@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-8124, title = {A characterisation of synoptic weather features often associated with extreme events in southeast Australia: Stage 1 {\textendash} common features of recent events}, number = {679}, year = {2021}, month = {07/2021}, institution = {Bushfire and Natural Hazards CRC}, address = {MELBOURNE}, abstract = {

Negatively tilted upper-tropospheric troughs are a synoptic weather pattern that have been associated with the development of thunderstorms and severe weather, including extreme fire weather and tornadoes. While various case studies and some preliminary climatological analysis have been conducted in the past, a thorough investigation of the development of these synoptic features during extreme weather events has not yet been done in Australia or elsewhere. This study aimed to identify how often negatively tilted troughs occur and how often they are associated with extreme storms and fire weather.

The objectives of the project were to:

The major components of the project were:

Review of previously documented cases

January 2003 Canberra fires

July 2014 Perth tornadoes

Climatology

While modern numerical weather prediction (NWP) systems are increasingly capable of resolving the surface weather parameters associated with severe weather events, there are known deficiencies. An example of this is the over-estimation of low winds and under-estimation of high winds common to numerous models. Better understanding of the role of features such as NTT in generating surface weather helps interpretation and refinement of the NWP output, particularly for users of weather data such as emergency services agencies.

Furthermore, as products from NWP such as sub-seasonal to seasonal outlooks become more refined, there is value in recognising the occurrence of potential impacts of NTT that may be resolved at the synoptic or sub-synoptic scale in such model configurations even if the potential severity of the weather parameters are note explicitly resolved. For example, if a sub-seasonal to seasonal model ensemble shows a high probability of a NTT occurrence in a particular region a certain number of weeks in advance, that is useful information for planning and preparedness for emergency services managers.

Thus, this sort of synoptic climatological study in combination with detailed analyses of particular events continues to be of great relevance to natural hazard prediction and management.

Future work

}, keywords = {exterme events, features, Fire, southeast Australia, synoptic, tornado, weather}, issn = {679}, author = {Love, P. and Paul Fox-Hughes and Remenyi, T. and Nick Earl and Dean Rollins and Gabi Mocatta and Rebecca Harris} } @conference {bnh-8275, title = {Long-range fire weather predictions developed and service established as new capability for Australia}, booktitle = {AFAC21}, year = {2021}, month = {10/2021}, publisher = {AFAC}, organization = {AFAC}, address = {Online}, abstract = {

Factors providing long-range predictability for this system include the pre-existing moisture content of vegetation (using agricultural drought measures), large-scale modes of variability (e.g., El Nino), sudden stratospheric warmings (e.g., polar vortex variations contributed to the severity of the 2019/20 summer) and long-term climate change.

The guidance products were designed with a user-driven approach, based on strong end-user engagement throughout the project. These long-range predictions are part of broader efforts to deliver seamless guidance over a wide range of time scales. Fire weather predictions and data are now available in a consistent form for long-range predictions out to several months ahead, historical records back to 1950 and future climate projections throughout this century. A seamless service across different time scales is intended to enhance planning capabilities from short to long time-scales, leading to enhanced resilience and disaster risk reduction for natural hazards. These fire weather outlooks have been described as a step change in improved capability, developed through user engagement, including for supporting risk reduction in prescribed burning and operational planning requirements.

}, keywords = {Capability, Fire, predictions, weather}, url = {https://www.afac.com.au/events/proceedings/06-10-21/article/long-range-fire-weather-predictions-developed-and-service-established-as-new-capability-for-australia}, author = {Dowdy, Andrew J} } @inbook {bnh-7841, title = {Sensing bushfire: Exploring shifting perspectives as hazard moves through the landscape}, booktitle = {Weather: Spaces, Mobilities and Affects}, year = {2020}, publisher = {Routledge}, organization = {Routledge}, chapter = {12}, abstract = {

Bushfires are an enduring part of the Australian landscape. While much research has explored community preparations and responses to disasters, there is little understanding of sensory engagements with hazards. In this chapter, we explore interviews with residents who had recently experienced a bushfire in Tathra, a small seaside town in south-eastern Australia. These interviews contain rich details of the sounds of the wind and fire and the smell of smoke inter alia that constitute embodied and sensory engagements with the bushfire. We focus on these bodily experiences to rethink the mobilities of people, boundaries and hazard {\textquoteleft}events{\textquoteright}. We suggest that a focus on sensory experiences of hazards provides a fuller understanding of more-than-human (im)mobilities and the continual becoming of place.

}, keywords = {affects, Bushfire, mobilities, sensing, space, weather}, issn = {9780367406394}, url = {https://www.routledge.com/Weather-Spaces-Mobilities-and-Affects/Barry-Borovnik-Edensor/p/book/9780367406394}, author = {Katharine Haynes and Matalena Tofa and Joshua McLaren} }