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

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. Source

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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