Abstract
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.
Highlights
The recognition of the significant influence of fuel moisture content (M) on fire rate of spread (R) is as old as fire research itself (e.g., Show, 1919)
Because natural mixed live and dead vegetation is difficult to reproduce indoors, laboratory studies have seldom been focused on fire spread in live fuel beds
Rossa (2017) used data from 185 burns under windless conditions in the absence of slope, covering a wide diversity of fuel bed composition, arrangement and M (6–179%) conditions, showing that the M-effect on R does not depend on vegetation condition
Summary
The recognition of the significant influence of fuel moisture content (M) on fire rate of spread (R) is as old as fire research itself (e.g., Show, 1919). Because natural mixed live and dead vegetation is difficult to reproduce indoors, laboratory studies have seldom been focused on fire spread in live fuel beds. The analysis of fire behaviour in fuel complexes including live components is usually derived from field studies. Counterintuitive, a review by Alexander & Cruz (2013) found no statistically significant relationship between field fires R and live fuel moisture content (Ml). Flammability tests on individual live fuel elements subjected to high radiative heat fluxes (up to 140 kW/m2) suggest a weak relationship between
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