Short communication: On the effect of live fuel moisture content on fire-spread rate

Aim of study: To reconcile the effects of live fuel moisture content (FMC) on fire rate of spread (ROS) derived from laboratory and field fires.Methods: The analysis builds on evidence from previous fire-spread experimental studies and on a comparison between two functions for the FMC damping effect: one derived from field burns, based on dead FMC, and another derived from laboratory trials, based on a weighted FMC (dead and live fuels).Main results: In a typical Mediterranean shrubland, laboratory and field-derived FMC damping functions are linearly related, which is explained by the correlation between monthly average live and dead FMC variation throughout the year. This clarifies why the effect of live FMC on real-world fires ROS has remained elusive.Research highlights: By providing evidence that the most significant effect of FMC on ROS is independent of vegetation phenology (dead or live condition), and explaining why in specific situations dead FMC is sufficient to provide satisfactory ROS predictions, our results can assist future modelling efforts.

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Live Fuel Moisture Content: The ‘Pea Under the Mattress’ of Fire Spread Rate Modeling?

Fire ◽

10.3390/fire1030043 ◽

2018 ◽

Vol 1 (3) ◽

pp. 43 ◽

Cited By ~ 9

Author(s):

Carlos Rossa ◽

Paulo Fernandes

Keyword(s):

Moisture Content ◽

Fire Spread ◽

High Heat ◽

Heat Fluxes ◽

Fuel Moisture ◽

Spread Rate ◽

Live Fuels ◽

Live Fuel Moisture ◽

Live Tree ◽

Fuel Moisture Content

Currently, there is a dispute on whether live fuel moisture content (FMC) should be accounted for when predicting a real-world fire-spread rate (RoS). The laboratory and field data results are conflicting: laboratory trials show a significant effect of live FMC on RoS, which has not been convincingly detected in the field. It has been suggested that the lack of influence of live FMC on RoS might arise from differences in the ignition of dead and live fuels: flammability trials using live leaves subjected to high heat fluxes (80–140 kW m−2) show that ignition occurs before all of the moisture is vaporized. We analyze evidence from recent studies, and hypothesize that differences in the ignition mechanisms between dead and live fuels do not preclude the use of overall fine FMC for attaining acceptable RoS predictions. We refer to a simple theory that consists of two connected hypotheses to explain why the effect of live FMC on field fires RoS has remained elusive so far: H1, live tree foliage FMC remains fairly constant over the year; and H2, the seasonal variation of live shrubs’ FMC correlates with the average dead FMC. As a result, the effect of live FMC is not easily detected by statistical analysis.

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A generic, empirical-based model for predicting rate of fire spread in shrublands

International Journal of Wildland Fire ◽

10.1071/wf14130 ◽

2015 ◽

Vol 24 (4) ◽

pp. 443 ◽

Cited By ~ 64

Author(s):

Wendy R. Anderson ◽

Miguel G. Cruz ◽

Paulo M. Fernandes ◽

Lachlan McCaw ◽

Jose Antonio Vega ◽

...

Keyword(s):

Moisture Content ◽

Experimental Studies ◽

Fire Spread ◽

Fuel Moisture ◽

Fire Behaviour ◽

Weather Factors ◽

Vegetation Height ◽

Rate Of Spread ◽

Wide Range ◽

Fuel Moisture Content

A shrubland fire behaviour dataset was assembled using data from experimental studies in Australia, New Zealand, Europe and South Africa. The dataset covers a wide range of heathlands and shrubland species associations and vegetation structures. Three models for rate of spread are developed using 2-m wind speed, a wind reduction factor, elevated dead fuel moisture content and either vegetation height (with or without live fuel moisture content) or bulk density. The models are tested against independent data from prescribed fires and wildfires and found to predict fire spread rate within acceptable limits (mean absolute errors varying between 3.5 and 9.1 m min–1). A simple model to predict dead fuel moisture content is evaluated, and an ignition line length correction is proposed. Although the model can be expected to provide robust predictions of rate of spread in a broad range of shrublands, the effects of slope steepness and variation in fuel quantity and composition are yet to be quantified. The model does not predict threshold conditions for continuous fire spread, and future work should focus on identifying fuel and weather factors that control transitions in fire behaviour.

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A laboratory-based quantification of the effect of live fuel moisture content on fire spread rate

International Journal of Wildland Fire ◽

10.1071/wf15114 ◽

2016 ◽

Vol 25 (5) ◽

pp. 569 ◽

Cited By ~ 21

Author(s):

Carlos G. Rossa ◽

Ricardo Veloso ◽

Paulo M. Fernandes

Keyword(s):

Moisture Content ◽

Laboratory Experiments ◽

Fire Spread ◽

Fuel Moisture ◽

Drying Process ◽

Spread Rate ◽

Rate Of Spread ◽

Live Fuels ◽

Fuel Moisture Content ◽

Content Range

Observational evidence of an effect of live vegetation moisture content on fire spread rate remains extremely scarce despite the significance of fire activity in fuel complexes dominated by live components. This study assessed the moisture content effect of quasi-live fuels on fire spread rates measured in laboratory experiments. Fuel beds were built by vertically placing vegetation clippings to reproduce the natural upright fuel structure. The fuel drying process during storage resulted in a wide moisture content range (13–180%). An exponential damping function was fitted to rate of spread observations in four fuel types, indicating that rate of spread is halved by an increase in live moisture content from 50 to 180%. This effect, especially at higher moisture contents, was weaker than that predicted by theoretical formulations and from studies in mixtures of dead and live fuel.

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Empirical modelling of surface fire behaviour in maritime pine stands

International Journal of Wildland Fire ◽

10.1071/wf08023 ◽

2009 ◽

Vol 18 (6) ◽

pp. 698 ◽

Cited By ~ 51

Author(s):

Paulo M. Fernandes ◽

Hermínio S. Botelho ◽

Francisco C. Rego ◽

Carlos Loureiro

Keyword(s):

Wind Speed ◽

Moisture Content ◽

Fire Spread ◽

Fire Intensity ◽

Fuel Moisture ◽

Fire Behaviour ◽

Spread Rate ◽

Surface Fire ◽

Rate Of Spread ◽

Fuel Moisture Content

An experimental burning program took place in maritime pine (Pinus pinaster Ait.) stands in Portugal to increase the understanding of surface fire behaviour under mild weather. The spread rate and flame geometry of the forward and backward sections of a line-ignited fire front were measured in 94 plots 10–15 m wide. Measured head fire rate of spread, flame length and Byram’s fire intensity varied respectively in the intervals of 0.3–13.9 m min–1, 0.1–4.2 m and 30–3527 kW m–1. Fire behaviour was modelled through an empirical approach. Rate of forward fire spread was described as a function of surface wind speed, terrain slope, moisture content of fine dead surface fuel, and fuel height, while back fire spread rate was correlated with fuel moisture content and cover of understorey vegetation. Flame dimensions were related to Byram’s fire intensity but relationships with rate of spread and fine dead surface fuel load and moisture are preferred, particularly for the head fire. The equations are expected to be more reliable when wind speed and slope are less than 8 km h–1 and 15°, and when fuel moisture content is higher than 12%. The results offer a quantitative basis for prescribed fire management.

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Soil Moisture and Live Fuel Moisture Content as key remote sensing variables to unlock improved wildfire predictions

10.5194/egusphere-egu21-15159 ◽

2021 ◽

Author(s):

Florian Briquemont ◽

Akli Benali

Keyword(s):

Soil Moisture ◽

Moisture Content ◽

Fire Risk ◽

Simulation Models ◽

Fire Spread ◽

Fuel Moisture ◽

Live Fuel Moisture ◽

Risk Maps ◽

Fuel Moisture Content ◽

The Impact

Large wildfires are amongst the most destructive natural disasters in southern Europe, posing a serious threat to both human lives and the environment.Although wildfire simulations and fire risk maps are already very a useful tool to assist fire managers in their decisions, the complexity of fire spread and ignition mechanisms can greatly hinder their accuracy. An important step in improving the reliability of wildfire prediction systems is to implement additional drivers of fire spread and fire risk in simulation models.Despite their recognized importance as factors influencing fuel flammability and fire spread, soil moisture and live fuel moisture content are rarely implemented in the simulation of large wildfires due to the lack of sufficient and accurate data. Fortunately, new satellite products are giving the opportunity to assess these parameters on large areas with high temporal and spatial resolution.The purpose of this study is twofold. First, we aimed to evaluate the capabilities of satellite data to estimate soil moisture and live fuel moisture content in different landcovers.&#160; Secondly, we focused on the potential of these estimates for assessing fire risk and fire spread patterns of large wildfires in Portugal. Ultimately, the goal of this study is to implement these estimated variables in fire spread simulations and fire risk maps. We compared datasets retrieved from Sentinel 1, SMAP (Soil Moisture Active Passive radiometer) and MODIS (Moderate Resolution Imaging Spectrometer) missions. Several estimators of LFMC based on spectral indices were tested and their patterns were compared with field data. Based on these estimators, we assessed the impact of LFMC and soil moisture on the extent and occurrence of large wildfires. Finally, we built a database of detailed historical wildfire progressions, which we used to evaluate the influence of soil moisture and LFMC on the velocity and direction of the fire spread.

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The initiation of fire spread in shrubland fuels recreated in the laboratory

International Journal of Wildland Fire ◽

10.1071/wf09038 ◽

2010 ◽

Vol 19 (4) ◽

pp. 512 ◽

Cited By ~ 22

Author(s):

Matt P. Plucinski ◽

Wendy R. Anderson ◽

Ross A. Bradstock ◽

A. Malcolm Gill

Keyword(s):

Moisture Content ◽

Classification Tree ◽

Fire Spread ◽

Fuel Moisture ◽

Shrub Layer ◽

Moisture Contents ◽

Layer Density ◽

Live Fuel Moisture ◽

Fuel Moisture Content ◽

The Impact

Fire-prone shrub-dominated vegetation communities cover a considerable portion of Australia, including areas fringing urban development. Near urban interfaces, they are actively managed with prescribed fire to reduce the risk of wildfire (unplanned fire). Knowledge of the range of conditions that allow fires to spread or fail to do so is limited and can inconvenience fire managers when conducting prescribed burns. A series of experimental ignitions conducted in miniature shrublands reconstructed in the laboratory were used to investigate factors that influence ignition thresholds. The miniature shrublands were composed of foliage from the shrub Allocasuarina nana and were prepared over a range of moisture contents and densities. The impact of dead fuel within the aerial structure of the shrubs was also investigated, as was the presence and absence of wind and litter. The most important factors for spread initiation were identified using logistic regression analysis and classification tree modelling. The presence of litter, live fuel moisture content, shrub-layer density, presence of wind, and the amount and continuity of the dead elevated fuel were all found to influence spread sustainability. There was a negative interaction between shrub-layer density and live fuel moisture content, showing the effect of density to be less at higher moisture contents.

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Effects of distribution of bulk density and moisture content on shrub fires

International Journal of Wildland Fire ◽

10.1071/wf12040 ◽

2013 ◽

Vol 22 (5) ◽

pp. 625 ◽

Cited By ~ 11

Author(s):

Ambarish Dahale ◽

Selina Ferguson ◽

Babak Shotorban ◽

Shankar Mahalingam

Keyword(s):

Moisture Content ◽

Spatial Variation ◽

Bulk Density ◽

Solid Fuel ◽

Numerical Solutions ◽

Propagation Speed ◽

Fire Spread ◽

Fuel Moisture ◽

Combustion Heat ◽

Fuel Moisture Content

Formulation of a physics-based model, capable of predicting fire spread through a single elevated crown-like shrub, is described in detail. Predictions from the model, obtained by numerical solutions to governing equations of fluid dynamics, combustion, heat transfer and thermal degradation of solid fuel, are found to be in fairly good agreement with experimental results. In this study we utilise the physics-based model to explore the importance of two parameters – the spatial variation of solid fuel bulk density and the solid fuel moisture content – on the burning of an isolated shrub in quiescent atmosphere. The results suggest that vertical fire spread rate within an isolated shrub and the time to initiate ignition within the crown are two global parameters significantly affected when the spatial variation of the bulk density or the variation of fuel moisture content is taken into account. The amount of fuel burnt is another parameter affected by varying fuel moisture content, especially in the cases of fire propagating through solid fuel with moisture content exceeding 40%. The specific mechanisms responsible for the reduction in propagation speed in the presence of higher bulk densities and moisture content are identified.

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