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Cruz M.G.,CSIRO | Cruz M.G.,Bushfire Cooperative Research Center | Alexander M.E.,Natural Resources Canada | Alexander M.E.,University of Alberta
International Journal of Wildland Fire | Year: 2010

To control and use wildland fires safely and effectively depends on creditable assessments of fire potential, including the propensity for crowning in conifer forests. Simulation studies that use certain fire modelling systems (i.e. NEXUS, FlamMap, FARSITE, FFE-FVS (Fire and Fuels Extension to the Forest Vegetation Simulator), Fuel Management Analyst (FMAPlus®), BehavePlus) based on separate implementations or direct integration of Rothermel's surface and crown rate of fire spread models with Van Wagner's crown fire transition and propagation models are shown to have a significant underprediction bias when used in assessing potential crown fire behaviour in conifer forests of western North America. The principal sources of this underprediction bias are shown to include: (i) incompatible model linkages; (ii) use of surface and crown fire rate of spread models that have an inherent underprediction bias; and (iii) reduction in crown fire rate of spread based on the use of unsubstantiated crown fraction burned functions. The use of uncalibrated custom fuel models to represent surface fuelbeds is a fourth potential source of bias. These sources are described and documented in detail based on comparisons with experimental fire and wildfire observations and on separate analyses of model components. The manner in which the two primary canopy fuel inputs influencing crown fire initiation (i.e. foliar moisture content and canopy base height) is handled in these simulation studies and the meaning of Scott and Reinhardt's two crown fire hazard indices are also critically examined. © 2010 IAWF.


Sharples J.J.,Australian Defence Force Academy | McRae R.H.D.,Bushfire Cooperative Research Center | Wilkes S.R.,Fire Management Unit
International Journal of Wildland Fire | Year: 2012

The interaction of wind, terrain and a fire burning in a landscape can produce a variety of unusual yet significant effects on fire propagation. One such example, in which a fire exhibits rapid spread in a direction transverse to the synoptic winds as well as in the usual downwind direction, is considered in this paper. This type of fire spread, which is referred to as 'fire channelling', is characterised by intense lateral and downwind spotting and production of extensive flaming zones. The dependence of fire channelling on wind and terrain is analysed using wind, terrain and multispectral fire data collected during the January 2003 Alpine fires over south-eastern Australia. As part of the analysis, a simple terrain-filter model is utilised to confirm a quantitative link between instances of fire channelling and parts of the terrain that are sufficiently steep and lee-facing. By appealing to the theory of windterrain interaction and the available evidence, several processes that could produce the atypical fire spread are considered and some discounted. Based on the processes that could not be discounted, and a previous analysis of wind regimes in rugged terrain, a likely explanation for the fire channelling phenomenon is hypothesised. Implications of fire channelling for bushfire risk management are also discussed. © 2012 IAWF.


Adams M.A.,University of Sydney | Adams M.A.,Bushfire Cooperative Research Center
Forest Ecology and Management | Year: 2013

Global evidence posits that we are on the cusp of fire-driven 'tipping points' in some of the world's most important woody biomes including savannah woodlands, temperate forests, and boreal forests, with consequences of major changes in species dominance and vegetation type. The evidence also suggests that mega-fires are positive feedbacks to changing climates via carbon emissions, and will be responsible for large swings in water yield and quality from temperate forests at the regional scale.Two factors widely considered to have contributed to our current proximity to tipping points are changing climates and human management - the latter most obviously taking the form of allowing fuels to build up, either through policies of fire suppression or failure to implement sufficient fuel reduction fires - to the point where wildfire intensity increases dramatically. Much of the evidence comes from Australia and the USA, but domains such as Africa and the boreal north provide additional insights.Forests adapted to regimes of low-moderate intensity fires may not face the same challenges as the iconic ash forests of Australia and the coniferous forests of Yellowstone or the west coast of the USA that are adapted to high intensity fire. However the often modest physical barriers (including distance, topography and climate) between forests adapted to more frequent, low-moderate intensity fires on the one hand, and less frequent, high intensity fires on the other, are easily overcome by confluences of continually increasing fuel loads and changing climates that serve to increase both fire frequency and intensity.For temperate forests, we can mitigate the extent of large-scale, high intensity fires and their consequences if we carefully use fuel reduction fires and other standard forest management practises such as thinning. Mitigation will require assessing impacts on biodiversity of smaller, low-intensity fires at intervals of 5-10. years (to reduce fuels and mitigate fire size and intensity), against those of large-scale, high intensity wildfires at increasing (but unknown) frequency. Mitigation will require that forests be managed contiguously, not via different agencies with different objectives according to land tenure. Managing requires that governments and the communities they serve acknowledge the limitations of fire-suppression. Mitigating the incidence and effects of large-scale, high intensity fires through embracing the use of managed fire in conjunction with judicious use of fire suppression offers opportunity to avoid potentially large changes in vegetation and biomass (e.g. abundance of dominant species, biodiversity, fuel structure and loads), as well as in water yield and quality and carbon carrying capacity. © 2012 Elsevier B.V.


Possell M.,University of Sydney | Possell M.,Bushfire Cooperative Research Center | Bell T.L.,University of Sydney
International Journal of Wildland Fire | Year: 2013

Leaves from three species of Eucalyptus were combusted in a mass-loss calorimeter to characterise the effect of fuel moisture on energy release and combustion products for this genus. Increasing moisture content reduced peak heat release and the effective heat of combustion in a negative exponential pattern while simultaneously increasing time-to-ignition. Estimates of the probability of ignition, based upon time-to-ignition data, indicated that the critical fuel moisture content for a 50% probability of ignition ranged from 81 to 89% on a dry-weight basis. The modified combustion efficiency of leaves (the ratio of CO2 concentration to the sum of the CO2 and CO concentrations) decreased exponentially as fuel moisture increased. This was because CO2 concentrations during combustion declined exponentially while CO concentrations increased exponentially. However, CO2 mixing ratios were always greater by at least one order of magnitude. Emission factors for CO2 declined exponentially with increasing fuel moisture content while CO emission factors increased exponentially to a maximum. The emission factors for volatile organic compounds increased in a pattern similar to that for CO with increasing fuel moisture content. The empirical relationships identified in this study have implications for fire-behaviour modelling and assessing the effect of fire on air quality and climate. © 2013 IAWF.


Cruz M.G.,CSIRO | Cruz M.G.,Bushfire Cooperative Research Center | Alexander M.E.,University of Alberta
Environmental Modelling and Software | Year: 2013

The degree of accuracy in model predictions of rate of spread in wildland fires is dependent on the model's applicability to a given situation, the validity of the model's relationships, and the reliability of the model input data. On the basis of a compilation of 49 fire spread model evaluation datasets involving 1278 observations in seven different fuel type groups, the limits on the predictability of current operational models are examined. Only 3% of the predictions (i.e. 35 out of 1278) were considered to be exact predictions according to the criteria used in this study. Mean percent error varied between 20 and 310% and was homogeneous across fuel type groups. Slightly more than half of the evaluation datasets had mean errors between 51 and 75%. Under-prediction bias was prevalent in 75% of the 49 datasets analysed. A case is made for suggesting that a ±35% error interval (i.e. approximately one standard deviation) would constitute a reasonable standard for model performance in predicting a wildland fire's forward or heading rate of spread. We also found that empirical-based fire behaviour models developed from a solid foundation of field observations and well accepted functional forms adequately predicted rates of fire spread far outside of the bounds of the original dataset used in their development. © 2013.


Cruz M.G.,CSIRO | Cruz M.G.,Bushfire Cooperative Research Center
International Journal of Wildland Fire | Year: 2010

The operational prediction of fire spread to support fire management operations relies on a deterministic approach where a single 'best-guess' forecast is produced from the best estimate of the environmental conditions driving the fire. Although fire can be considered a phenomenon of low predictability and the estimation of input conditions for fire behaviour models is fraught with uncertainty, no error component is associated with these forecasts. At best, users will derive an uncertainty bound to the model outputs based on their own personal experience. A simple ensemble method that considers the uncertainty in the estimation of model input values and Monte Carlo sampling was applied with a grassland fire-spread model to produce a probability density function of rate of spread. This probability density function was then used to describe the uncertainty in the fire behaviour prediction and to produce probability-based outputs. The method was applied to a grassland wildfire case study dataset. The ensemble method did not improve the general statistics describing model fit but provided complementary information describing the uncertainty associated with the predictions and a probabilistic output for the occurrence of threshold levels of fire behaviour. © 2010 IAWF.


Pfautsch S.,University of Sydney | Pfautsch S.,University of Western Sydney | Adams M.A.,University of Sydney | Adams M.A.,Bushfire Cooperative Research Center
Oecologia | Year: 2013

Making predictions as to how heatwaves will affect forests in the future is a major challenge in ecosystem science, not the least because we have few documented examples of how they respond now. We captured the effects of drought and a record-breaking heatwave on whole-tree water use (Q) in Eucalyptus regnans during the summer drought of 2008/2009 in southeastern Australia. While air temperatures steadily increased, average maximum sap flow (J Smax) declined with progression of the drought prior to the heatwave. In the period approaching the heatwave, Q during daytime (Q d) steadily declined, while nighttime Q (Q n) increased. This pattern was particularly pronounced during nights that followed hot days (>32 °C) where Q n was frequently 20-30 % of Q d. We found clear trends in the relation of Q d to Q n that point to the increasing importance of refilling depleted stem water stores following hot days. On the day the heatwave climaxed (7 February 2009), sap flow (J S) was dramatically low, and declined as weather conditions became increasingly arid (air temperature > 42 °C, vapor pressure deficit >7 kPa). Almost immediately after the heatwave passed J S resumed its common diurnal hysteresis, albeit at slightly slower rates. In the context of prognosticated effects of future climate, our data highlight that depletion and refill of stored water in E. regnans are likely important features for the tree to endure drought- and heat-related climatic extremes. We suggest that elucidating the peculiarity of capacitance and defining its threshold for keystone tree species, such as E. regnans, can add to our understanding of how climatic extremes may affect forests. © 2012 Springer-Verlag Berlin Heidelberg.


Dowdy A.J.,Center for Australian Weather and Climate Research | Mills G.A.,Bushfire Cooperative Research Center
Journal of Applied Meteorology and Climatology | Year: 2012

Asystematic examination is presented of the relationship between lightning occurrence and fires attributed to lightning ignitions. Lightning occurrence data are matched to a database of fires attributed to lightning ignition over southeastern Australia and are compared with atmospheric and fuel characteristics at the time of the lightning occurrence. Factors influencing the chance of fire per lightning stroke are examined, including the influence of fuel moisture and weather parameters, as well as seasonal and diurnal variations. The fuel moisture parameters of the Canadian Fire Weather Index System are found to be useful in indicating whether a fire will occur, given the occurrence of lightning. The occurrence of "dry lightning"(i.e., lightning that occurs without significant rainfall) is found to have a large influence on the chance of fire per lightning stroke. Through comparison of the results presented here with the results of studies from other parts of the world, a considerable degree of universality is shown to exist in the characteristics of lightning fires and the atmospheric conditions associated with them, suggesting the potential for these results to be applied more widely than just in the area of the study. © 2012 American Meteorological Society.


Oneill S.J.,University of Melbourne | Handmer J.,RMIT University | Handmer J.,Bushfire Cooperative Research Center
Environmental Research Letters | Year: 2012

The 2009 Black Saturday bushfires led to 172 civilian deaths, and were proclaimed as one of Australias worst natural disasters. The Victorian Bushfires Royal Commission was set up in the wake of the fires to investigate the circumstances surrounding the death of each fatality. Here, results from an analysis undertaken for the Commission to examine the household preparedness policy Prepare, Stay and Defend, or Leave Early (Stay or Go), plus an examination of the Commissions recommendations, are explored in the broader context of adaptation to bushfire. We find Victoria ill adapted to complex bushfire risk events like Black Saturday due to changing settlement patterns and the known vulnerabilities of populations living in fire prone areas, and increasingly in the future due to the influence of climate change extending fire seasons and their severity. We suggest that uncertainty needs to be better acknowledged and managed in fire risk situations, and that the responsibility for fire preparedness should be more justly distributed. We suggest that a transformation in adaptation is required to effectively manage complex bushfire risk events like Black Saturday, and provide four key ways in which transformation in bushfire preparedness could be achieved. © 2012 IOP Publishing Ltd.


Buckley T.N.,Sonoma State University | Buckley T.N.,Bushfire Cooperative Research Center | Adams M.A.,Bushfire Cooperative Research Center | Adams M.A.,University of Sydney
Plant, Cell and Environment | Year: 2011

Leaf respiration continues in the light but at a reduced rate. This inhibition is highly variable, and the mechanisms are poorly known, partly due to the lack of a formal model that can generate testable hypotheses. We derived an analytical model for non-photorespiratory CO2 release by solving steady-state supply/demand equations for ATP, NADH and NADPH, coupled to a widely used photosynthesis model. We used this model to evaluate causes for suppression of respiration by light. The model agrees with many observations, including highly variable suppression at saturating light, greater suppression in mature leaves, reduced assimilatory quotient (ratio of net CO2 and O2 exchange) concurrent with nitrate reduction and a Kok effect (discrete change in quantum yield at low light). The model predicts engagement of non-phosphorylating pathways at moderate to high light, or concurrent with processes that yield ATP and NADH, such as fatty acid or terpenoid synthesis. Suppression of respiration is governed largely by photosynthetic adenylate balance, although photorespiratory NADH may contribute at sub-saturating light. Key questions include the precise diel variation of anabolism and the ATP: 2e- ratio for photophosphorylation. Our model can focus experimental research and is a step towards a fully process-based model of CO2 exchange. © 2010 Blackwell Publishing Ltd.

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