Dynamic development of the 2013 Aberfeldy fire

It was held jointly with the 23rd National Conference of the Australian Society for Operations Research and the DSTO led Defence Operations Research Symposium (DORS 2015).The 2013 Aberfeldy fire, in eastern Victoria, exhibited unexpectedly rapid fire spread after its ignition on 17 January. In the first 16 hours after ignition at around 11: 30am, the fire spread approximately 30 kilometres towards the southeast and burned 20,000 hectares. Much of this rapid fire spread occurred at night. Also of significance was that the fire burnt in complex topography, with slopes greater than 20., and that in a number of instances the fire exhibited lateral spread; that is, spread in a direction almost perpendicular to the prevailing wind direction. In this paper we consider the development of the 2013 Aberfeldy fire in light of a number of recent insights into the dynamic behaviour of fires burning in rugged terrain under strong winds. In particular, we draw on findings that initially related to the 2003 Canberra fires to explain the occurrence of the lateral spread. More recent numerical and experimental work will also be discussed in this context. The observed development of the fire is also considered in the context of the traditional fire spread modelling approach, whereby the fire is assumed to propagate at a quasi-steady rate of spread modulated by the combined effects of wind and terrain. In particular, vector fields representing the expected rate and direction of fire spread are derived using traditional methods and are applied across the fire affected landscape. Infrared linescans, showing the development of the fire at several junctures in time, exhibit fire propagation patterns that are difficult to reconcile with the rate of spread vector fields at several key locations. Specifically, the development of the fire into narrow fingers propagating laterally across the tops of slopes in the immediate lee of a ridge line do not match with the predictions derived from traditional quasi-steady fire propagation models. This pattern of fire spread does however match quite well with that shown to occur when fires are affected by vorticity-driven lateral spread (VLS). The VLS phenomenon arises due to a three-way interaction between strong winds, steep terrain and a significant fire in the landscape. Analysis of the Aberfeldy fire showed that the observed spread adhered to VLS occurrence thresholds established through consideration of other notable fires, and through numerical modelling and experimental analysis. The strong pyroconvection and pattern of smoke observed in association with lateral spread events in the Aberfeldy fire were also consistent with that observed in other confirmed VLS events. The findings of this case study indicate that there were readily identifiable dynamic processes that drove the development of the Aberfeldy fire. These processes were essentially the same as those that drove the development of the 2003 Canberra fires and a number of significant fires in the ensuing years. The findings further suggest that research into the dynamic drivers of extreme bushfires, which now spans about 10 years, can offer significant improvements in the way such fires are modelled operationally. Some suggestions about how these improvements could be implemented within the working environment of a Fire Behaviour Analyst are offered.R. Quill, J. J. Sharple

A rate of spread index for fires in spinifex fuels

Fires in spinifex occur throughout arid and semi-arid parts of Australia and in some cases can affect large tracts of the landscape with associated environmental impacts. In response to this environmental challenge an empirical model for the prediction of fire spread rate in spinifex fuels has recently been developed, based on a number of experimental burns conducted in Western Australia. In other research related to fires in grasslands, a simple rate of spread index for quasi-equilibrium fire spread was developed and, despite its simplicity, was shown to provide practically identical output to current operational grassland fire spread prediction models. This simple rate of spread index for grasslands conceptualises the rate of fire spread as wind speed divided by fuel moisture content, where fuel moisture content is estimated using a fuel moisture index (FMI). Such a conceptualisation embodies the notion that fires will spread faster in windier conditions and in fuels that are drier. The rate of spread index, as it applied to grassfires, also incorporates a term that accounts for an intensity-dependent indraft that counters the prevailing winds at the fire line. As such, the rate of spread index can be viewed as a two parameter model for quasi-equilibrium fire sprea

Lifespan theorem for constrained surface diffusion flows

We consider closed immersed hypersurfaces in $\R^{3}$ and $\R^4$ evolving by a class of constrained surface diffusion flows. Our result, similar to earlier results for the Willmore flow, gives both a positive lower bound on the time for which a smooth solution exists, and a small upper bound on a power of the total curvature during this time. By phrasing the theorem in terms of the concentration of curvature in the initial surface, our result holds for very general initial data and has applications to further development in asymptotic analysis for these flows.Comment: 29 pages. arXiv admin note: substantial text overlap with arXiv:1201.657

Natural resource risk and cost management in environmental restoration: Demonstration project at the Savannah River Site

The US Department of Energy (DOE) is both a trustee for the natural resources present on its properties and the lead response agency under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). As such, DOE is addressing the destruction or loss of those resources caused by releases of hazardous substances from its facilities (DOE 1991) and collecting data to be used in determining the extent of contamination at its facilities, estimating risks to human health and the environment, and selecting appropriate remedial actions. The remedial investigation/feasibility study (RI/FS) process is used to investigate sites and select remedial actions. A Natural Resource Damage Assessment (NRDA) process may be used to determine whether natural resources have also been injured by the released hazardous substances and to calculate compensatory monetary damages to be used to restore the natural resources. In FY 1994, the Savannah River Site (SRS) was chosen to serve as a demonstration site for testing the integrated NRDA framework and demonstrating how NRDA concerns might be integrated into the environmental restoration activities of an actual site that is characteristically large and complex. The demonstration project (1) provided a means to illustrate the use of complex analyses using real information on the specific natural resources of the SRS; (2) served as a vehicle for reinforcing and expanding the SRS staff`s understanding of the links between the NRDA and RI/FS processes; (3) provided a forum for the discussion of strategic issues with SRS personnel; and (4) allowed the refining and elaboration of DOE guidance by benchmarking the theoretical process using real information and issues

A statistical approach to understanding canopy winds over complex terrain

Winds that flow within a forest canopy in complex terrain exhibit considerable variability that can have significant consequences for environmental processes such as the spread of bushfires, seed dispersal and transport of pollutants. This variability is still poorly understood, due in part to limited observations of canopy winds over complex terrain, and as such is often unaccounted for in deterministic modelling approaches. Probabilistic representation of wind fields can better characterise variability and build understanding of uncertainty in applications such as bushfire prediction. This study introduces two new, publicly available, datasets that support analyses of canopy winds over complex terrain using novel statistical approaches. Wind fields are characterised using bivariate distributions, representing the response of synoptic winds to changing landscapes, including post-bushfire forest regrowth and varying topography across uniform vegetation. For statistical comparison, non-parametric Kolmogorov-Smirnov style tests are considered. A new test is proposed for the comparison of bivariate circular distributions arising from analyses of wind direction. The study broadly reaffirms established theory while highlighting the variability of canopy winds over complex terrain and the importance of developing statistical techniques that result in a better quantitative understanding of these wind fields and the processes driving them.R. Quill, J. J. Sharples and L. A. Sidh

Observations of the spring-neap modulation of the gravitational circulation in a partially mixed estuary

The long-term variability of the non-tidal circulation in Southampton Water, a partially mixed estuary, was investigated using 71-day acoustic Doppler current profiler (ADCP) time series. The data show evidence that the spring-neap tidal variability of the turbulent mixing modulates the strength of the non-tidal residual circulation, with subtidal neap tide surface flows reaching 0.12 m s-1compared to <0.05 m s-1at spring tides. The amplitude of the neap-tide events in this non-tidal circulation is shown to be related to a critical value of the tidal currents, illustrating the strong dependence on tidal mixing. The results suggest that the dominant mechanism for generating these neap-tide circulation events is the baroclinic forcing of the horizontal density gradient, rather than barotropic forcing associated with ebb-induced periodic stratification. While tidal turbulence is thought to be the dominant control on this gravitational circulation, there is evidence of the additional effect of wind-driven mixing, including the effects of wind fetch and possibly wave development with along-estuary winds being more efficient at mixing the estuary than across-estuary winds. Rapid changes in atmospheric pressure also coincided with fluctuations in the gravitational circulation. The observed subtidal flows are shown to be capable of rapidly flushing buoyant material out of the estuary and into the coastal sea at neap tides

Edge effects on between-fire interval in landscape fragments such as fire-prone terrestrial conservation reserves

When a parcel of land, a reserve, is isolated from its fire-prone landscape context, its fire interval can potentially be altered simply due to diminished access to external fire. A model is developed to depict this situation. Cutting off the external access of randomly-oriented fires along an infinite edge reduces the proportion burnt per year at the edge to one half; the average interval doubles there. Well away from the edge, the fire interval remains the same as it was before fragmentation. When very long strips from which external fires are cut off from both sides are considered, edge effects from the two sides overlap internally such that the average interval between fires in the strip, overall, increases. Overlap increases as width decreases. The same phenomenon occurs in a modelled circular, or other shaped, reserve with the central area being the least affected. Modelled results, expressed as average interval per reserve, were consistent with changes in fire interval in fragments of different size in a mallee-vegetation complex of the wheat belt of south-western Western Australia. Such effects would be at a maximum in small irregularly-shaped reserves. If historical fire regimes are to be maintained for biodiversity conservation purposes, then management intervention will be necessary where this effect occurs

A simple method for assessing fuel moisture content and fire danger rating

The flammability of wildland vegetation is strongly dependent upon the moisture content of fine dead fuels. Consequently, assessing the moisture content of these fuels to within a reasonable degree of accuracy is an important part of wildland fire management. Estimates of fine fuel moisture content can also be combined with information on wind speed, vegetation type and drought effects to provide a measure of fire potential or fire danger rating. For example, the moisture content of eucalypt litter is an important consideration in determining fire danger rating in the forests of southeastern Australia. This paper describes a simple and intuitive linear index, which provides an equivalent measure of the moisture content of eucalypt litter. Despite its simplicity, the so-called fuel moisture index, defined as FMI = 10-0.25(T-H), where T is temperature and H is relative humidity, is shown to be remarkably effective at reproducing the results of a more sophisticated model for the moisture content of eucalypt litter. In previous work the fuel moisture index was combined with information on wind speed U to provide a simple fire danger index F. Under the restrictive assumption of constant fuel availability, F was shown to compare favourably with other measures of fire danger rating that feature in the literature. In this paper we extend the definition of F to incorporate the effects of variable fuel availability. This is done very simply by multiplying F by the drought factor to obtain the index FD. The drought factor, which is determined through knowledge of antecedent rainfall, is used to describe fuel availability in forest fuel types. The utility of the index FD is tested by comparing its value with the McArthur Mark 5 Forest Fire Danger Index (FFDI) using data from two automatic weather stations. Moreover, by converting grass curing, which is used to describe fuel availability in grassland fuels, to an equivalent drought factor the index FD is also compared with the McArthur Mark 4 Grassland Fire Danger Index (GFDI). The comparisons indicate that FD provides a plausible measure of fire danger rating for forest fuels and grassland fuels in particular. The structure of the two McArthur indices with respect to the fuel moisture index is also investigated. It is shown that when viewed in terms of the (FMI, U) phase plane, the McArthur indices have a very simple geometric characterisation: constant FFDI corresponds to straight lines and constant GFDI corresponds to cubic curves in the (FMI, U) plane. This confirms that FMI is a unifying variable which permits a simpler conceptualisation of fire danger rating, at least as it is treated in the McArthur schemes. Hence, characterising fire danger rating in terms of FMI could have a pedagogical advantage over other methods and could provide fire management personnel with a simpler and more intuitive method for assessing fire potential

A simple index for assessing fire danger rating

Fire danger rating systems are used to assess the potential for bushfire occurrence, fire spread and difficulty of fire suppression. Typically, fire danger rating systems combine meteorological information with estimates of the moisture content of the fuel to produce a fire danger index. Fire danger indices are used to declare fire bans and to schedule prescribed burns, among other applications. In this paper a simple fire danger index F that is intuitive and easy to calculate is introduced and compared to a number of fire danger indices pertaining to different fuel types that are used in an operational setting in Australia and the United States. The comparisons suggest that F provides a plausible measure of fire danger rating and that it may be a useful pedagogical tool in the context of fire danger and fire weather

A simple index for assessing fuel moisture content

Assessing fuel moisture content to within a reasonable degree of accuracy is an important part of wildland fire management. In this paper we introduce a fuel moisture index that provides a simple and intuitive method for assessing fuel moisture content. The method can be quickly and easily applied in a field setting to provide a dimensionless measure of fuel moisture content. We compare the index with predictions from several models for fuel moisture content and conclude that it provides an equivalent measure of fuel moisture content for a number of fuel types. We go on to briefly discuss how the index could be used to construct a simple and intuitive fire danger index