Estimating the length-to-breadth ratio of elliptical forest fire patterns
Document Type: Conference Proceedings
Author(s): Martin E. Alexander
Publication Year: 1985

Cataloging Information

  • coniferous forests
  • crown fires
  • ellipse perimeter
  • field experimental fires
  • fire danger rating
  • fire growth
  • fire growth model
  • fuel types
  • ignition
  • nonlinear regression
  • overstory
  • rate of spread
  • wildfires
  • wind
  • wind driven fires
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Record Maintained By:
Record Last Modified: November 5, 2019
FRAMES Record Number: 10926
Tall Timbers Record Number: 1840
TTRS Location Status: In-file
TTRS Abstract Status: Fair use, Okay, Reproduced by permission

This bibliographic record was either created or modified by the Tall Timbers Research Station and Land Conservancy and is provided without charge to promote research and education in Fire Ecology. The E.V. Komarek Fire Ecology Database is the intellectual property of the Tall Timbers Research Station and Land Conservancy.


An empirical relationship was derived between the ratio of total length to maximum width or breadth (L/B) of wind-driven forest fires on level terrain originating from a point source ignition and the international standard 10-m open wind (W). The relation is based on the wind component of the relative spread index in the Canadian fire-danger rating system. The resulting equation, a nonlinear regression exhibiting a rising curve of increasing slope (L/B=1.0+0.00120 W^2.154), yields L/B equal to 1.0 at zero wind and approx. 6.5 at 50 km/h, the upper limit of application. Wind direction is assumed to remain fairly constant. Comparisons of predicted L/B values with actual observations extracted from experimental fires and well-documented wildfires in a variety of coniferous forests (n=18) by and large show good agreement (r=0.865). The L/B versus surface wind speed function is suitable for use in conjunction with a simple fire growth model for calculating the approximate size (area and perimeter length) of free-burning elliptical-shaped surface and crown fires spreading through fuel types with an overstory tree canopy, given the time elapsed and forward spread rate.

[This publication is referenced in the "Synthesis of knowledge of extreme fire behavior: volume I for fire managers" (Werth et al 2011).]

Online Link(s):
Alexander, M.E. 1985. Estimating the length-to-breadth ratio of elliptical forest fire patterns. Pages 287-304 in Proceedings of the 8th Conference on Fire and Forest Meteorology, April 29-May 2, 1985, Detroit, MI. Bethesda, MD: Society of American Foresters.