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The 10% wind speed rule of thumb for estimating a wildfire's forward rate of spread in forests and shrublands

Author(s): Miguel G. Cruz, Martin E. Alexander
Year Published: 2019
Description:

Key message: The collective analysis of a relatively large number of wildfire observations documented in conifer forests, dry eucalypt forests and temperate shrublands revealed that the forward rate of fire spread is roughly 10% of the average 10-m open wind speed, provided both are expressed in the same units (e.g. km h −1 ).

Context: Knowledge of a wildfire’s forward spread rate is a prerequisite for defining adequate fire suppression strategies and to ensure timely public warnings.

Aims: We wanted to investigate the possibility that a simple relationship exists that could be used as a first approximation for quickly estimating a wildfire’s spread rate simply from the open wind speed alone.

Methods: We analysed data from a number of high-intensity wildfire observations (n = 118) documented in temperate shrublands, Australian dry eucalypt forests and North American conifer forests to examine the suitability and soundness of a relationship between wind speed and rate of fire spread. We also contrasted the performance of the best function against established fire spread rate models for the three fuel types.

Results: The resulting rule of thumb is that the forward rate of spread of wildfires burning in forests and shrublands in relatively dry conditions is approximately equal to 10% of the average 10-m open wind speed, where both values are expressed in the same units.

Conclusion: The rule of thumb gives the most accurate results for dry fuel and high wind speed conditions with reduced bias and mean relative errors lower than 50%. Under these conditions, the error statistics are comparable to those obtained by the established fire spread rate models. The rule is not applicable to grasslands.

Citation: Cruz, Miguel G.; Alexander, Martin E. 2019. The 10% wind speed rule of thumb for estimating a wildfire's forward rate of spread in forests and shrublands. Annals of Forest Science 76:44. https://doi.org/10.1007/s13595-019-0829-8
Topic(s): Fire Behavior, Fuels
Ecosystem(s): None
Document Type: Book or Chapter or Journal Article
NRFSN number: 19774
FRAMES RCS number: 57791
Record updated: Jul 17, 2019