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Background: Wildfire propagation is inherently non-steady, although forecasts of their spread focus on a pseudo-steady state assumption. Aims: To investigate the variability in rate of fire spread of wildfires in southern Australian grassland landscapes, and the effect of landscape features in inhibiting fire propagation. To evaluate the adequacy of grassfire rate of spread models currently used in Australia. Methods: We reconstructed the propagation of six wildfires in grassland fuels and characterised the unsteady nature of rate of spread. We also analysed the effect of barriers to fire spread in slowing or halting wildfire propagation. Key results: Headfire rate of spread in wildfires was observed to be non-steady, with peaks in forward rate of spread being on average 2.6-times higher than mean values. The rate of spread had an average coefficient of variation of 88%. Areas of fuel discontinuity, such as roads, did not stop fires under moderate burning conditions, but resulted in slowing the average rate of fire spread. Conclusions: Analysis of wildfire observations is key to understand fire behaviour features that are not replicable in experimental or modelling environments. Findings from the analysis can support fire-fighting safety awareness and inform landscape fire propagation modelling. This study uses detailed wildfire observation data to describe non-steady headfire rate of spread and the effect of barriers to fire propagation, such as roads, on halting or inhibiting spread. We discuss the implications for wildfire spread modelling and fireline safety. [ABSTRACT FROM AUTHOR]

Background: Development of the Australian Fire Danger Rating System began in 2017 with a project aimed at demonstrating the feasibility of a new fire danger rating system through a Research Prototype (AFDRSRP) that accounted for variability in Australian vegetation types, was nationally applicable, modular and open to continuous improvement. Aims: In this manuscript, we identify and define transition points and categories for the AFDRSRP. We discuss user responses to the categorisation during a live trial evaluation of the AFDRSRP and reflect on limitations and potential improvements. Methods: A review of available literature, broad consultation with stakeholders and reanalysis of fire impact data were used to determine suitable thresholds for categorising fire danger within the AFDRSRP. Key results: Fire danger categories within the AFDRSRP reflect transitions in fire behaviour that result in application of different fire management strategies or are associated with variation in serious consequences and impacts. Conclusions: The AFDRSRP incorporated the best available science, supported by a well-defined framework for categorising and defining fire danger making it suitable for application across Australian fire jurisdictions and range of fuel types. Implications: The framework allows fire managers to assess the accuracy and appropriateness of forecasted fire danger. We identify and present defined categories and thresholds for the Australian Fire Danger Rating System: Research Prototype based on reflecting transitions in fire behaviour that result in application of different fire management strategies or associated with variation in potential for serious consequences and impacts. This article belongs to the Collection Australian Fire Danger Rating System. [ABSTRACT FROM AUTHOR]

Methods were developed to predict the moisture content of the elevated dead fine fuel layer in gorse (Ulex europaeus L.) shrub fuels. This layer has been observed to be important for fire development and spread in these fuels. The accuracy of the Fine Fuel Moisture Code (FFMC) of the Canadian Fire Weather Index System to predict the moisture content of this layer was evaluated. An existing model was used to determine the response time and equilibrium moisture content from field data. This response time was incorporated into a bookkeeping model, combining the FFMC and this response time--equilibrium moisture content model. The FFMC poorly predicted the elevated dead fuel moisture content in gorse fuels, and attempts to improve its accuracy through regression modelling were unsuccessful. The response time of the elevated dead fine fuel layer was very fast (38-77 min) and has important implications for fire danger rating. The bookkeeping approach was the most promising method to predict elevated dead fuel moisture content. A limitation was the inability to model fuel-level meteorology. However, this model warrants further validation and extension to other shrub fuels and could be incorporated into existing fire danger rating systems that can utilize hourly weather data. Resume: Des methodes ont ete developpees pour predire la teneur en humidite dans la strate aerienne de combustibles ligneux morts parmi les combustibles arbustifs constitues d'ajonc d'Europe (Ulex europaeus L.). Les observations revelent que cette strate de combustible joue un role important dans le developpement et la propagation du feu dans ces combustibles. La justesse de l'indice du combustible leger (ICL) de la methode canadienne de l'indice foret-meteo a ete evaluee pour predire la teneur en humidite de cette strate de combustibles. Un modele existant a ete utilise pour determiner le temps de reponse et le degre d'humidite d'equilibre (DHE) a partir de donnees de terrain. Le temps de reponse a ete incorpore dans un modele de comptabilite qui combinait l'ICL et ce modele de temps de reponse et de DHE. L'ICL predisait mal la teneur en humidite de la strate aerienne de combustibles morts parmi les combustibles d'ajonc d'Europe et les tentatives pour ameliorer sa justesse en utilisant la modelisation par regression ont echoue. Le temps de reponse de la strate aerienne de combustibles legers etait tres rapide (38 a 77 min) et cela a d'importantes repercussions pour la determination du risque d'incendie. L'approche de comptabilite etait la methode la plus prometteuse pour predire la teneur en humidite de la strate aerienne. Il etait par contre impossible de modeliser les conditions meteorologiques a l'echelle des combustibles. Cependant, ce modele merite d'etre davantage valide et etendu a d'autres combustibles arbustifs. Il pourrait aussi etre incorpore dans les systemes existants de determination des risques d'incendie qui peuvent utiliser des donnees meteorologiques prises a toutes les heures. [Traduit par la Redaction], Introduction Fuel moisture influences all aspects of fire behaviour and combustion, including ease of ignition, availability of fuel for combustion, and rates of combustion (Brown and Davis 1973; Pyne et [...]

Abstract. Fire-prone shrub-dominated vegetation communities cover a considerable portion of Australia, including areas fringing urban development. Near urban interfaces, they are actively managed with prescribed fire to reduce the risk of wildfire (unplanned fire). Knowledge of the range of conditions that allow fires to spread or fail to do so is limited and can inconvenience fire managers when conducting prescribed burns. A series of experimental ignitions conducted in miniature shrublands reconstructed in the laboratory were used to investigate factors that influence ignition thresholds. The miniature shrublands were composed of foliage from the shrub Allocasuarina nana and were prepared over a range of moisture contents and densities. The impact of dead fuel within the aerial structure of the shrubs was also investigated, as was the presence and absence of wind and litter. The most important factors for spread initiation were identified using logistic regression analysis and classification tree modelling. The presence of litter, live fuel moisture content, shrub-layer density, presence of wind, and the amount and continuity of the dead elevated fuel were all found to influence spread sustainability. There was a negative interaction between shrub-layer density and live fuel moisture content, showing the effect of density to be less at higher moisture contents. [ABSTRACT FROM AUTHOR]