Coupled slope and wind effects on fire spread with influences of fire size: a numerical study using FIRETEC
F. Pimont A C , J.-L. Dupuy A and R. R. Linn BA Institut National de la Recherche Agronomique (INRA), UR 629 Ecology des Forêts Méditerranéennes Site Agroparc, F-84914 Avignon Cedex 9, France.
B Los Alamos National Laboratory (LANL), Earth and Environmental Sciences Division, Los Alamos, NM 87544, USA.
C Corresponding author. Email: pimont@avignon.inra.fr
Submitted: 22 August 2011 Accepted: 24 April 2012 Published: 13 July 2012
Abstract
Wind and slope are commonly accepted to be major environmental factors affecting the manner in which wildfires propagate. Fire-line width has been observed as having a significant effect on fire behaviour in some experimental fires. Most wildfire behaviour models and fire behaviour prediction systems take wind and slope effects into account when determining the rate of spread, but do not take into account the influence of fire width on the coupled effects of slope and wind. In the present study, the effect of topographic slope on rate of spread under weak (1 m s–1), moderate (5 m s–1) and strong (12 m s–1) wind speeds is investigated for two different initial fire widths (20 and 50 m) in a typical Mediterranean garrigue, using the coupled atmosphere–fire HIGRAD-FIRETEC model. The results show non-trivial combined effects and suggest a strong effect of fire width under low-wind conditions, especially for steep slopes. Simulated spread rates were compared with predictions of existing models of operational systems and a reasonable agreement was found. Additional exploratory simulations of fire behaviour in small canyons are provided. These simulations show how combined effects of wind, slope and fire-front size can induce different fire behaviours that operational models could fail to predict and provide insight that could be valuable for analysis of blow-up fires. These preliminary results also suggest that 3D physically based models could be used in the future to investigate how operational models can include non-local effects of fire propagation.
Additional keywords: blow-up, fire behaviour, fire length, fire width, physical modeling.
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