
David R. Weise
Keyword(s):  
Energy Transfer ◽  
Wind Speed ◽  
Wind Tunnel ◽  
Air Entrainment ◽  
Convective Heating ◽  
Crown Fire ◽  
Number Range ◽  
Surface Fire ◽  
Open Environment ◽  
Fire Initiation

The transition of surface fire to live shrub crown fuels was studied through a simplified laboratory experiment using an open-topped wind tunnel. Respective surface and crown fuels used were excelsior (shredded Populus tremuloides wood) and live chamise (Adenostoma fasciculatum, including branches and foliage). A high crown fuel bulk density of 6.8kgm–3 with a low crown fuel base height of 0.20m was selected to ensure successful crown fire initiation. Diagnostics included flame height and surface fire evolution. Experimental results were compared with similar experiments performed in an open environment, in which the side walls of the wind tunnel were removed. The effect of varying wind speed in the range 0–1.8ms–1, representing a Froude number range of 0–1.1, on crown fire initiation was investigated. The suppression of lateral entrainment due to wind tunnel walls influenced surface fire behaviour. When wind speed increased from 1.5 to 1.8ms–1, the rate of spread of surface fire and surface fire depth increased from 5.5 to 12.0cms–1 and 0.61 to 1.02m. As a result, the residence time of convective heating significantly increased from 16.0 to 24.0s and the hot gas temperature at the crown base increased from 994 to 1141K. The change in surface fire characteristics significantly affected the convective energy transfer process. Thus, the net energy transfer to the crown fuel increased so the propensity for crown fire initiation increased. In contrast, increasing wind speed decreased the tendency for crown fuel initiation in an open environment because of the cooling effect from fresh air entrainment via the lateral sides of surface fire.

scholarly journals Assessment of crown fire initiation and spread models in Mediterranean conifer forests by using data from field and laboratory experiments

2017 ◽  
Vol 26 (2) ◽  
pp. e02S ◽  
Author(s):  
Francisco Rodríguez y Silva ◽  
Mercedes Guijarro ◽  
Javier Madrigal ◽  
Enrique Jiménez ◽  
Juan R. Molina ◽  
...  
Keyword(s):  
Fire Spread ◽  
Full Scale ◽  
Research Centre ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Bench Scale ◽  
Fire Experiment ◽  
Fire Initiation ◽  
Scale Experiment

Aims of study: To conduct the first full-scale crown fire experiment carried out in a Mediterranean conifer stand in Spain; to use different data sources to assess crown fire initiation and spread models, and to evaluate the role of convection in crown fire initiation.Area of study: The Sierra Morena mountains (Coordinates ETRS89 30N: X: 284793-285038; Y: 4218650-4218766), southern Spain, and the outdoor facilities of the Lourizán Forest Research Centre, northwestern Spain.Material and methods: The full-scale crown fire experiment was conducted in a young Pinus pinea stand. Field data were compared with data predicted using the most used crown fire spread models. A small-scale experiment was developed with Pinus pinaster trees to evaluate the role of convection in crown fire initiation. Mass loss calorimeter tests were conducted with P. pinea needles to estimate residence time of the flame, which was used to validate the crown fire spread model.Main results: The commonly used crown fire models underestimated the crown fire spread rate observed in the full-scale experiment, but the proposed new integrated approach yielded better fits. Without wind-forced convection, tree crowns did not ignite until flames from an intense surface fire contacted tree foliage. Bench-scale tests based on radiation heat flux therefore offer a limited insight to full-scale phenomena.Research highlights: Existing crown fire behaviour models may underestimate the rate of spread of crown fires in many Mediterranean ecosystems. New bench-scale methods based on flame buoyancy and more crown field experiments allowing detailed measurements of fire behaviour are needed.

Modelling canopy fuel variables for Pinus radiata D. Don in NW Spain with low-density LiDAR data

2014 ◽  
Vol 23 (3) ◽  
pp. 350 ◽  
Author(s):  
Eduardo González-Ferreiro ◽  
Ulises Diéguez-Aranda ◽  
Felipe Crecente-Campo ◽  
Laura Barreiro-Fernández ◽  
David Miranda ◽  
...  
Keyword(s):  
Pinus Radiata ◽  
Airborne Lidar ◽  
Lidar Data ◽  
Low Density ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Fuel Characteristics ◽  
Fire Initiation ◽  
Behaviour Simulation ◽  
Simulation Systems

Crown fire initiation and spread are key elements in gauging fire behaviour potential in conifer forests. Crown fire initiation and spread models implemented in widely used fire behaviour simulation systems such as FARSITE and FlamMap require accurate spatially explicit estimation of canopy fuel complex characteristics. In the present study, we evaluated the potential use of very low-density airborne LiDAR (light detection and ranging) data (0.5 first returns m–2) – which is freely available for most of the Spanish territory – to estimate canopy fuel characteristics in Pinus radiata D. Don stands in north-western Spain. Regression analysis indicated strong relationships (R2=0.82–0.98) between LiDAR-derived metrics and field-based fuel estimates for stand height, canopy fuel load, and average and effective canopy base height Average and effective canopy bulk density (R2=0.59–0.70) were estimated indirectly from a set of previously modelled forest variables. The LiDAR-based models developed can be used to elaborate geo-referenced raster files to describe fuel characteristics. These files can be generated periodically, whenever new freely available airborne LiDAR data are released by the Spanish National Plan of Aerial Orthophotography, and can be used as inputs in fire behaviour simulation systems.

Re-analysis of wind and slope effects on flame characteristics of Mediterranean shrub fires

2015 ◽  
Vol 24 (7) ◽  
pp. 1001 ◽  
Author(s):  
Ralph M. Nelson
Keyword(s):  
Heat Transfer ◽  
Wildland Fire ◽  
Physical Modelling ◽  
Field Measurements ◽  
Heat Fluxes ◽  
Flame Height ◽  
Fire Behaviour ◽  
Dimensionless Variables ◽  
Mediterranean Shrub ◽  
Experimental Burns

During the past 20 years, study of wind–slope-aided wildland fire behaviour with experimental burns and physical modelling methods has increased. As part of their continuing study of fires in Mediterranean shrub, F. Morandini and X. Silvani reported experimental temperatures, heat fluxes, flame characteristics and other fire behaviour variables measured on five wind–slope-aided fires. Calculating convection numbers and several convective Froude numbers, the authors concluded that these dimensionless variables for their two wind-dominated fires did not satisfy criteria identified in previous studies for determining mechanisms of heat transfer during fuel preheating. The present paper describes a re-analysis of the data based on a triangular flame model and alternative definitions of flame tilt angle and height. This new analysis has shown that the influence of slope on the fire behaviour was not accounted for; thus, the conclusion of Morandini and Silvani is questionable. Of the five dimensionless variables studied using criteria in the literature, the squared flame height convective Froude number best describes modes of heat transfer to unburned fuels during the experimental fires. Though these results come indirectly from field measurements, they confirm the need to include slope effects in descriptions of wind–slope-aided fire behaviour.

A numerical study of flame geometry and potential for crown fire initiation for a wildfire propagating through shrub fuel

2007 ◽  
Vol 16 (5) ◽  
pp. 511 ◽  
Author(s):  
Dominique Morvan
Keyword(s):  
Numerical Study ◽  
Fire Hazard ◽  
Inertial Force ◽  
Numerical Results ◽  
Flame Height ◽  
Crown Fire ◽  
Radiation Emission ◽  
Understorey Vegetation ◽  
Surface Fire ◽  
Fuel Layer

The efficiency of fuel breaks installed in wildland–urban interfaces to reduce fire hazard depends strongly on the conditions of spread (rate of spread, flame height) of a surface fire through the shrub on the ground and also on the possibility of a transition for this fire from the understorey vegetation to the canopy. The aim of the present paper was to study (using numerical simulation with a physics-based model) the behaviour of surface fires propagating through Mediterranean shrub and to evaluate, from the characteristic dimensions of the flame, the onset of transition from a surface fire to a crown fire. The geometry of the flame was defined from the energy loss in the gas resulting from the radiation emission of soot particles, the flame contour was reconstructed from a threshold level fixed at 60 kW m–3. The numerical results were compared with experimental correlations of the geometry of the flame obtained for static and spreading fires. Extensive calculations were performed through a shrubland (Quercus coccifera and Brachypodium ramosum) for various fuel depths Hfuel ranging from 0.25 to 1.5 m and for wind speeds UH ranging from 1 to 10 m s–1. Then this study was extended to situations including a supplementary fuel layer representing the canopy of small trees (Pinus halepensis). The numerical results were analysed, introducing a dimensionless physical parameter, the Froude number, defined as the ratio between the inertial force due to the wind flow and the buoyancy. The results obtained with an upper fuel layer highlighted the role played by radiation heat transfer for the transition of surface fire to the crown. Some calculations were also carried out to study how a reduction of surface fuel on the ground can affect the vertical transition of the fire.

scholarly journals Examining fuel treatment longevity through experimental and simulated surface fire behaviour: a maritime pine case study

2009 ◽  
Vol 39 (12) ◽  
pp. 2529-2535 ◽  
Author(s):  
Paulo M. Fernandes
Keyword(s):  
Treatment Effectiveness ◽  
Residual Effect ◽  
Fire Spread ◽  
Flame Length ◽  
Maritime Pine ◽  
Fire Behaviour ◽  
Fuel Treatment ◽  
Surface Fire ◽  
Fire Modelling ◽  
The Difference

The adequate prediction of fire behaviour characteristics for both scientific and management objectives is deeply impacted by the performance of fire behaviour models. Both the lack of experimentation and limitations in fire modelling constrain current understanding of fuel treatment effectiveness and longevity. The residual effect of a 10-year-old prescribed fire was quantified by both simulating fire behaviour and observing real-world fire behaviour in treated (T10) and untreated (U25) fuels in a 25-year-old maritime pine ( Pinus pinaster Aiton) stand in Portugal. Fire behaviour characteristics were measured in experimental surface fires (n = 36). Surface-fire behaviour was simulated using BehavePlus with custom fuel models for T10, U25, and U15 (the untreated fuel complex when the stand was 15 years old). The T10 fuel complex had significantly less decomposing litter load and shrub cover and load than the U25 fuel complex. The observed rate of fire spread did not differ between fuel complexes after accounting for the effects of other environmental variables, but flame length in T10 was 25% lower than that in U25. BehavePlus simulations contradicted the difference observed in flame length. Inconsistent and misleading assessments of fuel treatment effectiveness with detrimental impacts on the outcomes of fuel management may result from the generalized practice of solely using simulation in lieu of experimental fires.

scholarly journals Assessing the probability of crown fire initiation based on fire danger indices

2003 ◽  
Vol 79 (5) ◽  
pp. 976-983 ◽  
Author(s):  
Miguel G Cruz ◽  
Martin E Alexander ◽  
Ronald H Wakimoto
Keyword(s):  
Logistic Regression ◽  
Forest Fire ◽  
Logistic Models ◽  
Fire Danger ◽  
Research Database ◽  
Crown Fire ◽  
Fire Behaviour ◽  
Wide Range ◽  
Fire Initiation ◽  
Fire Danger Indices

The initiation of crown fires in conifer stands was modelled through logistic regression analysis by considering as independent variables a basic physical descriptor of the fuel complex structure and selected components of the Canadian Forest Fire Weather Index (FWI) System. The study was based on a fire behaviour research database consisting of 63 experimental fires covering a relatively wide range of burning conditions and fuel type characteristics. Four models were built with decreasing input needs. Significant predictors of crown fire initiation were: canopy base height, wind speed measured at a height of 10 m in the open, and four components of the FWI System (i.e., Fine Fuel Moisture Code, Drought Code, Initial Spread Index and Buildup Index). The models predicted correctly the type of fire (i.e., surface or crown) between 90% and 66% of the time. The C index, a statistical measure, varied from 0.94 to 0.71, revealing good concordance between predicted probabilities and observed events. A comparison between the logistic models and Canadian Forest Fire Behaviour Prediction System models did not show any conclusive differences. The results of a limited evaluation involving two independent experimental fire data sets for distinctly different fuel complexes were encouraging. The logistic models built may have applicability in fire management decision support systems, allowing for the estimation of the probability of crown fire initiation at small and large spatial scales from commonly available fire environment and fire danger rating information. The relationships presented are considered valid for free-burning fires on level terrain in coniferous forests that have reached a pseudo steady-state and are not deemed applicable to dead conifer forests (i.e., insect-killed stands). Key words: Canadian Forest Fire Danger Rating System, crown fire initiation, fire behaviour, fire danger indices, logistic regression

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