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Mayer, Julia

University of British Columbia

Tarawa Atoll (Republic of Kiribati), located in the Central Pacific Ocean near the equator, is exposed to significant sea level and wave variability due to the El Niño / Southern Oscillation (ENSO) cycle. As significant wave height (Hs) and energy play a crucial role in inundation events, this thesis investigates ENSO’s impact on wave activity by analyzing the full offshore wave energy spectrum of two wave hindcasts between 1979 and 2018. When assessing the granularity needed to study an atoll’s wave variability, the high-resolution hindcast provided by the Pacific Community more accurately represented wave variations near the shorelines but underrepresented extreme waves compared to the hindcast acquired from the Collaboration for Australian Weather and Climate Research. The analysis focussed on the distinct effects of Central Pacific (CP), Eastern Pacific (EP), and mixed El Niño events, all exhibiting an overall directional change with increased wave energy due to trade wind changes and westerly wind bursts. During the boreal winter of EP El Niño events, positive anomalies were observed in waves originating from the north and northeast, predominantly approaching Tarawa’s less densely populated shorelines. Similarly, La Niña conditions exhibited increased wave activity from the east. South Tarawa’s densely populated lagoon-facing shorelines however were mainly impacted during CP and mixed El Niño events. By clustering extreme wave events, I found these to be more frequent during El Niño conditions, due in part to the higher likelihood of westerly wind bursts. Subsequently, I used Sheppard et al.’s (2005) wave attenuation model to estimate the propagation of average and extreme waves across the reef flat, revealing that the western lagoon-facing shoreline, typically characterized by reduced wave energy and wave set-up, is particularly susceptible to wind-generated waves during El Niño. The model runs also encompassed the potential impact of future sea level rise and reef degradation, providing a sensitivity analysis of how these forces will potentially act together in the future. By 2100, Hs along Tarawa’s lagoon-facing shoreline during El Niño-related westerly wind bursts is projected to increase by up to 89% and more than triple in wave energy under the SSP5-8.5 emission scenario.

Text

2023-12-08

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86850

Geography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/