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

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.

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

The local wind multiplier data for Tongatapu is used to generate local wind speeds over the island of Tongatapu, Tonga.

This wind field was produced within v2.0 of TCRM, using data from the Bureau of Meteorology to constrain the wind field. Wind multipliers were calculated using a landcover dataset derived from Landsat and Digital Earth Australia. This wind field may be refined in the future as new data becomes available. This record includes - the track data from the Bureau of Meteorology used to model Tropical Cyclone Debbie - the landcover dataset produced for the Airlie Beach region - the preliminary local wind field

Geoscience Australia has produced a National Tropical Cyclone Hazard Assessment (TCHA18). The 1%/0.2% Annual Exceedance Probability Maps provides 0.2-second duration, 10-metre above ground level gust wind speeds across Australia arising from tropical cyclone events over a 2-km grid, for 1% and 0.2% annual exceedance probability (100- and 500-year annual recurrence interval respectively). Surface conditions are assumed to correspond to terrain category 2 conditions as defined in AS/NZS 1170.2 (2011).

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.

This dataset provides an assessment of the tropical cyclone wind hazard for the Kingdom of Tonga. The data was generated to provide a collection of scenarios for detailed impact mapping as part of the PacSAFE project (2016-2018), funded by the Australian Department of Foreign Affairs and Trade. The dataset includes a catalogue of synthetic tropical cyclone tracks and the corresponding maximum wind swaths, average recurrence interval (ARI) wind speeds for ARIs from 5 to 10,000 years, and hazard profiles for selected locations within the simulation domain.

The Tropical Cyclone Scenario Selection tool enables users (e.g. emergency managers, engineers, researchers, etc.) to query the catalogue of tropical cyclone scenarios, developed as part of the 2018 Tropical Cyclone Hazard Assessment (TCHA18). The TCHA18 catalogue is comprised of 10,000 simulated years of tropical cyclone activity in the Australian region, amounting to over 160,000 tropical cyclone events. Using the search tools, the tracks and wind fields of individual events affecting a location or region can be discovered and explored. The returned scenarios are retrieved from a catalogue of synthetic tropical cyclones and can queried within the map and/or downloaded in various formats for follow-on 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).