Assessing the probability of crown fire initiation based on fire danger indices

Abstract

The initiation of crown fires in conifer stands was modelled through logistic regression analysis by considering as independent variables a basic physical descriptor of the fuel complex structure and selected components of the Canadian Forest Fire Weather Index (FWI) System. The study was based on a fire behaviour research database consisting of 63 experimental fires covering a relatively wide range of burning conditions and fuel type characteristics. Four models were built with decreasing input needs. Significant predictors of crown fire initiation were: canopy base height, wind speed measured at a height of 10 m in the open, and four components of the FWI System (i.e., Fine Fuel Moisture Code, Drought Code, Initial Spread Index and Buildup Index). The models predicted correctly the type of fire (i.e., surface or crown) between 90% and 66% of the time. The C index, a statistical measure, varied from 0.94 to 0.71, revealing good concordance between predicted probabilities and observed events. A comparison between the logistic models and Canadian Forest Fire Behaviour Prediction System models did not show any conclusive differences. The results of a limited evaluation involving two independent experimental fire data sets for distinctly different fuel complexes were encouraging. The logistic models built may have applicability in fire management decision support systems, allowing for the estimation of the probability of crown fire initiation at small and large spatial scales from commonly available fire environment and fire danger rating information. The relationships presented are considered valid for free-burning fires on level terrain in coniferous forests that have reached a pseudo steadystate and are not deemed applicable to dead conifer forests (i.e., insect-killed stands).

Developing wildfire risk probability models for Eucalyptus globulus stands in Portugal

“…This is in concordance with other studies, where similar predicting variables have also been used as an indicator of stand-level competition and have been shown to influence fire risk probability (González et al 2006). Denser stands comprised of smaller trees are more prone to high-intensity crown fire due to high vertical and horizontal continuity (Van Wagner 1977, Cruz et al 2004. Wildfire occurrence probability also decreases with stand dominant height (hdom).…”

“…The rate of fuel accumulation after a wildfire in a eucalypt forest is relatively high, declining progressively after 5-8 years and stabilizing at a level that depends on the prevailing environmental conditions (Gould et al 2011). Moreover, the abundance of shrubs contributes to an easier spread of surface fires and facilitate the starting of crown fires because of the vertical fuel continuity (Rothermel & Philpot 1983, Finney 1999, Cruz et al 2004. From a fire suppression viewpoint, the effectiveness of silvicultural treatments can be gauged by their ability to prevent crown fires (Keeley & Zedler 2009).…”

Synthesis of knowledge of extreme fire behavior: volume I for fire managers

“…• Likelihood of crown fire initiation or occurrence based on two distinct approaches, one of which relies on the CBH or certain components of the Canadian FWI System (Cruz et al 2003b), whereas the other is determined by the fine dead fuel moisture (table 8-2), CBH, windspeed, and an estimate of surface fuel consumption ) ( fig. 8-17).…”

Science, technology, and human factors in fire danger rating: the Canadian experience.

“…Consequently, fire danger rating To avoid this tendency, the assumptions on which the systems are based and the range of conditions under which the systems are valid need to be defined carefully and checked frequently (Brown and Davis 1973). Most importantly, fire danger values must be correlated with empirical measures of fire occurrence or severity through experimentation and analysis of historical records (Harvey et al 1986;Viegas et al 1999;Cruz et al 2003). The use of fire danger systems can result in two types of error, which are illustrated for two conditions, 'High' and 'Low' fire danger levels in Table 2: • Type I errors (errors of commission or false positives) occur when the system 'sounds an alarm', but no real potential for serious fires exists: fire danger is overestimated; • Type II errors (errors of omission or false negatives) occur when serious fires take place prior to the system 'sounding an alarm' or when the system 'sounds no alarm at all': fire danger is underestimated.…”