Fire Danger Meter Research Articles

Existing fire behaviour models under-predict the rate of spread of summer fires in open jarrah (Eucalyptus marginata) forest

SummaryFire behaviour data from Project Vesta experimental fires were used to evaluate the fire behaviour relationship on the Forest Fire Danger Meter (FFDM), the Forest Fire Behaviour Tables (FFBT) for Western Australia and the fire spread model of Burrows (1999) for predicting the rate of spread of fires in jarrah (Eucalyptus marginata) forest under dry summer conditions. Experimental fires were conducted at two sites in south-western Australia under conditions of moderate to high forest fire danger with fine fuel moisture contents of 6–9% oven dry weight and wind speeds up to 20 km h−1 (at 10 m in the open). Fuels ranged in age from 2 to 22 y since the last fire and had understorey shrub layers from 0.5 to 2.0 m tall. Mean rates of spread for experimental fires were 392 m h−1 and 405 m h−1 at the low and tall shrub sites respectively, with the fastest fires spreading at close to 1200 m h−1. Fires spread two to three times faster than predicted by the FFDM and FFBT fire spread models, and up to five times faster than predicted by the spread model of Burrows. Both the FFDM and FFBT models predicted fire spread better at the low shrub fuel site and when wind speeds were <12.5 km h−1. All models under-predicted fire spread at the tall shrub site and grossly under-predicted fire spread when wind speeds were >12.5 km h−1. We argue that existing fire behaviour models under-predict because they were developed using data from fires that had not achieved a quasi-steady rate of spread, whereas the line ignition technique used during Project Vesta experiments resulted in fires travelling at a speed closer to their potential rate of spread for the prevailing conditions. Existing guides remain valid for predicting spread during the early stages of fire growth when fires are developing from a point ignition and the headfire remains narrow.

Biomass burning emissions over northern Australia constrained by aerosol measurements: I—Modelling the distribution of hourly emissions

Emissions of aerosol from biomass burning in northern Australia are globally significant, yet existing estimates of their magnitude are essentially unconstrained by observation. This two-part series (see Part II by Luhar et al. [2008. Biomass burning emissions over northern Australia constrained by aerosol measurements: II—Model validation, and impacts on air quality and radiative forcing. Atmospheric Environment, submitted for publication] seeks to address this by first formulating a scheme to determine the emissions from the Top End region of the Northern Territory during the 2004 burning season at a high temporal and spatial resolution (1 h, 1 km). The emissions are then validated using a meteorological and transport model called TAPM coupled with a variety of field measurements. The high resolution not only enables validation against various meteorological and aerosol data sets, but also allows prediction of local air quality events. Essential inputs to the emission calculations are satellite-based measurements of fire scars, yielding burnt areas, and hotspots, providing timing information on daily basis. It is shown that hotspots without associated fire scars must be taken into account in order to produce credible aerosol fields. Prediction of emissions at hourly time resolution is enabled by assigning a diurnal variation based on a McArthur fire danger meter. The total carbon emission for the 2004 season is computed to be 67.6 Tg, in remarkable agreement with the bulk estimate of 64.3 Tg derived for the Australian National Greenhouse Gas Inventory, and comparable to the figure of 57.0 Tg determined from the Global Fire Emissions Database (GFEDv2). The total PM 2.5 (particulate matter with an aerodynamic diameter of 2.5 μm or less) emission is computed to be 0.67 Tg. The transport modelling shows that emissions leaving the study region are largely advected to the west over the Timor Sea towards the Indonesian archipelago from April to September, shifting to the south-west during October–November where they enhance the aerosol loading over Western Australia.

Comparison of Techniques for Visualising Fire Behaviour

AbstractDuring every Australian summer fires are common in the south‐eastern region of the continent. The combined forces of climate, topography and vegetation make Victoria in particular, one of the most fire prone regions on earth (DSE 2003). Throughout its history, Victoria has seen a number of devastating bushfires, including Black Friday 1939, Ash Wednesday 1983, and more recently in the northeast of the State in 2003. The loss of life combined with the damage caused to land and property results in a heavy cost to the community. In Victoria, two of the organizations involved in fire management are the Victorian Department of Sustainability and Environment (DSE) and the Country Fire Authority (CFA). Both use fire ‘meters’ to determine potential fire behaviour given certain conditions. Values for temperature, wind speed, fuel load and vegetation type are input and a numerical estimate of fire danger given. There are a number of different meters used for different locations and environmental types. The most common meter used in Victoria is the McArthur Meter (CSIR0 2001b). The output data from this meter is numerical, and provides no spatial representation of fire danger. This paper looks at a variety of techniques used to visualise the numerical output from the McArthur Forest Fire Danger Meter. The article outlines the different models used by fire managers to simulate a fire situation, to assess future scenarios and for decision making involving fire management. Particular emphasis is placed on the McArthur Forest Fire Danger Meter as this is commonly used by fire departments in Australia. The article then focuses on geographical visualisation and a number of techniques employed to convey spatial information are discussed. The article then goes on to describe the fire simulation prototypes created for a study, a visualisation proof‐of‐concept product for organizations involved in managing bushfires in Australia. Finally, results from the evaluation of the prototype are presented.

A fuel dryness index for grassland fire-danger assessment

The assessment of fuel moisture content on a large spatial scale requires several observations and estimates and is often time consuming and costly due to labour and transportation expenses. Therefore, various models based on empirical functions of weather variables have been developed and applied to determine the amount of moisture in fuel. In this paper, a fuel dryness index ( F d) based on biophysical principles associated with energy exchange is presented and applied to monitor fuel moisture content for annual grasslands. Daily values of F d were determined as the ratio of sensible heat flux density to the available energy using high-frequency temperature data and the surface renewal (SR) method in combination with net radiation and soil heat flux values. The SR method was evaluated by comparing with sensible and latent heat flux densities from eddy covariance data measured in a fire-vulnerable annual grassland. The F d values and trends were compared with three well-known slow response fire-danger indices including the Keetch–Byram drought index, two modified versions of the drought factor in the McArthur forest fire-danger meter, and the fast response fine fuel moisture code of the Canadian fire weather index. Moreover, F d index was compared with the McArthur grassland fire-danger meter. The F d index was more responsive to daily changes than most of the other indices, providing accurate information on fuel dryness condition of a live vegetation grassland. In addition, it can potentially eliminate the need for calibrated empirical weather models and fuel stick measurements.

Controlling bush fires

With bush fires burning hundreds of thousands of hectares in the populous Australian state of New South Wales, a recent study indicates that a Fire Danger Meter used since the 1960s by firefighters there to predict prescribed fire spread in eucalyptus forests is inaccurate under wildfire conditions.The meter could under‐predict the rate of fire spreading in forests by a factor of 3 or more for extreme fire conditions or when wind speeds are greater than 15 kilometers per hour, according to the report by Project Vesta. The project is a 6‐year endeavor by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO), in collaboration with the Western Australian Department of Conservation and Land Management (CALM), and land management agencies and fire authorities in other Australian states.

Flame residence times and rates of weight loss of eucalypt forest fuel particles

Shape, size, composition and arrangement of fuel particles within a fuel array significantly affect the way in which wildland fires behave. Australian eucalypt forest fire behaviour models characterise fine fuels according to the quantity burnt in the flaming zone, and the upper size limit for fine fuel particles is somewhat arbitrarily set at 6 mm for the McArthur Forest Fire Danger Meter and 10 mm for the Forest Fire Behaviour Tables for Western Australia. Flame residence time and rate of weight loss during combustion of dry eucalypt leaves and different dimensions of round wood were measured to provide a scientific basis for standardising litter fuel sampling in dry eucalypt forests. Eucalypt leaves burnt at a rate equivalent to a piece of 4 mm diameter round wood, with smaller diameter round wood being the most flammable component of the fuel array. Based on flame residence times of individual fuel particles measured in the laboratory, and eucalypt surface fuel arrays observed in the field, fine litter fuel sampling should be standardised to leaves and round wood less than 6 mm in diameter. This study also enables the determination of the contribution of larger fuel particles to flaming zone combustion and intensity.

Improved Formula for the Drought Factor in McArthur's Forest Fire Danger Meter

Summary McArthur's Forest Fire Danger Meter (Mark 5) is a key tool for assessing broadscale fire danger throughout eastern Australia. The Drought Factor, an indicator of the fuel availability as calculated by the meter, is a key input in calculating the Forest Fire Danger Index. The currently accepted analytic method for calculating the Drought Factor is reviewed and shown to give significantly different results to that calculated by McArthur's meter. This paper proposes a new formula for calculating the Drought Factor and shows that it fits McArthur's meter to a far better degree than the previously published formula.

A Qualitative Comparison of Fire Spread Models Incorporating Wind and Slope Effects

Abstract Wind velocity and slope are two critical variables that affect wildland fire rate of spread. The effects of these variables on rate of spread are often combined in rate-of-spread models using vector addition. The various methods used to combine wind and slope effects have seldom been validated or compared due to differences in the models or to lack of data. In this study, rate-of-spread predictions from the Canadian Fire Behavior Prediction (FBP) system, McArthur's Mark V forest fire danger meter, the Rothermel empirical model, and the Pagni and Peterson physical model were compared with spread rates observed in a designed laboratory experiment in which wind velocity and slope were varied. Methods of combining wind and slope developed by Albini, McAlpine, and Rothermel were applied to two forms of Rothermel's model. Rothermel's model (original and modified) coupled with Albini's method and Pagni's model predictions closely reproduced the observed shape of the rate-of-spread response to wind and slope. Rothermel's method and McAlpine's method worked well in all cases except in upslope spread with opposed flow. However, Rothermel's model failed to predict a nonzero rate of spread in fuel beds with moisture contents of 35%. Possible causes of overprediction by McArthur's model and the FBP model included: (1) application of equations derived from full-scale fires to laboratory-scale fires, (2) improper selection of fuel type to represent artificial fuel beds, and (3) inaccurate estimation of wind velocity 10 m above the vegetation surface using a logarithmic profile. For. Sci. 43(2):170-180.

Comparison of grass fuel moisture contents predicted using the McArthur Mark V Grassland Fire Danger Meter and an equation derived from the meter

Summary The moisture content of fully cured grass fuel predicted by the original slide rule version of the McArthur Mark V Grassland Fire Danger Meter may differ by up to 3% in oven dry weight from that predicted for equivalent weather conditions by a commonly used equation derived from the meter. The difference between predicted values from the original meter and the equation is greatest at lower air temperatures (≤ 20°C) and when relative humidity is ≥ 40%. This discrepancy is unlikely to result in substantial differences in calculated fire danger indices, but could affect the results of studies attempting to correlate observed fuel moisture contents with predictions from either the original meter or the equation.

Fire behaviour and fuel reduction burning: Bemm River wildfire, October 1988

Summary On 14 October 1988 a major wildfire occurred in the Bemm River area, 33 km east of Orbost in the East Gippsland region of Victoria. The weather was dominated by wind speeds of gale force strength. The fire burnt under “very high” to “extreme” fire danger conditions with a maximum McArthur fire danger index of 82, a maximum mean forward rate of spread between 3.5 and 4.0 km/h and a maximum mean fireline intensity in the range 31,200 to 35,500 kW/m. The final area of the wildfire was 5,670 ha and the perimeter was 80 km. A highly significant influence on fire behaviour was the layer of aerated, highly flammable shrub fuel. This was combined in the coastal forests of the Bemm River area with high quantities of litter and the high spotting potential of the stringybark eucalypts. Total fine fuel loads averaged about 20 t/ha. The rate of spread predicted by the McArthur Mk 5 Forest Fire Danger Meter during the initial two hour period of the wildfire was 2.0 km/h and the observed mean rate of spread was ...

Assessment of existing fine fuel moisture models applied toEucalyptuslitter

Summary The diurnal trends in dead leaf, bark and twig moisture content on the floor of a Eucalyptus forest in south-eastern Australia were examined over a four day period. Substantial differences were found in moisture content among the three fuel types. At night the twigs remained the driest, while the leaves, through condensation of dew and distillation of moisture from the soil, were the wettest. During the daytime the leaves and bark reached lower fuel moisture minima than the twigs. The adequacy of several fine fuel moisture models was assessed. The locally developed Grassland Fire Danger Meter and Forest Fire Danger Meter together with the Fire Behaviour Officer's model were the best predictors of diurnal fuel moisture content. The usefulness of the timelag concept in Eucalyptus fuels is discussed and the results of the study suggest that modifications should be made to the Fine Fuel Moisture Code and the BEHAVE model for application to these fuels. The need to incorporate a parameterisation of nocturnal condensation into existing models is indicated.

A correction to the equations describing the McArthur forest fire danger meter

AbstractThe addition of a limit to the drought factor used it the equations describing the McArthur forest fire danger meter Mark 5 gives an improved estimation of forest fire behaviour.

ASSESSMENT OF FIRE DANGER CONDITIONS

SUMMARY At the Yallourn and Kiewa undertakings of the State Electricity Commission of Victoria, a simple fire danger meter is being used to assist the fire protection staff in their judgment of fire danger conditions in the surrounding forests. On this meter, the fire danger rating is arrived at by adding a burning index, based on weather conditions on the day, to a season index, based on past weather history for the season. The formulae for calculating these indices are empirical, and are based on a study of recorded weather conditions in relation to actual bush fire and controlled burning history, mainly for the Yallourn area, during the summer seasons from 1938 to 1949. This method of fire danger rating fits past experience over this period, it has been used with reliable results over the past two seasons, and it seems to offer a valuable means whereby the forester can check his judgment of the degree of fire danger and the extent to which fire fighting preparedness needs to over-ride normal forestry a...