@article {bnh-7343, title = {Effect of weather forecast errors on fire growth model projections}, journal = {International Journal of Wildland Fire}, year = {2020}, month = {08/2020}, abstract = {

Fire management agencies use fire behaviour simulation tools to predict the potential spread of a fire in both risk planning and operationally during wildfires. These models are generally based on underlying empirical or quasi-empirical relations and rarely are uncertainties considered. Little attention has been given to the quality of the input data used during operational fire predictions. We examined the extent to which error in weather forecasts can affect fire simulation results. The study was conducted using data representing the State of Victoria in south-eastern Australia, including grassland and forest conditions. Two fire simulator software packages were used to compare fire growth under observed and forecast weather. We found that error in the weather forecast data significantly altered the predicted size and location of fires. Large errors in wind speed and temperature resulted in an overprediction of fire size, whereas large errors in wind direction resulted in an increased spatial error in the fire{\textquoteright}s location. As the fire weather intensified, fire predictions using forecast weather under predicted fire size, potentially resulting in greater risks to the community. These results highlight the importance of on-ground intelligence during wildfires and the use of ensembles to improve operational fire predictions.

}, keywords = {Bayesian Network, fire prediction, meteorological forecast, sensitivity, simulation}, doi = {https://doi.org/10.1071/WF19199}, url = {https://www.publish.csiro.au/wf/wf19199}, author = {Trent Penman and Dan Ababei and Jane Cawson and Brett Cirulis and Thomas Duff and Swedosh, W and James Hilton} } @conference {bnh-6291, title = {Wind-terrain effects on firebrand dynamics}, booktitle = {23rd International Congress on modelling and Simulation}, year = {2019}, month = {12/2019}, abstract = {

Despite its importance in bushfire propagation, firebrand transport and the spotting process are still poorly understood, and there is no definitive model that can adequately emulate the spotting process in general. The dynamics of firebrands are difficult to predict due to the complex flow structure resulting from the interaction of a buoyant plume with a boundary layer wind field. Understanding the nature of this flow structure, especially for complex terrain, is essential for determining the likely path of firebrands and subsequent distributions of new spot fires and risk levels on structures downwind from the fire.

Although several prior computational modelling studies have carried out investigations of firebrand transport, the effect of the terrain has not previously been taken into account. It is well known that topography can significantly affect ember generation. For example, the enhanced intensity of a fire running up a steep slope can generate a large number of embers. More generally, terrain-modified flows and the strong turbulence associated with leeward slopes and flow around other prominent topographic features may have a pronounced effect on the transport of firebrands. Moreover, modes of dynamic fire propagation such as vorticity-driven lateral spread and eruptive fire spread in canyons involve a coupling between the fire, the terrain and the prevailing winds and so can affect the rate at which firebrands are produced as well as their subsequent transport.

In this study we use a coupled computational fluid dynamic (CFD) and Lagrangian particle approach to model the transport of firebrands. The model is applied to two different terrain scenarios to investigate the flow dynamics, firebrand trajectories and landing patterns resulting from the interaction with the terrain. The first scenario is a line of fire on the lee slope of a ridge burning perpendicular to an incident wind flow. The second scenario is a fire burning in a canyon aligned with the wind. The simulations indicate that the addition of terrain adds a further level of complexity to the flows generated by interaction between the wind and the fire. The terrain appears to modify the counter-rotating vortex pair in the plume structure. For the fire in the lee of the ridge line, the wind-terrain interaction resulted in a flattening and tilting of the counter-rotating vortex pair and enhanced regions of recirculation at the edges of the fire, which were conducive to lateral transport of embers. For the fire in the canyon, the channelling of the winds up the canyon resulted in the formation of a single jet-like vortex transporting firebrands upwards and over the top of the canyon. We hypothesise that this effect is caused by the shape and alignment of the canyon, which forces the vortex pair to merge into a single vortex.

}, keywords = {Climate change, Hydrograph model, parametrization, precipitation, runoff formation processes}, doi = {https://doi.org/10.36334/modsim.2019.H7.hilton}, url = {https://mssanz.org.au/modsim2019/H7/hilton.pdf}, author = {James Hilton and Jason J. Sharples and Garg, N and Murray Rudman and Swedosh, W and Commins, D} } @article {bnh-5192, title = {Incorporating convective feedback in wildfire simulations using pyrogenic potential}, journal = {Environmental Modelling \& Software}, volume = {107}, year = {2018}, month = {09/2018}, pages = {12-24}, chapter = {12}, abstract = {

Modelling the dynamics of wildfires is very computationally challenging. Although three-dimensional\ computational fluid dynamics\ (CFD) models have been successfully applied to wildfires, the\ computational time\ required makes them currently impractical for operational usage. In this study, we develop a two-dimensional\ propagation model\ coupled to a {\textquoteleft}pyrogenic{\textquoteright}\ potential flowformulation representing the inflow of air generated by the fire. This model can accurately replicate features of fires previously unable to be simulated using current\ two-dimensional models, including development of a fire line into a parabolic shape, attraction between nearby fires and the observed closing behaviour of {\textquoteleft}V{\textquoteright} shaped fires. The model is compared to\ experimental resultswith good agreement. The pyrogenic potential model is orders of magnitude faster than a full\ CFD\ model, and could be used for improved operational wildfire prediction.

}, doi = {https://doi.org/10.1016/j.envsoft.2018.05.009}, url = {https://www.sciencedirect.com/science/article/pii/S1364815217309593}, author = {James Hilton and Sullivan, Andrew and Swedosh, W and Jason J. Sharples and Christopher Thomas} } @conference {bnh-5024, title = {Pyroconvective interactions and dynamic fire propagation}, booktitle = {AFAC18}, year = {2018}, month = {09/2018}, address = {Perth}, abstract = {

Modelling the dynamic propagation of wildfires remains a significant challenge. Pyroconvective interactions between the fire and the atmosphere, or between different parts of the fire itself, can produce distinctly non-steady modes of fire propagation that cannot be accounted for using current operational models.


While sophisticated three-dimensional models (e.g. computational fluid dynamics (CFD) models or coupled fire-atmosphere models) have been successfully applied to wildfires, their computational requirements render them impractical for operational usage.


Here we discuss a computationally efficient two-dimensional propagation model, which can accurately replicate dynamic features of fire spread that cannot be simulated using existing two-dimensional models. These features include the development of a wind-driven fire line into a parabolic shape, attraction between nearby fires and the observed closing behaviour of junction fires. The model is compared to experimental results with good agreement.
The model incorporates a simple sub-model to account for the inflow of air generated by a fire, which allows the model to run orders of magnitude faster than full physical models, while still capturing many of the essential features of dynamic fire propagation. We argue that such a model could lead to significant improvements in operational wildfire prediction.
In addition, we will highlight some recent insights in to how the geometry of a fire line and the flaming zone influences development of the pyroconvective plume above a fire. In particular, we present evidence that the geometry of the burning region can affect plume development in a way that is comparable to the effect of total energy release.

}, author = {James Hilton and Badlan, R and Sullivan, Andrew and Swedosh, W and Thomas, C. M. and Jason J. Sharples} }