@article {bnh-8318, title = {Improved predictions of severe weather to reduce community impact {\textendash} final project report}, number = {721}, year = {2022}, month = {02/2022}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Extreme weather often occurs at relatively small scales.\  Accurate forecasts and understanding of such small-scale processes require high-resolution modelling.\  Forecasts are especially useful in severe weather events, since they play an essential role in allowing communities, industry and emergency services to prepare for and mitigate the impacts. Because forecasts are inherently uncertain in the severity, location and duration of an event, preparation needs to be more widespread than the eventual impact {\textendash} but this over-preparation comes at a cost.\  Detailed prediction of the probabilities of severe impacts would avoid the risk of failing to alert areas with the chance of an impact, while minimising the cost of over-warning.\ 

This project has studied the dynamics, predictability, and processes of severe weather, including fire weather, with the purpose of understanding phenomena with severe impact, improving forecasts of severe weather, and better depicting forecast uncertainty in these events. These goals help facilitate better risk management, improve user preparation, reduce adverse outcomes, and enable more effective mitigation.

The project has featured two main strands.

The first strand comprised case studies of severe weather events. For these, we have combined high-resolution numerical weather prediction (NWP) with a wide range of in situ and remotely sensed observations, to better understand both the high-impact event in question, and other events of that class. All except one of the studies used a version of the Bureau{\textquoteright}s operational NWP system, ACCESS. The events comprised two severe mid-latitude systems (an east coast low, and a severe thunderstorm and tornado outbreak), two severe fires, and a tropical cyclone, thereby covering the gamut of severe weather in Australia. Two of the studies featured ensemble simulation, with the east coast low case being the first time that ensemble ACCESS had been run at this resolution within the Bureau and foreshadowing the Bureau{\textquoteright}s new operational ensemble capability. Each case discovered important fine-scale features that contributed to the severity of the event, advancing our knowledge base and ability to respond.

The second strand studied two important phenomena associated with bushfire plumes: the formation of pyrocumulus clouds and ember transport. In each case, we began with idealised, high-resolution simulations of plumes using a large-eddy model. We used this technology, in which the model is run on a 50-m grid, to capture the most energetic size range of the turbulent eddies that are prominent in fire plumes. We found that the mean travel distance of firebrands depends mainly on wind speed and fire intensity, but the spread in the landing positions shifts from being substantially crosswind at light winds, to dominantly along-wind at high winds. This spread is greatly increased by the turbulence in the plume, and the maximum spotting distance can be more than double the mean for this reason.

We also used our plume modelling to study pyrocumulus clouds and analysed the processes that lead to pyrocumulus, with special attention on the relative importance of moisture from two sources, the atmosphere and combustion, and showed that the latter is negligible except in very dry environments. This somewhat controversial result has been confirmed by a conceptual study of the thermodynamics of pyrocumulus formation.

These initial studies laid a firm theoretical framework for our subsequent development of tools to provide predictions in a form, and at a speed, that is suitable for operational use.

For moist pyroconvection, we developed a paradigm to combine the necessary meteorological and fire information, the pyrocumulonimbus firepower threshold, or PFT. The PFT is defined as the power output from a fire at which pyroCb will begin to form and depends solely on meteorological parameters. Fires hotter than the PFT will initiate pyroCb, according to this paradigm, and cooler fires do not. We also developed a way of computing an approximate PFT from either NWP or observed data and tested this in real time during the extraordinarily severe 2019-20 fire season. The results of that trial were outstandingly successful, with nearly all the 30-odd events being captured, and the forecast guidance for non-events was also reported to have been extremely valuable. The Bushfire and Natural Hazards CRC have provided us with utilisation funding to take this tool another step closer to operational use. The tool has also attracted significant international interest, particularly given the recent spate of events in the USA. We have begun a utilisation project to take the PFT work further, detailed in this report.

For ember transport, we developed a simple model to predict plume-dominated transport, incorporating well-known plume modelling concepts, a model of plume turbulence, and a probabilistic model of ember transport within and beneath the plume. The results agree well with our large eddy-based simulations. This model was coupled to CSIRO{\textquoteright}s Spark fire-spread model and tested on the Kilmore East fire of Black Saturday with excellent results. The combination with Spark will make this tool suitable for future operational use, and the ember transport model could also, of course, be coupled to other fire spread simulators, including the coupled fire-atmosphere model ACCESS-Fire. Working with CSIRO and AFAC, we are putting the necessary things in place to be able to convert the prototype implementation of the ember transport parameterisation in Spark, into an operationally robust and supported system. This will both facilitate further research, and provide the framework to allow users to learn, understand and apply the system.

The value of case studies has been reinforced by our being asked to undertake five case studies of severe fires from the 2019-20 summer. This work will be done jointly with our colleagues from the CRC Coupled fire-atmosphere modelling project, who further developed the ACCESS-Fire model. We expect that this work will provide an impetus to further develop and streamline that capability.

We are also very excited about the potential of the PFT and ember transport tools. While both are relatively early in their development, with the PFT being the more mature, each is presently producing very encouraging results. We are also very conscious that each is raising further scientific questions as they address others, and that both are at the beginning of a steep development and refinement curve that we expect will further improve their accuracy and utility. We are confident that further scientific investment will yield substantial dividends.

}, keywords = {community, Impact, prediction, severe, weather}, issn = {721}, author = {Jeffrey Kepert and KJ Tory and Ching, Eng and Robert Fawcett and Serena Schroeter and W. Thurston and David Wilke and Dragana Zovko-Rajak} } @article {bnh-7900, title = {Coupled fire-atmosphere modelling {\textendash} final project report}, number = {650}, year = {2021}, month = {03/2021}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

This project aims to improve understanding of fire and atmosphere interactions and feedback processes through running the coupled fire-atmosphere model ACCESS-Fire.

Project deliverables include: preparation of meteorological and simulation case studies of significant fire events as publications; installation and testing of the ACCESS-Fire coupled model on the National Computing Infrastructure (NCI); and preparation of training material to support operational implementation of research findings.

The project started in March 2016, and progress over the past four years has delivered across several activities:

The project has demonstrably achieved the objective of building and sharing national capability in fire research and has provided fire and meteorology expertise during high impact events in support of end-users inside their operational centers.\  That outcome is not a specific project deliverable and is to some degree intangible, so not as easily measured as outcomes such as publications.\  However, it successfully realises the CRC objective of building collaborations and trusted partnerships and strengthening national capability. The operational support capability is recognised and valued across fire and land management agencies and in the Bureau.

To complete the project we will finalise publication of the draft papers to ensure that our key findings are documented in the scientific literature; this will expand the international body of knowledge from coupled modelling studies.\ 

We are pleased to bring the project to completion and are gratified that along the way we have shared a valuable legacy of knowledge on fire and atmosphere interactions.\  We have also delivered an important capability in ACCESS-Fire that can provide ongoing benefit to the field of meteorology and fire prediction and to the Australian community into the future.

In the coming months we will continue our conversations with partners and end-users to establish plans for future use and development of ACCESS-Fire as the BNHCRC transitions to the new Disaster Resilience Research Institute.\ \  ACCESS-Fire is an important research tool and has the potential to be a critical operational tool. It will assist in informing fire management decisions as we face increasingly hazardous scenarios in a changing climate.

}, keywords = {coupled, fire-atmosphere, modelling}, issn = {650}, author = {Mika Peace and Jeffrey Kepert and Harvey Ye and Jesse Greenslade} } @article {bnh-8253, title = {Coupled fire-atmosphere simulations of five Black Summer fires using the ACCESS-Fire model - Black Summer final report}, number = {705}, year = {2021}, month = {05/2021}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Context

This research builds on previous work completed during the Coupled fire-atmosphere modelling ACCESS-Fire project, by conducting case studies of five major bushfires that occurred across Australia during the 2019-20 summer. The previous work provided valuable insights into the drivers of periods of extreme fire behaviour associated with the Waroona fire in WA, and the Sir Ivan fire in NSW.

The main objectives of this project are: to investigate the meteorological drivers of extreme fire behaviour at five further fire events; to further test the reliability and stability of the model in different environments across Australia; and to support and share learnings from the events of the 2019-20 summer with partner agencies.

The fire events nominated by state jurisdictions for investigation were: Badja Forest (New South Wales), Stanthorpe (Queensland), Green Valley Talmalmo/Corryong\ (NSW/Victoria), Kangaroo Island (South Australia); and Yanchep (Western Australia).

The case studies show that the local context for each fire is important. Each of the fires posed significant challenges in different ways. In the heavily forested areas of NSW and Victoria, the sheer size, intensity, and duration of the fires were distinctive. At other fires, the proximity of local communities and infrastructure posed serious challenges. All fires were active in the overnight period when conventional fire danger indices typically suggest a decrease in fire activity.

The marine boundary layer, local coastal effects and topography combined to generate complex wind flows that influenced the progression of the Kangaroo Island fire. We also studied the way in which the sea breeze circulation interacted with the Yanchep fire, and examined the impact of a prescribed burn on the rate and direction of spread of the Stanthorpe fire under extreme fire weather conditions.

This project has explored gaps in knowledge and understanding of the processes at play during these unusual events by using the Bureau{\textquoteright}s ACCESS-Fire model to examine the local three-dimensional interactions between the fires and the atmosphere. The learnings from this project may be applied to shape future fire weather products and services.

Method

Based on discussions with our partners in fire agencies, together with documents (including photographs and video) and information on fire spread, fuel types and fuel moisture and atypical fire behaviour, we have run a series of simulations and prepared case study chapters for each of the five fires.

The ACCESS-Fire model was initialised using information provided by fire agencies on ignition location or fire line perimeter and fuel type and availability. Several simulations were conducted for each of the fires, with a focus on different time periods of interest and using updated fire polygon boundaries based on available line scan imagery.

The model configuration does not permit the simulations to account for suppression activities by fire agencies, changes in fuel types on the urban interface, or the impact of roads or other fire breaks in reducing the rate of spread of the fire. Another limitation is that the simulations are a single realisation, when in reality, consideration of forecast uncertainty (for example through running an ensemble scheme) would capture a range of potential outcomes.\ 

Learnings from the case studies reinforce and refine some previous learnings from historical fire events and uncover some new insights into the processes driving the periods of unusual fire behaviour that were observed during the 2019/20 season.

Key findings

The case study analyses have provided valuable insights into meteorological aspects of observed extreme fire behaviour during the 2019/20 summer. Key findings for each of the five case studies are included in the individual chapters for each fire and a synthesis is provided here.\ 

The ACCESS-Fire simulations run at 300 m spatial resolution show that some of the most dangerous effects of the fires, in particular damaging and destructive winds, are fire driven and therefore very localised at a much finer scale than current fire weather products.

The depth, elevation and structure of low-level jets over topography was a critical driver of overnight fire activity.\  Given that these jets are driven by larger scale processes (typically synoptic scale), there is an opportunity to develop new tools based on numerical weather prediction output that highlight the location and intensity of these features. Such tools would provide additional information for meteorologists and FBANs on the strength and height of representative winds for input to two-dimensional fire spread models and could be used to alert fire managers to the risk of atypical fire spread in the overnight period.

A key theme that emerged from the case studies and discussions with stakeholders was the consistent occurrence of heatwaves and their influence on boundary layer structure overnight and on inhibiting fuel moisture recovery during the overnight period. Further research quantifying the effects of overnight heatwaves is required to appropriately plan for the increased risk to communities and fire crews in a changing climate, as the frequency of elevated overnight temperatures has increased over the last few decades and is projected to increase further (along with other factors influencing fire activity).\ \ 

Deep moist pyroconvection producing pyrocumulus (pyroCu) or pyrocumulonimbus (pyroCb) clouds was a feature of the 2019-20 fire season and a record number of sustained outbreaks of pyroCbs occurred.\  However, the five fires examined here were not all associated with pyroCb, highlighting that it is not the sole weather phenomenon associated with extreme fire behaviour. In particular, no lightning was detected within the Green Valley Talmalmo fire (that subsequently became the Corryong fire when it burned into Victoria) as it burned through Green Valley, which shows that dangerous tornado-strength fire-generated winds can occur without pyroCb.

The simulations produced fire-generated extreme winds associated with both rotation and straight-line flow, which present a serious hazard. ACCESS-Fire simulated rotating winds in the updraft of the Green Valley Talmalmo/Corryong fire. More work is required to understand the mechanisms for these, they are likely related to the high intensity of the fire, coupled with topographic influences.

Spot fires were an important component in the observed rate of spread, particularly in the forest fires overnight. The extremely dry, drought-affected fuel beds meant that the ignition efficiency of spot fires was enhanced compared to an average season. Inclusion of a spotting parameterisation in ACCESS-Fire would accelerate the forwards fire spread and improve validation of the simulated fire perimeters.\ 

Coastal processes were evident in the simulations of the Kangaroo Island and Yanchep fires. Localised wind effects in the simulations showed interactions between the fire and maritime airmass including sea breeze circulations can modify the updrafts associated with the fire as well as produce rapid transitions in fire intensity around a fire perimeter. Cooler moister air associated with a maritime airmass may not necessarily reduce fire intensity, depending on its depth and penetration inland.

Utilisation - where to from here?

The high level of engagement in this work from a range of stakeholders has demonstrated the value of this research and the appetite for operational application.\ 

The learnings from this work should be incorporated into training packages tailored for fire meteorologists and FBANs that describe characteristics of the local meteorological environment favourable for extreme fire behaviour. Such training will complement other current research and training on fire behaviour aspects such as spotting and potential for pyroCb.

This work, which has been conducted in close collaboration with partners in fire agencies, has demonstrated that a comprehensive understanding of the mechanisms driving fire behaviour requires a multidisciplinary approach. Similarly, the successful application of fire behaviour and meteorology knowledge in operations requires locally connected specialised expertise, combined with tailored modelling tools to inform objective, evidence-based decisions.

The insights gathered from these five case studies have further demonstrated the value of this high resolution coupled modelling approach. In order to progress ACCESS-Fire to an effective operational tool, more robust testing of the model is required, in addition to the more subjective assessments that have been made through the case study work. This would include technical testing, additional sensitivity testing and routine verification.

This project has demonstrated that the Bureau{\textquoteright}s technology and simulation capability, scientific expertise and established relationships with fire agencies can meet the Australian community{\textquoteright}s need to understand the drivers of fire behaviour during the 2019-20 fire season. In doing so, we have further developed and validated our modelling systems and made progress towards their future operational use.

}, keywords = {ACCESS-Fire, black summer, coupled, fire-atmosphere, simulations}, issn = {705}, author = {Mika Peace and Barry Hanstrum and Jesse Greenslade and Dragana Zovko-Rajak and Abhik Santra and Jeffrey Kepert and Paul Fox-Hughes and Harvey Ye and Tasfia Shermin and Jeffrey Jones} } @article {bnh-7509, title = {Coupled fire-atmosphere modelling: ACCESS-Fire {\textendash} annual report 2019-2020}, number = {630}, year = {2020}, month = {11/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {MELBOURNE}, abstract = {

This project aims to improve understanding of fire and atmosphere interactions and feedback processes through running the coupled fire-atmosphere model ACCESS-Fire.

Project deliverables include: preparation of meteorological and simulation case studies of significant fire events; installation and testing of the ACCESS-Fire coupled model on the National Computing Infrastructure (NCI) and preparation of training material to support operational implementation of research findings.

The project started in March 2016, and progress over the past four years has been on several aspects:

  1. ACCESS-Fire has been installed on NCI and substantial investment has been made in testing and developing the model
  2. A meteorological case study of the Waroona fire has been published, which generated outreach activities across numerous agencies and jurisdictions.
  3. ACCESS-Fire has been run on two fires: the Waroona fire in WA and the Sir Ivan fire in NSW. A draft of the results of the Waroona simulations has been prepared and analysis and manuscript outline of the Sir Ivan simulations is well underway.
  4. Operational support was requested by fire agencies and the Bureau during high-impact events during the 2019-20 fire season. Support was provided in CFS and SES in SA, RFS in NSW and QFES in QLD during the protracted fire campaigns.
  5. A draft of the paper {\textquoteleft}Lessons learned from coupled fire-atmosphere research and implications for operational fire modelling{\textquoteright} has been prepared.

The project has continued to participate strongly in outreach activities, including media engagement through extended radio interviews and collaboration on print and online news articles.\  Conference presentations, high level training presentations and panel participation on topics including fire science, High Performance Computing, STEM careers and Women in Leadership have been attended.

The project has demonstrably achieved the objective of building and sharing national capability in fire research and has repeatedly applied that knowledge in critical focus during high impact events in support of end-users inside their operational centers.\  That outcome is not a specific project deliverable and is to some degree intangible, so not as easily measured as outcomes such as publications. \ However, it demonstrates successful realization of the CRC objective of building collaborations and trusted partnerships and strengthening national capability. The capability is recognized and valued across fire and land management agencies and in the Bureau; value that is evidenced by the repeated requests to provide high-level fire and meteorological interpretation inside operations.\ 

We therefore thank BNHCRC for their understanding in allowing flexible deadlines and repeatedly negotiating project timelines and deliverables, as this flexibility to shifting priorities has enabled the project team to provide operational support when it was needed.

Our focus for the remainder of the project is to complete advanced drafts of the papers to ensure that our key findings are documented in the scientific literature and expand the body of knowledge from coupled modelling studies. \ We will also share the results with a range of audiences through three online presentations and recordings during which we intend to develop presenting experience in more junior members of the project team.

These objectives may be challenging, due to the need to work from home during the Coronavirus pandemic and the need to be flexible with plans.

We are confident that we will bring the project to completion and are gratified that along the way we have shared a valuable legacy of knowledge, analysis techniques and software that can benefit the field of meteorology and fire prediction and the Australian community into the future.

}, keywords = {ACCESS-Fire, coupled, fire-atmosphere, modelling}, issn = {630}, author = {Mika Peace and Jeffrey Kepert and Harvey Ye and Jesse Greenslade} } @article {bnh-6801, title = {Improved predictions of severe weather to reduce community impact}, number = {556}, year = {2020}, month = {03/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The project has completed the second year of its refresh and is progressing with some challenges. The first 3{\textonehalf} years featured a strong focus on developing underpinning science in some important areas, notably the transport of embers by bushfire plumes, and understanding the origin of the moisture when pyrocumulus clouds form {\textendash} is it from the atmosphere, or from the fuel? We also conducted significant case studies, including an ensemble-based study of a severe east coast low, an analysis of the meteorology of the State Mine Fire of October 2013, and a study into tropical cyclone secondary eyewall formation.

This second phase of the project pivots towards utilization. We will not neglect investigations into the underpinning science, or case studies, but we are looking to turn our previous discoveries and knowledge gained into useful products.

The first of these is a new thermodynamic tool for predicting the potential for pyrocumulonimbus (pyroCb) formation, the Pyrocumulonimbus Firepower Threshold, or PFT. This parameter depends on the atmospheric state, both the wind strength within the boundary layer and the full thermodynamic profile and aims to predict the minimum fire power (in GW) that is necessary to trigger deep convection. In favourable conditions, a fire of a few GW suffices, and at unfavourable times, 1000 GW would be insufficient. We have found that there is substantial variability in the atmospheric favourability in time and space, and that observed pyroCb often form during a narrow window of opportunity. We are presently preparing for a major utilization exercise, a near-real time trial of the tool over the coming summer. We expect that the results from this trial will help to finalize the development of the tool, and ready it for operations.

Our case study of the tornado outbreak in South Australia that triggered events which cut power to the entire state showed that the tornado cluster was predictable by modern high-resolution numerical weather prediction (NWP) {\textendash} indeed, the deterministic model predicted the precise location of one of the observed tornadoes. Encouraged by this success, we ran a 6-member ensemble simulation of the event, which showed that while the probability of tornadoes was well over 50\%, the level and location of the activity was less certain. To assist with analysis of this event, we also developed a novel diagnostic of tornadic precursors in NWP systems. A journal article is almost ready for submission on this work.

A second case study is analyzing the Tathra bushfire on the south coast of New South Wales, which led to the destruction of over 60 houses. Although occurring in strong northwesterly winds in the lee of the ranges, mountain wave activity appears to have been modest at the time of the greatest fire activity and probably not the major cause of the disaster. Rather, the extreme fire behavior appears to have been driven by strong, very unsteady and fluctuating winds, caused by roll-like circulations in the flow off the ranges, with the interaction between this flow and a later wind change also of interest. The weak role of mountain waves in this event illustrates the value of performing detailed case studies, as at first glance, several of the ingredients for a mountain wave event were present, and indeed active earlier in the day.

Unfortunately, our development of a parameterization of long-range ember transport has made little progress this year, due to the unanticipated difficulty of the task and the illness of a staff member. We plan to resume work on that shortly.

In recognition of the delays on the ember transport parameterization, and also of new opportunities that have arisen in pyrocumulus prediction, we have negotiated an altered project schedule with the BNHCRC.

}, keywords = {community impact, predictions, Severe Weather}, issn = {556}, author = {Jeffrey Kepert and KJ Tory and Dragana Zovko-Rajak and David Wilke and Serena Schroeter} } @article {bnh-7773, title = {Pyrocumulonimbus Firepower Threshold: Assessing the atmospheric potential for pyroCb}, journal = {Weather and Forecasting}, year = {2020}, month = {12/2020}, abstract = {

Pyrocumulonimbus (pyroCb) clouds are difficult to predict and can produce extreme and unexpected wildfire behaviour that can be very hazardous to fire crews. Many forecasters modify conventional thunderstorm diagnostics to predict pyroCb potential, by adding temperature (Δθ) and moisture increments (Δq) to represent smoke plume thermodynamics near the expected plume condensation level. However, estimating these Δθ\ and Δq\ increments is a highly subjective process that requires expert knowledge of all factors that might influence future fire size and intensity. In this paper, instead of trying to anticipate these Δθ\ and Δq\ increments for a particular fire, the minimum firepower required to generate pyroCb for a given atmospheric environment is considered. This concept, termed the PyroCb Firepower Threshold (PFT) requires only atmospheric information, removing the need for subjective estimates of the fire contribution.

A simple approach to calculating PFT is presented that incorporates only basic plume-rise physics, yielding an analytic solution that offers important insight into plume behaviour and pyroCb formation. Minimum increments of Δθ\ and Δq\ required for deep, moist convection, plus a minimum cloud-base height (Zfc), are diagnosed on a thermodynamic diagram. Briggs plume rise equations are used to convert Δθ,\ Zfc, and a mean horizontal windspeed (U) to a measure of the PFT: the minimum heat flux entering the base of the plume. This PFT is proportional to the product of\ U, Δθ, and the square of\ Zfc. Plume behaviour insights provided by the Briggs equations are discussed, and a selection of PFT examples presented.

}, keywords = {atmosphere, fire power, Fire weather, meteorology, pyrocumulonimbus}, doi = {https://doi.org/10.1175/WAF-D-20-0027.1}, url = {https://journals.ametsoc.org/view/journals/wefo/aop/WAF-D-20-0027.1/WAF-D-20-0027.1.xml}, author = {KJ Tory and Jeffrey Kepert} } @conference {bnh-6410, title = {ACCESS-Fire: coupled fire-atmosphere modelling}, booktitle = {Bushfire and Natural Hazards CRC Research Day AFAC19}, year = {2019}, month = {12/2019}, address = {Melbourne}, abstract = {

Coupled models are a class of fire prediction models that integrate a fire component with an atmospheric component, to examine how the energy released by a fire modifies the surrounding atmosphere. Coupled models can resolve complex interactions between the fire, topography and atmosphere, which subsequently manifest on fire behaviour. Results from simulations promote understanding of the driving processes in dynamic fire events. This can inform development of predictive tools that may be used to anticipate extreme fire behaviour and mitigate against the impacts of significant fires.

Globally, several coupled models have been developed; mostly by meteorological institutions for application in a research capacity. They can be broadly separated as taking either physical or empirical modelling approaches. We are running ACCESS-Fire; an empirical coupled model. It links the research version of the Australian Community Climate and Earth System Simulator (ACCESS) Numerical Weather Prediction (NWP) to a set of empirically derived fire spread equations. In this presentation we will describe the coupled fire-atmosphere model ACCESS Fire and report on progress on simulations of recent significant fire events.

In Australia and overseas, the imperative for accurate, flexible and timely predictions for prescribed (fuel reduction) burns and bushfires will only increase. Incorporating complex, dynamical meteorological fields is a critical component in building fire prediction systems that can resolve some of the most destructive elements of fire behaviour. Although coupled fire-atmosphere models are currently limited in producing timely operational output due to computational requirements, these restrictions will diminish as technology capabilities continue to increase.

}, keywords = {coupled models, Fire behaviour, fire-atmosphere, Forecasting, modelling}, url = {https://knowledge.aidr.org.au/resources/australian-journal-of-emergency-management-monograph-series/}, author = {Mika Peace and Jeffrey Kepert and Harvey Ye} } @conference {bnh-6511, title = {A case study of South Australia{\textquoteright}s severe thunderstorm and tornado outbreak }, booktitle = {AFAC19 powered by INTERSCHUTZ - Bushfire and Natural Hazards CRC Research Forum}, year = {2019}, month = {12/2019}, publisher = {Australian Institute for Disaster Resilience}, organization = {Australian Institute for Disaster Resilience}, address = {Melbourne}, abstract = {

On September 28, 2016 one of the most significant thunderstorm outbreaks recorded in South Australia impacted central and eastern parts of the state. Multiple supercell thunderstorms were embedded in a Quasi-Linear Convective System aligned with a strong cold front that was associated with an intense low-pressure system. The storms produced at least seven tornadoes, destructive wind gusts, large hail and intense rainfall. Transmission lines were brought down in four different locations, which contributed to a state-wide power outage.

Accurate prediction and understanding of tornadoes and other hazards associated with severe thunderstorms is very important, for timely preparation and announcement of warnings. By conducting high-resolution simulations, this study aims to offer a better understanding of the meteorology of the South Australian thunderstorm and tornado outbreak. It also contributes to improving knowledge of how to best predict similar severe weather events, which in turn enables better risk management and preparedness for such events. Updraft
helicity, a severe storm surrogate that indicates the potential for updraft rotation in simulated storms, is used to investigate the ability of the model to predict supercell and tornado likelihood.

Download the full non-peer reviewed research proceedings\ from the Bushfire and Natural Hazards CRC Research Forumhere.

}, keywords = {modelling, risk management, Severe Weather, thunderstorm, tornado}, url = {https://knowledge.aidr.org.au/resources/australian-journal-of-emergency-management-monograph-series/}, author = {Dragana Zovko-Rajak and KJ Tory and Jeffrey Kepert} } @article {bnh-5775, title = {Coupled fire atmosphere modelling annual report 2018-2019}, number = {501}, year = {2019}, month = {08/2019}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The project goal is to improve understanding of fire and atmosphere interactions and feedback processes through running a coupled fire-atmosphere simulation model. Planned project outcomes include: preparation of meteorological and simulation case studies of significant fire events, installation and testing of the ACCESS-Fire coupled model on the National Computing Infrastructure (NCI) and preparation of training material to support operational implementation of research findings.

The project started in March 2016, and progress over the past three years has been on several fronts; 1) publication of a case study of the Waroona fire and related outreach activities 2) implementing, developing and testing the coupled fire-atmosphere model ACCESS-Fire 3) operational support during high-impact events and 4) draft of the paper {\textquoteright} Lessons learned from coupled fire-atmosphere research and implications for operational fire modelling{\textquoteright}.

}, keywords = {bushfire prediction, coupled-fire, fire behavour. fire impacts, modelling}, issn = {501}, author = {Mika Peace and Jeffrey Kepert and Harvey Ye} } @article {bnh-5432, title = {Impact-Based Forecasting for the Coastal Zone: East Coast Lows- Annual Report 2017/2018}, number = {463}, year = {2019}, month = {03/2019}, pages = {1-28}, type = {Report}, keywords = {Built Environment, Forecasting, Severe Weather}, issn = {463}, author = {Harald Richter and Craig Arthur and Serena Schroeter and Martin Wehner and Jane Sexton and Beth Ebert and Mark Dunford and Jeffrey Kepert and Shoni Maguire and Russell Hay and Mark Edwards} } @article {bnh-5145, title = {The boundary layer dynamics of tropical cyclone rainbands}, journal = {Journal of the Atmospheric Sciences}, volume = {75}, year = {2018}, month = {09/2018}, abstract = {

Spiral bands are ubiquitous features in tropical cyclones and significantly affect boundary layer thermodynamics, yet knowledge of their boundary layer dynamics is lacking. Prompted by recent work that has shown that relatively weak axisymmetric vorticity perturbations outside of the radius of maximum winds in tropical cyclones can produce remarkably strong frictional convergence, and by the observation that most secondary eyewalls appear to form by the {\textquotedblleft}wrapping up{\textquotedblright} of a spiral rainband, the effect of asymmetric vorticity features that mimic spiral bands is studied. The mass field corresponding to an axisymmetric vortex with added spiral vorticity band is constructed using the nonlinear balance equation, and supplied to a three-dimensional boundary layer model. The resulting flow has strong low-level convergence and a marked updraft extending along the vorticity band and some distance downwind. There is a marked along-band wind maximum in the upper boundary layer, similar to observations, which is up to about 20\% stronger than the balanced flow. A marked gradient in the inflow-layer depth exists across the band and there is an increase in the surface wind factor (the ratio of surface wind speed to nonlinear-balanced wind speed) near the band. The boundary layer dynamics near a rainband therefore form a continuum with the flow near a secondary eyewall. None of these features are due to convective momentum transports, which are absent from the model. The sensitivities of the flow to band length, width, location, crossing angle, and amplitude are examined, and the possible contribution of boundary layer dynamics to the formation of the tropical cyclone rainbands discussed.

}, doi = {https://doi.org/10.1175/JAS-D-18-0133.1}, url = {https://journals.ametsoc.org/doi/abs/10.1175/JAS-D-18-0133.1}, author = {Jeffrey Kepert} } @conference {bnh-4792, title = {Impact-based forecasting for the coastal zone}, booktitle = {AFAC18}, year = {2018}, month = {09/2018}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Perth}, abstract = {

Strong surface wind gusts and heavy rain are meteorological hazards that are predominantly produced by storms such as east coast lows, tropical cyclones or thunderstorms. Interest in these hazards from a response agency point of view lies in their impact on the natural and built environment. At present, weather forecast models still predict mostly {\textquoteright}raw{\textquoteright} meteorological output such as surface wind speeds at certain times, or rain accumulations over a specified period. This model output needs to be combined with exposure and vulnerability information to translate the forecast hazard into predicted impact.

The Bushfire and Natural Hazards CRC project Impact-based forecasting for the coastal zone: East-Coast Lows attempts to demonstrate a pilot capability to deliver impact forecasts for residential housing from an ensemble of weather prediction models runs. The project is a collaborative effort between the Australian Bureau of Meteorology and Geoscience Australia.

The project is initially focusing on the wind and rainfall impact from the 20-22 April 2015 east coast low event in NSW. The wind and rainfall hazard data are provided by a 24-member ensemble of the ACCESS model on a 1.3 km grid, with damage data acquired from NSW State Emergency Services (SES) and the Emergency Information Coordination Unit (EICU) for the 2015 event.

We will show that the multi-hazard nature of an east coast low event makes attributing the observed building damage to a single hazard difficult. Wind damage to residential housing in this case is largely due to tree fall. This {\textquoteright}damage-byintermediary{\textquoteright} mechanism requires not just the knowledge of building properties in an exposed area, but also additional knowledge of the surrounding vegetation and its response to strong winds. We will discuss enhancements to the SES/EICU damage survey templates that would lead to improvements in the development of the hazard-damage relationships.

}, author = {Harald Richter and Craig Arthur and Serena Schroeter and Martin Wehner and Jane Sexton and Beth Ebert and Mark Dunford and Jeffrey Kepert and Shoni Maguire and Russell Hay and Mark Edwards} } @conference {bnh-4766, title = {Simulations of the waroona fire with the access-fire coupled fire atmosphere model}, booktitle = {AFAC18}, year = {2018}, month = {09/2018}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Perth}, abstract = {

The Australian Community Climate and Earth-System Simulator (ACCESS) Numerical Weather Prediction (NWP) model has been coupled to a fire spread prediction model called ACCESS-Fire (Monash and Melbourne universities, publication in preparation). The ACCESS-Fire model presents a coupled fire-atmosphere modelling capability that is linked to the Australian Bureau of Meteorology{\textquoteright}s operational weather forecasting system.\ 


The fire spread code in ACCESS-Fire is implemented by a level set solver and includes several fire spread models, including options for Rothermel, McArthur and CSIRO forest and grassland. It uses high-resolution topography and detailed fuel maps can be included as available. The sensible and latent heat energy fluxes from the fire are passed back to the atmospheric code through the land-surface scheme JULES. The fire model has been built into the ACCESS high-resolution nested suite using an advanced graphical user and scheduler interface.

ACCESS-Fire simulations have been run on the Waroona fire, which burnt over 68,000 ha south of Perth in January 2016. Over 160 homes were destroyed and there were two fatalities. During the first two days of the fire, there were four episodes of extreme fire behaviour. Two separate pyrocumulonimbus events developed and two evening ember storms occurred. The fire behaviour at the Waroona fire was driven by three dimensional fire-atmosphere interactions, and such processes can be examined using a coupled fire-atmosphere model.

This paper will describe key features of the coupled fire-atmosphere model ACCESSFire and present results from simulations of the Waroona fire. Features of the simulations include fire-modified winds in the environmental flow, dynamic plume effects near steep topography and exploration of pyrocumulonimbus processes.

}, author = {Mika Peace and Jeffrey Kepert and Harvey Ye} } @article {bnh-5184, title = {Wave ensemble forecasts for tropical cyclones in the Australian region}, journal = {Ocean Dynamics}, volume = {68}, year = {2018}, month = {05/2018}, pages = {603-625}, chapter = {603}, abstract = {

Forecasting of waves under extreme conditions such as tropical cyclones is vitally important for many offshore industries, but there remain many challenges. For Northwest Western Australia (NW WA), wave forecasts issued by the Australian Bureau of Meteorology have previously been limited to products from deterministic operational wave models forced by deterministic atmospheric models. The wave models are run over global (resolution 1/4o) and regional (resolution 1/10o) domains with forecast ranges of + 7 and + 3 day respectively. Because of this relatively coarse resolution (both in the wave models and in the forcing fields), the accuracy of these products is limited under tropical cyclone conditions. Given this limited accuracy, a new ensemble-based wave forecasting system for the NW WA region has been developed. To achieve this, a new dedicated 8-km resolution grid was nested in the global wave model. Over this grid, the wave model is forced with winds from a bias-corrected European Centre for Medium Range Weather Forecast atmospheric ensemble that comprises 51 ensemble members to take into account the uncertainties in location, intensity and structure of a tropical cyclone system. A unique technique is used to select restart files for each wave ensemble member. The system is designed to operate in real time during the cyclone season providing + 10-day forecasts. This paper will describe the wave forecast components of this system and present the verification metrics and skill for specific events.

}, doi = {https://doi.org/10.1007/s10236-018-1145-9}, url = {https://link.springer.com/article/10.1007\%2Fs10236-018-1145-9}, author = {Stefan Zieger and Diana Greenslade and Jeffrey Kepert} } @article {bnh-3924, title = {The contribution of turbulent plume dynamics to long-range spotting}, journal = {International Journal of Wildland Fire}, volume = {26}, year = {2017}, month = {03/2017}, pages = {317-330}, chapter = {317}, abstract = {

Spotting can start fires up to tens of kilometres ahead of the primary fire front, causing rapid spread and placing immense pressure on suppression resources. Here, we investigate the dynamics of the buoyant plume generated by the fire and its ability to transport firebrands. We couple large-eddy simulations of bushfire plumes with a firebrand transport model to assess the effects of turbulent plume dynamics on firebrand trajectories. We show that plume dynamics have a marked effect on the maximum spotting distance and determine the amount of lateral and longitudinal spread in firebrand landing position. In-plume turbulence causes much of this spread and can increase the maximum spotting distance by a factor of more than 2 over that in a plume without turbulence in our experiments. The substantial impact of plume dynamics on the spotting process implies that fire spread models should include parametrisations of turbulent plume dynamics to improve their accuracy and physical realism.

}, doi = {10.1071/WF16142}, url = {http://www.publish.csiro.au/wf/WF16142}, author = {W. Thurston and Jeffrey Kepert and KJ Tory and Robert Fawcett} } @article {bnh-4204, title = {Coupled fire-atmosphere modelling project: annual project report 2016-17}, number = {307}, year = {2017}, month = {09/2017}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The goal of the project is to improve understanding of fire and atmosphere interactions and feedback processes by running a coupled fire-atmosphere simulation model.\  Planned outcomes of the project include: preparation of meteorological and simulation case studies of significant fire events, installation and testing of a coupled model on the national computing infrastructure and preparation of training material to support operational implementation of research findings.

Weather forecasting and fire prediction are similar in that skilled practitioners of both rely on a combination of detailed scientific knowledge and objective analysis, juxtaposed with pattern recognition that draws on past experience and a mental inventory of previous events.\ \  By preparing detailed case studies and coupled simulations of events where unexpected or unusual fire-atmosphere interactions occurred, we contribute to both the scientific understanding for fire{\textendash}atmosphere interactions and the knowledge base of operational meteorologists and fire analysts.

The project started in March 2016, and work for the first year and a quarter has been on two main fronts; a case study of the Waroona fire and implementing the coupled fire-atmosphere model ACCESS-Fire.

The Waroona fire in Western Australia in January 2016 was selected as the first case study. It was a complex event, with \ significant impacts including the destruction of the town of Yarloop. A detailed paper on the Waroona fire has been prepared and the manuscript submitted to the Journal of Southern Hemisphere Earth Systems and Science (JSHESS). The paper is expected to be published by late 2017. The paper is the result of a collaborative effort between Department of Parks and Wildlife, WA and research and operational representatives from the Bureau of Meteorology. The work has been presented at a number of forums and has been accepted for oral presentation at two major conferences in late 2017.

Progress with the coupled model ACCESS-Fire (ACCESS is the Australian Community Climate and Earth-System Simulator) has been slower than anticipated, but significant headway has been made. ACCESS high resolution nested suites are now running on the project space on the National Computing Infrastructure. Importantly, the framework is more generic than the original code and can be easily re-configured to relocate and run for a new event anywhere in Australia. The nested suites are now running successfully in the advanced graphical user interface "Rose-Cylc" which will receive ongoing support and development from the UK Met Office. The fire code has been implemented on the JULES land-surface scheme and final testing is in progress.

}, issn = {307}, author = {Jeffrey Kepert and Mika Peace and Harvey Ye} } @article {bnh-4232, title = {Improved predictions of severe weather to reduce community impact: midterm report 2014-17}, number = {315}, year = {2017}, month = {09/2017}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

This report marks the end of the initially-approved 3{\textonehalf} years of the project. To\ mark that milestone, this annual report is much longer than previous annual\ reports, for it is also the final report of that initial part of the project, and as such\ contains detailed descriptions of the six main activities in the first 3{\textonehalf} years.

We have studied the dynamics, predictability and processes of severe weather, including fire weather, with the purpose of improving forecasts of severe weather and better depicting forecast uncertainty in these events, thereby facilitating better risk management and more cost-effective mitigation.

Two of the six main chapters of this report relate to our work with large-eddy modelling of turbulent plumes. We have used this technology, in which the model is run on a 50-m grid to capture the most energetic size range of the turbulent eddies, to both simulate ember transport and to model pyrocumulus formation. The mean travel distance of firebrands depends mainly on wind speed and fire intensity, but the spread in the landing positions shifts from being substantially cross-wind at light winds, to dominantly along-wind at high winds. This spread is greatly increased by the turbulence in the plume, and the maximum spotting distance can be more than double the mean for this reason.\ 

We have also used our plume modelling to study pyrocumulus clouds. We have analyzed the processes that lead to pyrocumulus, with special attention on the relative importance of moisture from two sources, the atmosphere and combustion, and shown that the latter is negligible except in very dry environments. This somewhat controversial result has been confirmed by a conceptual study of the thermodynamics of pyrocumulus formation.

We have prepared three detailed studies of severe weather events. East coast lows are intense low-pressure systems that form over the sea adjacent to the east coast of Australia, most commonly along the New South Wales coast. We analyzed the 20-23 April 2015 event using, for the first time, an ensemble of 24 simulations rather than just a single forecast. The use of an ensemble allows us to better discern the degree of risk, and to account for the inherent uncertainty in any forecast. It also enables insight into the processes that lead to the rapid intensification of these systems.\ 

The Blue Mountains fires of October 2013 were most damaging on the 17th. This was expected to be a day of high fire risk, but the extreme fire spread was not anticipated and the causes were unknown. Our high resolution simulations showed that the downward extension of high upper-level winds to the vicinity of the fire ground, caused by mountain wave activity, was a factor. A dry slot {\textendash} that is, a long, relatively narrow band of dry air {\textendash} which moved over the fire, further contributed to the conditions.

Lastly, we have analyzed a simulation of a secondary eyewall formation and eyewall replacement cycle in a tropical cyclone, yielding better understanding of the underlying processes and the important factors in predicting these developments. Eyewall replacement cycles are associated with marked expansions of the tropical cyclone wind field, leading to a wider damage swath, earlier onset of damaging winds, and increased storm surge and wave damage.\ 

We are pleased that the project will continue for another three years. Our focus will shift to a greater emphasis on utilization activities during this period. In particular, we aim to develop simple methods of calculating ember transport and pyrocumulus development, so as to transfer the knowledge we have developed in these areas into operations. We will also continue to study severe weather events in detail.

}, issn = {315}, author = {Jeffrey Kepert and KJ Tory and W. Thurston and Dragana Zovko-Rajak and Ching, Eng and Robert Fawcett} } @conference {bnh-3904, title = {Lessons learned from a multidisciplinary investigation into the Waroona fire}, booktitle = {AFAC17}, year = {2017}, month = {09/2017}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Sydney}, abstract = {

The Waroona fire burnt over 68,000 ha and destroyed more than 160 homes in southwest Western Australia in January 2016.\ \  This conference paper is an abbreviated and less technical version of a longer case study that has been submitted to the Journal of Southern Hemisphere Earth Systems Science (Peace et al., 2017). More detail and supporting analysis is contained in the JSHESS version and interested readers are directed there.

Our investigation revealed processes that contributed to four episodes of extreme fire behaviour and the findings are highly relevant to other fires where extreme fire behaviour may develop. This study draws on two reports that highlight the difference between observed FDI{\textquoteright}s and fire activity at Waroona (Bureau of Meteorology, 2016 and McCaw et al., 2016).

There were two pyroCb events; both were associated with anomalously fast fire spread in the prevailing winds; one ignited new fires downwind and the other was against normal diurnal timing. Two evening ember storms occurred; the first impacted the town of Waroona and on the second evening, there were two fatalities when the fire made an unexpected run and produced a destructive ember storm over the town of Yarloop.

}, author = {Mika Peace and Jeffrey Kepert and Lachlan W. McCaw and Burrows, N.D. and Bradley Santos and Robert Fawcett} } @article {bnh-5070, title = {Meteorological drivers of extreme fire behaviour during the Waroona bushfire, Western Australia, January 2016}, journal = {Journal of Southern Hemisphere Earth Systems Science}, volume = {67}, year = {2017}, month = {11/2017}, pages = {79-106}, chapter = {79}, abstract = {

The Waroona bushfire burnt 69,000 ha south of Perth in January 2016. During the first two days of the fire, there were two pyrocumulonimbus (pyroCb) events and two destructive evening fire runs. Over 160 homes were destroyed and there were two fatalities. This case study examines in detail the links between the meteorological observations and the fire behaviour reconstruction.

The first pyroCb developed on Wednesday 6 January 2016, when the fire made an unexpectedly fast run in light prevailing winds. The pyroCb produced lightning strikes that ignited a new fire downwind of the main head fire. A second pyroCb developed on Thursday morning, against normal diurnal thunderstorm trends. Similar to the previous evening, the fire spread faster than expected, given the near-surface meteorological conditions.

On both evenings there were destructive ember storms over the towns of Waroona (Wednesday) and Yarloop (Thursday). Examination of the meteorological observations has linked these ember showers to the onset of downslope winds, locally known as {\textquoteright}scarp winds{\textquoteright}. As downslope winds are associated with strong localised turbulence, they provide a mechanism for transport of large numbers of firebrands.

The periods of extreme fire behaviour at Waroona were against normal diurnal expectations and did not coincide with the highest observed Fire Danger Index (FDI) values, which occurred at around 1600 LT. This study links both pyroCb events to accelerated fire spread, which presents a hazard to firefighters that is not accounted for in traditional, surface based methods of fire prediction. Downslope winds similar to those that impacted the Waroona fire occur at many locations. They provide a highly localised mechanism for destructive evening ember showers.

This investigation into the Waroona fire describes the potential impacts of fireatmosphere feedback processes. Consequently, it highlights the need for predictive methods and tools that anticipate fire behaviour which is not steady-state. Planned simulations using a coupled fire-atmosphere model will allow further insights into features of this case study.

}, doi = {10.22499/3.6702.002}, url = {http://www.bom.gov.au/jshess/docs/2017/Peace.pdf}, author = {Mika Peace and Lachlan W. McCaw and Bradley Santos and Jeffrey Kepert and Burrows, N.D. and Robert Fawcett} } @conference {bnh-3877, title = {Secondary eyewall formation in tropical cyclones}, booktitle = {AFAC17}, year = {2017}, month = {09/2017}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Sydney}, abstract = {

Roughly half of all intense tropical cyclones experience an eyewall replacement cycle. In these events, a new eyewall forms concentrically around the original one. This secondary eyewall develops its own wind maximum, and both the secondary eye and the wind maximum typically intensify and contract, whilst the original eyewall and wind maximum weaken and eventually dissipate. While the evolution of a storm with concentric eyewalls is reasonably well understood, the mechanism or mechanisms by which the outer eyewall forms remain elusive. Understanding secondary eyewall formation is an important problem, for the subsequent eyewall replacement cycle can significantly affect the intensity of the storm, and the formation process and replacement cycle are usually associated with a major expansion of the outer wind field. Both these factors significantly affect the cyclone{\textquoteright}s impact.

We investigate a high resolution simulation of an eyewall replacement cycle. Boundary layer convergence due to friction substantially influences the evolution of the convection, and we present evidence for a positive feedback involving convection, vorticity and frictional convergence that governs the subsequent evolution of the system. In this feedback, frictional convergence strengthens the convection, stretching of vortex tubes in the buoyant updrafts increases the vorticity, and the vorticity structure of the storm determines the strength and location of the frictional updraft.\ 

Changes in the structure and intensity of tropical cyclones cause difficulties for their \ management, especially if these changes occur in the last day or two before landfall. Our improved knowledge of these processes will lead to better forecasts and mitigation.

}, author = {Jeffrey Kepert} } @conference {bnh-3883, title = {Thermodynamic considerations of pyrocumulus formation}, booktitle = {AFAC17}, year = {2017}, month = {09/2017}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Sydney}, abstract = {

In favourable atmospheric conditions, large hot fires can produce pyrocumulonimbus (pyroCb) cloud in the form of deep convective columns resembling conventional thunderstorms, which may be accompanied by strong inflow, dangerous downbursts and lightning strikes.\  These in turn may enhance fire spread rates and fire intensity, cause sudden changes in fire spread direction, and the lightning may ignite additional fires.\  Dangerous pyroCb conditions are not well understood and are very difficult to forecast.\ 

Here, a conceptual study of the thermodynamics of fire plumes is presented to better understand the influence of a range of factors on plume condensation.\  Recognising that plume gases are undilute at the fire source and approach 100\% dilution at the plume top (neutral buoyancy), we consider how the plume condensation height changes for this full range of dilution and for a given set of factors that include: environmental temperature and humidity, fire temperature, and fire moisture to heat ratios.\  The condensation heights are calculated and plotted as saturation point (SP) curves on thermodynamic diagrams for a broad range of each factor.\  The distribution of SP curves on thermodynamic diagrams provides useful insight into pyroCb behaviour. Adding plume temperature traces from Large-Eddy Model simulations to the thermodynamic diagrams provides additional insight into plume buoyancy, how it varies with height, and the potential for dangerous pyroCb development.

}, author = {KJ Tory and W. Thurston and Jeffrey Kepert} } @article {bnh-3820, title = {Time and space scales in the tropical cyclone boundary layer, and the location of the eyewall updraft}, journal = {Journal of the Atmospheric Sciences}, year = {2017}, month = {07/2017}, abstract = {

The transient response of the tropical cyclone boundary layer is studied using linearized and nonlinear models, with particular focus on the frictionally-forced vertical motion. The impulsively started, linearized tropical cyclone boundary layer is shown to adjust to its equilibrium solution via a series of decaying oscillations with the inertial period 2π/I. In the nonlinear case, the oscillation period is slightly lengthened by inwards advection of the slower-evolving flow from larger radii, but the oscillations decay more quickly. In an idealized cyclone with small sinusoidal oscillations superimposed on the gradient wind, the equilibrium nonlinear boundary layer acts as a low-pass filter with pass length scaling as {\textendash}u10/I, where {\textendash}u10\ is the 10-m frictional inflow. This filter is absent from the linearized boundary layer. The eyewall frictional updraft is similarly displaced inwards of the radius of maximum winds by a distance that scales with {\textendash}u10/I, due to nonlinear overshoot of the inflowing air as it crosses the relatively sharp increase in\ I\ near the eyewall. This displacement is smaller (other things being equal) when the RMW is small, and greater when it is large, including in secondary eyewalls. The dependence of this distance on {\textendash}u10/I\ may explain, at least partially, why observed RMWs are seldom less than 20 km, why storms with relatively peaked radial profiles of wind speed can intensify more rapidly, and why some secondary eyewalls initially contract rapidly with little intensification, then contract more slowly while intensifying.

}, doi = {10.1175/JAS-D-17-0077.1}, url = {http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-17-0077.1}, author = {Jeffrey Kepert} } @article {bnh-2920, title = {Coupled fire-atmosphere modelling: Annual project report 2015-2016}, number = {179}, year = {2016}, month = {08/2016}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The goal of the project is to improve understanding of fire and atmosphere interactions and feedback processes by running a coupled fire-atmosphere simulation model. Planned outcomes of the project include: preparation of meteorological and simulation case studies of significant fire events, installation and testing of a coupled model on the national computing infrastructure and preparation of training material to support operational implementation of research findings.\ Weather forecasting and fire prediction are similar in that skilled practitioners of both rely on a combination of detailed scientific knowledge and objective analysis, juxtaposed with pattern recognition that draws on past experience and a mental inventory of previous events. By preparing detailed case studies and coupled simulations of events in which unexpected or unusual fire-atmosphere interactions occurred, we contribute to both the scientific understanding for fire{\textendash}atmosphere interactions and the knowledge base of operational meteorologists and fire analysts.

The project has been staffed for just four months, and is commencing work on two main fronts. The first of these is implementing the coupled model ACCESS-Fire (ACCESS is the Australian Community Climate and Earth-System Simulator). We have obtained the source code from Monash University and are preparing for installation and testing. Progress has been slowed a little by a major change in the ACCESS model infrastructure, which has mean that some necessary components for very high resolution simulation are not yet available. We attended an ACCESS training workshop to ensure that we have the necessary skills to properly run the model.

After extensive consultation with end users, we have identified the Waroona fire in Western Australia (WA) in January 2016 as our first case study. This was a significant and complex event, with the impacts including the destruction of the town of Yarloop. We have made good progress on collecting and analysing data and preparing an initial draft report that describes the meteorology and fire activity during the first two days of this event, in collaboration with Western Australian fire scientists. We have also prepared an initial simulation of the event, without fire coupling

}, issn = {179}, author = {Jeffrey Kepert and Mika Peace} } @article {bnh-2675, title = {Coupled fire-atmosphere simulations of the Rocky River fire using WRF-SFIRE}, journal = {Journal of Applied Meteorology and Climatology}, volume = {55}, year = {2016}, month = {04/2016}, abstract = {

The coupled atmosphere-fire behaviour model WRF-SFIRE has been used to simulate a fire where extreme fire behaviour was observed. Tall flames and a dense convective smoke column were features of the fire as it burnt rapidly up the Rocky River gully on Kangaroo Island, South Australia. WRF-SFIRE simulations of the event show a number of interesting dynamical processes resulting from fire-atmosphere feedback including that: fire spread was sensitive to small changes in mean wind direction; fire perimeter was affected by wind convergence resulting from interactions between the fire, atmosphere and local topography; and the fire plume mixed high momentum air from above a strong subsidence inversion. At one-minute intervals, output from the simulations showed fire spread exhibiting fast and slow pulses. These pulses occurred coincident with the passage of mesoscale convective (Rayleigh-B{\`e}nard) cells in the planetary boundary layer. Simulations show that feedback between the fire and atmosphere may have contributed to the observed extreme fire behaviour. The findings raise questions as to the appropriate information to include in meteorological forecasts for fires as well as future use of coupled and uncoupled fire simulation models in both operational and research settings.

}, url = {http://journals.ametsoc.org/doi/10.1175/JAMC-D-15-0157.1}, author = {Mika Peace and Trent Mattner and Graham A. Mills and Jeffrey Kepert and Lachlan W. McCaw} } @conference {bnh-2944, title = {The effects of turbulent plume dynamics on long-range spotting}, booktitle = {AFAC16}, year = {2016}, month = {08/2016}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Brisbane}, abstract = {

Spotting is a hazardous phenomenon which leads to unpredictable fire behaviour and accelerated fire spread. Spot fires occur when embers are launched by bushfire plumes into the background wind, which then carries the embers a significant distance from the fire front. If the embers land in a suitable fuel bed and are still burning a spot fire may be ignited. The magnitude of the problem is illustrated by Cruz et al. (2012), who provide evidence of long-range spotting in excess of 30 km during the Black Saturday bushfires of February 2009. Therefore a better understanding of the processes that contribute to long-range spotting is essential for the prediction of fire spread. In this study we aim to assess the contribution of turbulent plume dynamics to the process of long-range spotting.

}, author = {W. Thurston and KJ Tory and Robert Fawcett and Jeffrey Kepert} } @article {bnh-2974, title = {Improved predictions of severe weather to reduce community impact: Annual project report 2015-2016}, number = {169}, year = {2016}, month = {05/09/2016}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

We aim to study the dynamics, predictability and processes of severe weather, including fire weather. We seek also to improve forecasts of severe weather, and to better depict forecast uncertainty in these events, thereby facilitating better risk management and more cost-effective mitigation. Our research into ember transport in smoke plumes and the meteorology of the Blue Mountains bushfires of October 2013 has reached maturity, and journal articles have been written. We continue to develop our work on pyrocumulus clouds, and the east coast low event of April 2015, and have commenced a study of an eyewall replacement cycle in a tropical cyclone. These studies span a wide range of time and space scales and require a range of different methods.

Our ember transport work has confirmed that the mean travel distance of firebrands for a given fire intensity depends mainly on wind speed. However, the spread in the landing positions shifts from being substantially cross-wind at light winds, to dominantly along-wind at high winds. This spread is greatly increased by the turbulence in the plume, and the maximum spotting distance can be more than double the mean for this reason. These sophisticated and computationally intensive calculations can be used to inform the development of physically realistic and computationally cheap parameterizations of ember transport for use in fire models.

We have also used our plume modelling to study pyrocumulus clouds. Intense fire plumes in suitably moist environments can lead to cloud development, with the possibility of strong downbursts {\textendash} one of our simulations is shown on the cover of this report. We have analyzed the processes that lead to pyrocumulus, with special attention on the relative importance of moisture from two sources, the atmosphere and combustion, and shown that the latter is close to negligible. We aim to use the knowledge gained to develop a forecast tool for pyrocumulus formation.

Although the Blue Mountains fires of October 2013 persisted for several weeks, much of the spread occurred on the 17th. While this was expected to be a day of high fire risk, the extreme fire spread was not anticipated and the causes were unknown. Our high resolution simulations showed that the downward extension of high upper-level winds to the vicinity of the fire ground, caused by mountain wave activity, was a factor. In addition, the marked wind change on that day was associated with a dry slot, but the underlying cause of that dry slot seems to be different to previously documented cases.

East coast lows are intense low-pressure systems that form over the sea adjacent to the east coast of Australia, most commonly along the New South Wales coast. We continue our analysis of the event of 20-23 April 2015, using, for the first time, an ensemble of 24 simulations rather than just a single forecast. Collectively, these simulations accurately predict the position and intensity of the low, the strong winds and the rainfall. The differences between them give insight as to the forecast uncertainty, the overall envelope of areas at some risk, and those at highest risk. The ensemble also enables insight into the processes that lead to the rapid intensification of these systems. The risk these systems pose was further illustrated by the two events in June of 2016.

}, issn = {169}, author = {Jeffrey Kepert and KJ Tory and W. Thurston and Simon Ching and Dragana Zovko-Rajak and Robert Fawcett} } @conference {bnh-4112, title = {Large-eddy simulations of pyro-convection and its sensitivity to mositure}, booktitle = {5th International Fire Behaviour and Fuels Conference}, year = {2016}, month = {04/2016}, publisher = {International Association of Wildland Fire}, organization = {International Association of Wildland Fire}, address = {Melbourne}, abstract = {

Intense heating of air in the vicinity of a bushfire leads to deep ascent. If this ascent is deep enough to lift air above the lifting condensation level, cumulus or cumulonimbus clouds form in a process known as moist pyro-convection. There is abundant anecdotal evidence to suggest that pyro-convective clouds may have a significant impact on fire behaviour by (i) amplifying burn and spread rates (Fromm et al., 2012); (ii) enhancing spotting through plume intensification (Koo et al., 2010; Thurston et al., 2015); and (iii) igniting new fires via pyrocumulonimbus lightning, noting that pyrocumulonimbus lightning conditions favour hotter and longer-lived lightning strikes (Rudlosky and Fuelberg, 2011). Pyro-convective clouds are also responsible for the transport of smoke and other aerosols into the stratosphere, resulting in hemisphere-scale smoke transport and substantial climate impacts (Fromm et al., 2010). Therefore a knowledge of the processes that lead to the generation of moist pyro-convection is important for understanding and predicting fire behaviour, as well as the potential climatic influences of large fires. In this study we use large-eddy simulations to investigate the potential for the generation of moist pyro-convection by bushfire plumes. Firstly we perform simulations over a range of fire intensities and environmental moisture levels. Secondly we repeat a subset of these simulations with differing amounts of moisture released by the fire in order to assess the relative roles of environmental moisture and fire-derived moisture in the formation of pyro-convective clouds.

}, author = {W. Thurston and KJ Tory and Robert Fawcett and Jeffrey Kepert} } @conference {bnh-4113, title = {Long-range spotting by bushfire plumes: The effects of plume dynamics and turbulence on firebrand trajectory}, booktitle = {5th International Fire Behaviour and Fuels Conference}, year = {2016}, month = {04/2016}, publisher = {International Association of Wildland Fire}, organization = {International Association of Wildland Fire}, address = {Melbourne}, abstract = {

Spotting is a hazardous phenomenon that leads to unpredictable fire behaviour and accelerated fire spread. Spot fires occur when embers are launched by bushfire plumes into the background wind, which then carries the embers a significant distance from the fire front. If the embers land in a suitable fuel bed and are still smouldering a spot fire may be ignited. The magnitude of the problem is illustrated by Cruz et al. (2012), who provide evidence of long-range spotting in excess of 30 km during the Black Saturday bushfires of February 2009. Therefore a better understanding of the processes that contribute to long-range spotting is essential for the prediction of fire spread. In this paper we aim to assess the contribution of turbulent plume dynamics to the process of long-range spotting.

}, author = {W. Thurston and KJ Tory and Robert Fawcett and Jeffrey Kepert} } @conference {bnh-4114, title = {Mesoscale features related to the Blue Mountains fires of 17 October 2013 revealed by high resolution Numerical Weather Prediction (NWP) modelling}, booktitle = {5th International Fire Behaviour and Fuels Conference}, year = {2016}, month = {04/2016}, publisher = {International Association of Wildland Fire}, organization = {International Association of Wildland Fire}, address = {Melbourne}, author = {Simon Ching and Robert Fawcett and W. Thurston and KJ Tory and Jeffrey Kepert} } @article {bnh-2397, title = {Coupled Fire-Atmosphere Modelling}, year = {2015}, author = {Jeffrey Kepert and Mika Peace} } @conference {bnh-1614, title = {The Effects of Fire-Plume Dynamics on the Lateral and Longitudinal Spread of Long-Range Spotting Conference Paper 2014}, booktitle = {Bushfire and Natural Hazards CRC and AFAC Wellington Conference 2014}, year = {2015}, month = {02/2015}, abstract = {

The lofting of firebrands from bushfires into a background atmospheric flow can lead to spotting downwind\ of the fire front. Spotting is a hazardous phenomenon because it leads to both unpredictable\ and accelerated fire spread, as winds aloft are often in a different direction from and faster than the\ near-surface winds. Here we use a two-stage modelling process to address some of the uncertainty\ associated with spotting, by quantifying the lateral and longitudinal spread in the landing location of\ potential firebrands and how this spread is affected by the dynamics of the fire plume.

}, author = {W. Thurston and KJ Tory and Jeffrey Kepert and Robert Fawcett} } @article {bnh-2386, title = {Improved predictions of severe weather to reduce community impact: Annual project report 2014-2015}, number = {150}, year = {2015}, month = {11/2015}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

We aim to study the dynamics, predictability and processes of severe weather, including fire weather. We seek also to improve forecasts of severe weather, and to better depict forecast uncertainty in these events, thereby facilitating better risk management and more cost-effective mitigation. So far, we have studied ember transport in smoke plumes, pyrocumulus clouds, the meteorology of the Blue Mountains bushfires of October 2013, and the east coast low event of April 2015, four studies which span a wide range of time and space scales and require a range of different methods.

We are building on our existing modelling of bushfire plumes by using it to study ember transport.\  Embers are added near the base of the plumes and their trajectories calculated from the model winds. \ At higher wind speeds the embers travel further downstream than at lower wind speeds, as expected.\  However, the lateral spread is much broader for lower wind speeds. \ Understanding the spread in landing positions will facilitate the development of computationally affordable and physically realistic means of calculating the expected spotfire distribution in fire spread models.

We have further extended our plume modelling to begin a study of pyrocumulus development. Intense fire plumes in suitably moist environments can lead to cloud development, with intense updrafts and if rain develops the possibility of strong downbursts.\  Such pyro-convection may lead to enhanced and unpredictable fire spread, increased ember transport and spotting, and further ignitions from pyrocumulonimbus lightning. \ Our simulations produce realistic clouds, including the formation of rain and strong downdrafts. \ We will now examine some more cases, with the eventual aim of providing a preliminary forecast tool for pyrocumulus formation.

Although the Blue Mountains fires of October 2013 persisted for several weeks, much of the spread occurred on a single day. While this was expected to be a day of high fire risk, the extreme fire spread was unpredicted and the causes unknown. \ Our high resolution simulations helped identify the downward extension of high winds aloft in the vicinity of the fire ground, due to mountain wave activity. \ In addition, the marked wind change on that day was associated with a dry slot, known to worsen fire behaviour due to extremely low humidity.

East coast lows are intense low-pressure systems that form close to the east coast of Australia, most commonly along the New South Wales coast. They can produce severe wind, wave and flood impacts as in the event of 20-23 April 2015, which we are studying. For the first time, we are conducting this study with an ensemble of 24 simulations, rather than just a single forecast.\  Each simulation begins from a slightly different initial state, giving 24 different, but plausible, forecasts that represent a range of possible outcomes. Collectively, these simulations accurately predict the position and intensity of the low, the strong winds and the rainfall. \ The differences between them will be analysed to determine how predictable aspects of the event were.

}, issn = {150}, author = {Jeffrey Kepert and KJ Tory and W. Thurston and Simon Ching and Robert Fawcett} } @article {bnh-2404, title = {Improved predictions of severe weather to reduce community risk}, year = {2015}, author = {Jeffrey Kepert and W. Thurston and Simon Ching and KJ Tory and Robert Fawcett} } @conference {bnh-2081, title = {Large-eddy simulations of pyro-convection and its sensitivity to environmental conditions - peer viewed}, booktitle = {Adelaide Conference 2015}, year = {2015}, address = {Adelaide, Australia}, abstract = {

Research proceedings from the Bushfire and Natural Hazards CRC \& AFAC Conference in Adelaide, 1-3 September 2015.\ 

}, author = {W. Thurston and KJ Tory and Robert Fawcett and Jeffrey Kepert} } @conference {bnh-1563, title = {Managing Severe Weather - Progress and Opportunities Conference Paper 2014}, booktitle = {Bushfire and Natural Hazards CRC and AFAC Wellington Conference 2014}, year = {2015}, abstract = {

Severe weather often becomes "high impact" weather when certain {\textquotedblleft}tipping points{\textquotedblright} are reached. Rivers burst their banks, houses lose their roofs, and bushfires exceed suppression capacity as thresholds are crossed. The high adverse impact events tend to be rare, because society and the environment naturally tend to adapt to more frequent events of lower impact. They are often small scale, or a relatively small part of a larger system. And they are often subject to considerable forecast uncertainty.
Managing the impacts of severe weather is therefore about managing risk. The results of exceeding one of these thresholds are profoundly different to merely approaching it {\textendash} our memories of Hurricane Katrina would be very different if the storm surge had not been high enough to overtop and breach the levees protecting New Orleans. Often, the differences in the meteorology between a close call and a disaster will fall within current forecast uncertainty. Balancing the costs of over-preparation and under-preparation in the presence of such uncertainty is a formidable task.

}, author = {Jeffrey Kepert and Michael Naughton and John Bally} } @conference {bnh-1557, title = {Mitigating the Effects of Severe Fires, Floods and Heatwaves Conference Paper 2014}, booktitle = {Bushfire and Natural Hazards CRC and AFAC Wellington Conference 2014}, year = {2015}, abstract = {

Knowledge of landscape dryness is critical for the management and warning of fires, floods, heatwaves and landslips. This project will address fundamental limitations in our ability to prepare for these events. Currently landscape dryness is estimated using simplified soil moisture accounting systems developed in the 1960{\textquoteright}s. Similarly, flood prediction, runoff potential and water catchment/dam management also are not using the best available science and technology.
This paper describes research to be carried out by the Bushfire and Natural Hazards Cooperative Research Centre that will examine the use of detailed land surface models, satellite measurements and ground based observations for the monitoring and prediction of landscape dryness. The new information will be calibrated for use within existing fire and flood forecasting systems.
An inter-comparison will be performed of the traditional Keetch-Byram Drought Index and Soil Dryness Index with weather prediction models, satellite measurements, ground based measurements, and rainfall-runoff models. Soil moisture from weather prediction and reanalysis will be calibrated for the calculation of a high resolution historical dataset of KBDI and SDI. These datasets will be a valuable resource for researchers working on fire climatologies across Australia. The outputs of this project will improve Australia{\textquoteright}s ability to manage multiple hazard types and create a more resilient community, by developing a state of the art, world{\textquoteright}s best practice in soil moisture analysis that underpins flood, fire and heatwave forecasting.
Longer term work will explore the use of multi-model predictions and data assimilation to forecast soil dryness indices for operational application to fire, flood and heat wave hazards. The vegetation and soil parameterisations in current land surface models will be developed to match Australian conditions.

}, author = {Imtiaz Dharssi and Vinod Kumar and Yeo, Claire and John Bally and Jeffrey Kepert} } @conference {bnh-2203, title = {Modelling the Fire Weather of the Coonabarabran Fire of 13 January 2013}, booktitle = {Bushfire and Natural Hazards CRC and AFAC Wellington Conference 2014}, year = {2015}, abstract = {

We will exhibit state-of-the-art high-resolution numerical weather prediction simulations and radar imagery for Sunday 13 January 2013, with a specific focus on the region of the Coonabarabran fire which started at around 1600 Eastern Daylight Time (EDT) on 12 January in the Warrumbungle National Park. The simulations show a complicated range of meteorology including weather features that would affect fire behaviour critical for fire-fighter safety.

Features such as convection outflow gust fronts are displayed in the simulations in the north-westerly wind ahead of the main wind change, together with boundary-layer rolls, and sea-breeze-like wind changes proceeding inland from the coast. In addition, small-scale vortices are modelled on the main change: these lead to hazardous local spikes in the modelled Forest Fire Danger Index. Exceptionally strong north/south temperature gradients were observed over inland New South Wales on the Sunday and these are also seen in the simulations.

Sunday 13 January brought difficult conditions for fire fighting. When the fire was declared {\textquotedblleft}out{\textquotedblright} on 24 January, it had burnt an area of 55,210 ha west of Coonabarabran, 53 homes, 131 other buildings and 95\% of the Warrumbungle National Park.

The simulation has been performed using the Australian Community Climate and Earth-System Simulator (ACCESS), and involves a sequence of nested limited area model runs embedded in the ACCESS global model run, with a finest grid spacing of 550 m. Our analysis will focus on how well the simulations capture the meteorological factors that promote extreme fire behaviour. The ACCESS model is used at the Bureau of Meteorology for operational numerical weather prediction, but is used here in research mode at resolutions much finer than current operational ones.

}, author = {Robert Fawcett and Yeo, Claire and W. Thurston and Jeffrey Kepert and KJ Tory} } @article {bnh-1963, title = {Simulating boundary-layer rolls with a numerical weather prediction model}, journal = {Quarterly Journal of the Royal Meteorological Society}, year = {2015}, pages = {1-14}, chapter = {1}, abstract = {

Boundary-layer rolls have an impact on bushfires, pollution dispersion, the triggering of extreme convective weather events, the air{\textendash}sea interaction and intensification of tropical cyclones and momentum, particle and gas fluxes. Previous numerical modelling studies that investigate the effects of boundarylayer rolls and the processes that control their dynamics have relied upon high-resolution, idealised simulations. Recently, however, numerical weather prediction (NWP) systems have increased in horizontal resolution to the point at which they are capable of explicitly resolving shallow convective circulations. Therefore, there is a need to assess the ability of NWP to accurately forecast the formation, development and breakup of boundary-layer rolls. Here, we assess the ability of the UK Met Office Unified Model (UM), the NWP component of the Australian Community Climate and Earth-System Simulator (ACCESS), to simulate the life cycle of boundary-layer rolls. A suite of simulations is performed, over a range of horizontal resolutions, of boundary-layer rolls observed across Victoria, Australia, on Black Saturday, 7th February 2009. In this case, it is found that a horizontal grid spacing of less than 0.6 km is required to adequately reproduce the scale and evolution of the observed rolls. We note that the boundary layer was particularly deep on this day and as a consequence the boundary-layer rolls were wider than may be typically observed, meaning the grid spacing specified here lies at the upper end of what would be required with a shallower boundary layer. The model output is used to assess how the boundary-layer rolls contribute to the high fire danger on Black Saturday. It is suggested that boundary-layer rolls may increase fire danger by (i) causing wind-direction variability at the surface, which increases the rate of spread of fires; and (ii) enhancing the process of long-range spotting by augmenting the vertical lofting of embers.

}, keywords = {Shallow convection; mesoscale modelling; high resolution NWP; terra incognita; Black Saturday bushfires; atmospheric boundary layer; wind direction variability}, url = {http://www.cawcr.gov.au/staff/jdk/Kepert_papers/Thurston_etal_2015_qjrms_acc.pdf}, author = {W. Thurston and Robert Fawcett and KJ Tory and Jeffrey Kepert} } @conference {bnh-2085, title = {The Sydney 2014 forecast demonstration project - a step from research to operations - non peer reviewed extended abstract}, booktitle = {Adelaide Conference 2015}, year = {2015}, address = {Adelaide, Australia}, abstract = {

Research proceedings from the Bushfire and Natural Hazards CRC \& AFAC Conference in Adelaide, 1-3 September 2015.\ 

}, author = {Michael Foley and Mika Peace and Deryn Griffiths and James Sofra and Jeffrey Kepert} } @article {bnh-1359, title = {Fire Danger Indices: Current Limitations and a Pathway to Better Indices}, number = {007}, year = {2014}, month = {12/2015}, institution = {Bushfire and Natural Hazards CRC}, abstract = {

Fire danger ratings in Australia currently rely heavily on McArthur{\textquoteright}s indices for forests and grasslands. Advances in fire and in meteorological science means that these indices do not adequately reflect current knowledge or recent technological advances. We now have the capability to provide information on fire danger at a much greater spatial and temporal resolution than previously, but do not fully utilise it. The indices are used for a wider range of purposes than originally envisaged, and growing societal expectations and changes in communication technology provide both the impetus and opportunity for a more detailed and more accurate service.

This report sets the agenda for fire danger policy and research into operations.

}, issn = {007}, author = {Yeo, Claire and Jeffrey Kepert and Hicks, Robin} } @proceedings {BF-4343, title = {Applications of Very High Resolution Atmospheric Modelling for Bushfires}, year = {2013}, url = {http://www.bushfirecrc.com/resources/research-report/applications-very-high-resolution-atmospheric-modelling-bushfires}, author = {Jeffrey Kepert and Robert Fawcett and KJ Tory and W. Thurston} } @article {BF-4282, title = {A comparison of the fire weather characteristics of the Melbourne dust storm (1983) and Black Saturday (2009): a high-resolution ACCESS case study}, journal = {20th International Congress on Modelling and Simulation}, year = {2013}, month = {12/2013}, pages = {167-172}, chapter = {167}, abstract = {We present the results of high-resolution simulations of the fire weather over Melbourne during its notorious dust storm on 8 February 1983. The simulations were performed using the Australian Community Climate and Earth-System Simulator (ACCESS), and involved a sequence of nested model runs starting with a global model run initialised with an ERA-Interim reanalysis initial condition. The ACCESS model is used at the Bureau of Meteorology for operational numerical weather prediction, but is used here in research mode at resolutions much finer than those currently used operationally. The day of the dust storm saw the passage of a significant cool change across Victoria, with many similarities in the simulations to that of Black Saturday (7 February 2009), against which we compare it. Wind changes such as these two can have a significant (and dangerous) impact on the behaviour of bushfires in southeast Australia, and their prediction forms an important component of fire weather prediction in this part of the country. While the wind change on 8 February 1983 was accompanied by some fire activity, that activity was much less than the major fire activity which accompanied the significant wind change eight days later on Ash Wednesday (16 February 1983). Why the dust storm wind change was not associated with severe fires, while those on Ash Wednesday and Black Saturday were, is a challenging question. Catastrophic fires are quite rare, whereas significant fire weather events that could potentially lead to catastrophic fires (if the non-meteorological prerequisites were to fall into place) are much more common and their study can lead to further understanding of the fire events.}, keywords = {Ash Wednesday, Black Saturday, Fire weather, Melbourne{\textquoteright}s dust storm, numerical weather prediction}, url = {http://www.mssanz.org.au/modsim2013/A3/fawcett.pdf}, author = {Robert Fawcett and Alan Wain and W. Thurston and Jeffrey Kepert and KJ Tory} } @proceedings {BF-4339, title = {The Eyre Peninsula Fire of 11 January 2005: an ACCESS case study}, year = {2013}, url = {http://www.bushfirecrc.com/resources/research-report/eyre-peninsula-fire-11-january-2005-access-case-study}, author = {Robert Fawcett and W. Thurston and Jeffrey Kepert and KJ Tory} } @conference {bnh-4115, title = {Large-eddy simulations of bushfire plumes in the turbulent atmospheric boundary layer}, booktitle = {20th International Congress on Modelling and Simulation}, year = {2013}, month = {12/2013}, address = {Adelaide}, abstract = {

Spot fires are a hazardous phenomenon which can lead to unpredictable fire behaviour and accelerated fire spread. Spot fires occur when firebrands are lofted into strong ambient winds and ignite new fires downwind. Anecdotal evidence suggests that this lofting and transport of firebrands can be responsible for the ignition of spot fires at large distances, up to tens of kilometres ahead of the fire front. A thorough knowledge of the potential for lofting from a fire is therefore desirable in order to accurately predict the fires rate of spread and coverage.

The extent to which firebrands are lofted and transported away from a fire is largely determined by both the intensity of the fire convective column and the strength of the ambient winds. Previous work on the response of fire plumes to background winds has principally relied on theoretical or highly idealised numerical models. Here we use high-resolution three-dimensional numerical simulations, performed with the UK Met Office Large-Eddy Model, to investigate the behaviour of bushfire plumes. We begin by simulating the dry, neutral atmospheric boundary layer for a range of wind speeds. Simulations are run to a quasi-steady state, ensuring that the flow displays realistic turbulence properties. Plumes are then produced by imposing a localised positive surface heat flux anomaly at the model surface. The sensitivity of the size, shape and intensity of the plume{\textquoteright}s updraft to the interaction between the plume and the turbulent atmospheric boundary layer is explored, with reference to the potential for spotting.

}, author = {W. Thurston and KJ Tory and Robert Fawcett and Jeffrey Kepert} }