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.

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

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)

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

The collection of products released for the 2018 National Tropical Cyclone Hazard Assessment (TCHA18). - 2018 National Tropical Cyclone Hazard Assessment - 2018 National Tropical Cyclone Hazard Assessment Stochastic Event Catalogue - 2018 National Tropical Cyclone Hazard Assessment Hazard Map - Tropical Cyclone Risk Model

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

The National Hazard Impact Risk Service for Tropical Cyclone Event Impact provides information on the potential impact to residential separate houses due to severe winds. The information is derived from Bureau of Meteorology tropical cyclone forecast tracks, in combination with building location and attributes from the National Exposure Information System and vulnerability models to define the level of impact. Impact data is aggregated to Statistical Area Level 1, categorised into five qualitative levels of impact.

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.

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.