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Quantifying mechanisms responsible for extreme coastal water levels and flooding during severe tropical cyclone Harold in Tonga, Southwest Pacific

Tu'uholoaki, Moleni and Espejo, Antonio and Wandres, Moritz and Singh, Awnesh M. and Damlamian, Herve and Begg, Zulfikar (2023) Quantifying mechanisms responsible for extreme coastal water levels and flooding during severe tropical cyclone Harold in Tonga, Southwest Pacific. Journal of Marine Science and Engineering, 11 (6). NA. ISSN 2077-1312

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Abstract

The South Pacific region is characterised by steep shelves and fringing coral reef islands. The lack of wide continental shelves that can dissipate waves makes Pacific Island countries vulnerable to large waves that can enhance extreme total water levels triggered by tropical cyclones (TCs). In this study, hindcasts of the waves and storm surge induced by severe TC Harold in 2020 on Tongatapu, Tonga’s capital island, were examined using the state-of-the-art hydrodynamic and wave models ADCIRC and SWAN. The contributions of winds, atmospheric pressure, waves, and wave-radiation-stress-induced setup to extreme total water levels were analysed by running the models separately and two-way coupled. The atmospheric pressure deficit contributed uniformly to the total water levels (~25%), while the wind surge was prominent over the shallow shelf (more than 75%). Wave setup became significant at locations with narrow fringing reefs on the western side (more than 75%). Tides were dominant on the leeward coasts of the island (50–75%). Storm surge obtained from the coupled run without tide was comparable with the observation. The wave contribution to extreme total water levels and inundation was analysed using XBEACH in non-hydrostatic mode. The model (XBEACH) was able to reproduce coastal inundation when compared to the observed satellite imagery after the event on a particular coastal segment severely impacted by coastal flooding induced by TC Harold. The coupled ADCIRC+SWAN underestimated total water levels nearshore on the reef flat and consequently inundation extent as infragravity waves and swash motion are not resolved by these models. The suite of models (ADCIRC+SWAN+XBEACH) used in this study can be used to support the Tonga Meteorological Service Tropical Cyclone Early Warning System.

Item Type: Journal Article
Subjects: Q Science > Q Science (General) > Q1-390 Science (General)
Q Science > QC Physics > QC1-75 General
Q Science > QC Physics > QC851-999 Meteorology. Climatology Including the earth's atmosphere
Q Science > QC Physics > QC980-999 Climatology and weather
Q Science > QC Physics > QC994.95-999 Weather forecasting
Divisions: Pacific Centre for Environment and Sustainable Development (PACE-SD)
Depositing User: Awnesh Singh
Date Deposited: 19 Jun 2023 00:18
Last Modified: 19 Jun 2023 00:18
URI: http://repository.usp.ac.fj/id/eprint/14048
UNSPECIFIED

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