The 2018 Tropical Cyclone Hazard Assessment (TCHA18) provides an evaluation of the likelihood and intensity (“how big and how often”) of the occurrence of tropical cyclone winds across the Australian region, covering mainland Australia, islands and adjacent waters. It is a probabilistic evaluation of the expected maximum gust wind speeds with a range of annual exceedance probabilities (or conversely, average recurrence intervals). The assessment is derived using a statistical-parametric model developed by Geoscience Australia called the Tropical Cyclone Risk Model (TCRM). Maximum 0.2-second duration, 10-metre above ground wind speeds are calculated for Standard Australia's AS/NZS 1170.2 (2011) terrain category 2 (0.02 m roughness length) surface conditions, over a 0.02 degree grid across Australia. Maps of average recurrence interval (ARI) wind speeds of 100- and 500-year ARI are provided in a separate product suite.

The region of coastal South East Queensland (SEQ) represents a large concentration of population, business activity and infrastructure important to the economy of Queensland and Australia. The region is also subject to severe storms that can generate damaging winds, particularly as a result of thunderstorm and tropical cyclone activity. Older residential homes have historically been the most damaged in such storms, contributing disproportionately to community risk, and recent storm damage in Western Australia has indicated that there are issues with modern SEQ homes also. This risk posed by severe wind is not well understood, nor are the optimal strategies for managing and potentially reducing this risk. Previous work has provided insights into the potential impacts of rare storm events in the SEQ region and the vulnerability of residential homes that contribute to them. The Severe Wind Hazard Assessment for Queensland (SWHAQ) project (Arthur, et al., 2021) provided valuable insights on the potential impacts of rare tropical cyclones making landfall in the region. The SWHA-Q project included two storms impacting the Gold Coast that highlighted that credible cyclone events in South East Queensland generating no more than design level wind gusts can have challenging consequences. Five tropical cyclone scenario events were selected by the project partners and modelled to provide a demonstration of the residential housing damage outcomes that could result from plausible storms that could impact South East Queensland. Four storms generated category 3 winds (gusts over 165 km/h) on landfall and were essentially design level events for ordinary residential structures. The fifth (Scenario 3) generated category 4 winds (gusts over 225 km/h) at landfall but was still quite a credible storm for the region. The events highlighted, as did the previous SWHA-Q work, that rare cyclone events of this kind affect all parts of the study region and produce very significant consequences. One design level event (Scenario 2) was found to inflict moderate or greater damage to 39% of the homes in the region, representing a major need for temporary accommodation. One of the events was used as the evidence-based scenario that underpinned Exercise Averruncus – A SEQ Tropical Cyclone Impact held in Brisbane on 15 June 2022 that explored critical issues around preparation for, response to, and initial recovery from the event. It is noted that the scale of impacts from any scenario is contingent on the characteristics of the TC itself (size, intensity, landfall location) and on the landscape in which buildings are located. However, while each scenario is unique, the suite of scenario impacts provide a useful resource for EM planning by local government, emergency services and other agencies with a role in disaster recovery.

The Tropical Cyclone Scenario Selector Tool (TC SST) provides an interactive application to interrogate the stochastic event catalogue which underpins the 2018 Tropical Cyclone Hazard Assessment (TCHA18). The application allows users to search for TC events in the catalogue based on location and intensity (either TC intensity category, or maximum wind speed), visualise the tracks and the wind fields of those events, and download the data for further analysis.

The northwest Australian coastline from Broome to Exmouth has experienced the greatest number of landfalling Tropical Cyclones (TCs) in Australia since records began in 1908 (Bureau of Meteorology, 2020). Despite this, direct impacts of a TC on individual communities are comparatively unusual, especially for severe TCs (category 3-5) as the coastline is sparsely populated. Communities are generally hundreds of kilometres apart, and a TC can cross the coast between them with little impact. However, the highest recorded wind gust in the world was 408 km/h (category 5) at Barrow Island during TC Olivia on 10 April 1996 (Courtney et al., 2012). The highest wind gust on the Australian mainland was 267 km/h (category 4) at Learmonth during TC Vance on 22 March 1999 (Australian Bureau of Meteorology, 2000). This emphasises the fact that no regional centre in WA, with the exception of Exmouth, has experienced a high-end TC impact in the past 30 years, but there is the potential for extreme events to strike these communities. While the impacts of past cyclone events have been well-documented, it is unlikely that communities have experienced the ‘worst-possible’ (either most intense or most damaging) cyclone impact in the past 30 years. To understand the scale of impacts that would occur if a TC were to make a direct impact on any of these communities the West Australian Department of Fire and Emergency Services (DFES) applied for funding through the Natural Disaster Resilience Program. In July 2017 funding was obtained to conduct the Severe Wind Hazard Assessment (SWHA) project. This initiative is aligned with the National Disaster Risk Reduction Framework (Department of Home Affairs, 2018), which outlines a national, comprehensive approach to proactively reducing disaster risk in Australia. To better understand the potential impacts of cyclones and extra-tropical transitioning cyclones on Western Australian communities, the project has modelled a number of scenarios to demonstrate the impacts of realistic, but perhaps not experienced, cyclones for Broome, Port Hedland, South Hedland and Wedgefield, Karratha, Dampier, Roebourne, Wickham and Point Samson, Exmouth, Carnarvon, Geraldton and Perth A consistent message that comes from this analysis is the excellent performance of modern residential construction to withstand the impacts of these scenario TCs. However, a house built to code’s performance is reliant on being maintained during its life so that its resilience is retained; just because a building was built to standard doesn’t mean it has been maintained to that standard. Investigations conducted into previous cyclones demonstrate that houses built pre-1980s (pre-code) under perform and offer lesser protection compared to those houses built to code post-1980s. In line with that the work undertaken in this report shows clearly that communities with a larger proportion of pre-code residential construction will suffer greater damage, due to the greater vulnerability of older building stock. Houses not originally built to current standards cannot, in general, be expected to perform to the current design levels, irrespective of the maintenance level. The only way to increase performance of these older residential buildings is to retrofit to modern standards. The analysis undertaken in the project has provided emergency managers from local, district and State level with a wealth of information on the potential impacts a major cyclone would have on Western Australia. This information has provided opportunity to strengthen planning processes and raise community awareness of mitigation actions that can reduce impacts. This collection comprises reporting and data developed as part of the Severe Wind Hazard Assessment for Western Australia. The collection includes all reports, publications (e.g. conference presentations, posters and news articles, etc.), and data delivered to Department of Fire and Emergency Services (Western Australia).

The TCHA18 Data collection covers the model output generated by the Tropical Cyclone Risk Model as part of the assessment. This includes average recurrence interval wind speeds, stochastic track catalogues, wind fields and intermediary data. It also includes an evaluation track catalogue, used to evaluate the performance of the model with respect to historical landfall rates, frequency and track density.

Natural hazard data supports the nation to respond effectively to emergencies, reduce the threat natural hazards pose to Australia¿s national interests and address issues relating to community safety, urban development, building design, climate change and insurance. A baseline understanding of hazards, impacts and risk can help to enhance community resilience to extreme events and a changing environment. Probabilistic hazard and risk information provides planners and designers opportunity to investigate the cost and benefit of policy options to mitigate natural hazard impacts. Modelled disaster scenario information can enable disaggregation of probabilistic hazard to identify the most probable event contributing to hazard. Tropical cyclone return period wind hazard maps developed using the Tropical Cyclone Risk Model. The hazard maps are derived from a catalogue of synthetic tropical cyclone events representing 10,000 years of activity. Annual maxima are evaluated from the catalogue and used to fit a generalised extreme value distribution at each grid point. Wind multipliers are factors that transform regional wind speed to local wind speed, mathematically describing the influences of terrain, shielding and topographic effects. Local wind speeds are critical to wind-related activities that include hazard and risk assessment. The complete dataset is comprised of: - Stochastic tracks, wind fields and impact data; - Probabilistic wind speed data (hazard); - Site-exposure wind multipliers.

In March 1999, TC Vance swept through Exmouth, with the eye wall of the cyclone passing directly over the township generating gusts to 267 km/h. Around 10% of residential houses showed structural failure, with some types of housing experiencing significantly greater damage. By revisiting the impacts of TC Vance, we hope to guide thinking of emergency managers and local government on planning for when another category 5 TC strikes Exmouth. Using the best track information provided by the Bureau of Meteorology, we simulate the wind field of TC Vance using Geoscience Australia’s Tropical Cyclone Risk Model (TCRM), incorporating the local effects of topography, terrain and shielding afforded by neighbouring structures. This simulation is validated against observations of peak wind speed recorded at Learmonth Airport and other regional weather stations. The impacts of TC Vance are calculated for the present building stock in Exmouth, which has grown by nearly a third since 1999. Modern residential buildings perform very well, in line with the performance levels established by the wind loading standards for the region. Some groups of older buildings – specifically the U.S. Navy block houses that survived TC Vance unscathed – also perform very well. The analysis shows the town of Exmouth would still suffer substantial impacts, with around 700 buildings likely to suffer moderate to complete damage. This translates to around 1400 people, with at least half of those requiring temporary accommodation in the days and weeks immediately after the cyclone. These types of analysis help to reduce uncertainty and enhances decision-making for emergency services, enabling a more proportional response for rescue, damage assessments and initial recovery at the State, regional and local levels. From a strategic perspective it can also be used to identify and verify current and future capability needs for agencies involved in managing the cyclone hazard. Presented at the Australian Meteorological and Oceanographic Society Annual Meeting and the International Conference on Tropical Meteorology and Oceanography (AMOS-ICTMO 2019) Conference

The 2018 Tropical Cyclone Hazard Assessment (TCHA18) provides an evaluation of the likelihood and intensity (“how big and how often”) of the occurrence of tropical cyclone (TC) winds across the Australian region, covering mainland Australia, islands and adjacent waters. It is a probabilistic evaluation of the expected maximum gust wind speeds generated by TCs, with a range of average recurrence intervals (ARIs) or conversely, average exceedance probabilities (AEPs). The TCHA18 provides hazard profiles (ARI versus wind speed) for over 400 locations in Australia and neighbouring regions, and a catalogue of synthetic TC events that can be used for scenario exercises. The TCHA18 also establishes a baseline for the understanding of TC hazard in the current climate against which projections of future TC wind hazard can be compared. We will demonstrate data access methods and applications of the TCHA18 for a range of users. A key component of the TCHA18 is the synthetic event catalogue that contains details of all events that informed the probabilistic assessment. The event catalogue can be interrogated by users to find TC events for more detailed modelling, leading to impact assessment studies. Presented at the Australian Meteorological and Oceanographic Society Annual Meeting and the International Conference on Tropical Meteorology and Oceanography (AMOS-ICTMO 2019) Conference

Tropical cyclone scenario prepared for Tonga National Emergency Management Office (NEMO) as part of the PacSAFE Project (2016-2018)

Tropical cyclone Gita impacted the Kingdom of Tonga in February 2018, causing significant damage across the main island of Tongatapu. This dataset is a best estimate of the maximum local gust wind speed across Tongatapu, based on the best-available track information, elevation and land cover data. The data represents the maximum 0.2 second, 10-metre above ground level wind speed at (approximately) 25 metre horizontal resolution. The wind field was generated using: Geoscience Australia's Tropical Cyclone Risk Model - https://github.com/GeoscienceAustralia/tcrm Wind Multipliers code - https://github.com/GeoscienceAusralia/Wind_Multipliers TC Gita track was sourced from the Joint Typhoon Warning Center (http://www.metoc.navy.mil/jtwc/jtwc.html)