The Relative Importance of Fuels and Weather on Fire Behavior in Subalpine Forests

Abstract

Surface fire intensity (kilowatts per metre) and crown fire initiation were predicted using Rothermel's 1972 and Van Wagner's 1977 fire models with fuel data from 47 upland subalpine conifer stands varying in age from 22—258 yr and 35 yr of daily weather data (fuel moisture and wind speeds). Rothermel's intensity model was divided into a fuel component variable and weather component variable, which were then used to examine the relative roles of fuel and weather on surface fire intensity (kilowatts per metre). Similar variables were defined in the crown fire initiation model of Van Wagner. Both surface fire intensity and crown fire initiation were strongly related to the weather components and weakly related to the fuel components, due to much greater variability in weather than fuel, and stronger relationship to the fire behavior mechanisms for weather than for fuel. Fire intensity was correlated to annual area burned; large area burned years had higher fire intensity predictions than smaller area burned years. The reason for this difference was attributed directly to the weather variable frequency distribution, which was shifted towards more extreme values in years in which large areas burned. During extreme weather conditions, the relative importance of fuels diminishes since all stands achieve the threshold required to permit crown fire development. This is important since most of the area burned in subalpine forests has historically occurred during very extreme weather (i.e., drought coupled to high winds). The fire behavior relationships predicted in the models support the concept that forest fire behavior is determined primarily by weather variation among years rather than fuel variation associated with stand age.

Burned Area Mapping in the North American Boreal Forest Using Terra-MODIS LTDR (2001–2011): A Comparison with the MCD45A1, MCD64A1 and BA GEOLAND-2 Products

“…The primary driver of fire activity in the boreal forests of North America is the climate [39], but other factors, such as topography, vegetation and land use, also have a vital influence on spatial burn patterns [40]. In interior boreal regions, where large fires are most frequent, the influence of vegetation on fire size appears to be linked with flammability [41].…”

A second-order impact model for forest fire regimes

“…A first difficulty is that the model describes the behavior of a natural forest, while the great majority of available data refer to forests where fire-fighting efforts were systematically performed. A second and more important obstacle is that data do not refer to burned biomasses but rather to burned areas which are largely influenced by meteorological conditions (Bessie and Johnson (1995)). Under these circumstances, we can at most hope that some relevant features of forest fires (detectable from statistical analyses of field data) have some sort of analogy in the model behavior.…”

“…While it is true that natural forest fires originate from random events (mostly lightning) and are influenced by meteorological conditions (Bessie and Johnson (1995)), it is also true that fires can develop only if there is enough dry matter on the ground and if plants are sufficiently abundant in at least one of the various vegetational layers of the forest (for a relatively detailed discussion of this issue see Casagrandi and Rinaldi (1999) and references therein). This suggests the idea that long-term predictions of forest fires can be roughly performed with deterministic models describing the growth processes, while more precise short-term predictions can only be performed through stochastic models (conceptually comparable with those used in weather forecast).…”

“…The analysis of one or more stochastic versions of the model would be interesting, for example by letting the set X − of pre-fire conditions depend upon meteorological conditions. This would certainly amplify the chaoticity of the deterministic component of the system, thus giving to weather variability the role it deserves (Bessie and Johnson (1995)). The model could also be used to determine, at least qualitatively, the most important effects that climate change and different management policies (e.g.…”

Synoptic climatology of extreme fire-weather conditions across the southwest United States

“…The importance of weather conditions to the behavior and rate of spread of a wildfire is well documented (Flannigan and Harrington, 1988;Bessie and Johnson, 1995;Burgan et al, 1997;Flannigan and Wotton, 2001). Studies of the interaction between fire-weather conditions and wildfire activity have focused on modeling short timescale meteorologic and wildfire behavior variability (Fujioka, 1997;Andrews and Queen, 2001).…”