Wave Climate Variability and Trends in Tuvalu Based on a 44-Year High-Resolution Wave Hindcast

Waves are one of the main causes of coastal flooding and shoreline change in low-lying atoll nations like Tuvalu. A detailed understanding of Tuvalu's wave climate is therefore critical for decision-makers, coastal engineers, and disaster-risk managers. Here, we investigate Tuvalu's wind-wave climate, changes due to large-scale climate variability, and long-term trends. A 44-year (1979-2022) high-resolution wave hindcast was developed using the unstructured version of the wave model Simulating Waves Nearshore (SWAN). The model resolution varied between 20 km offshore in deep water and 300 m close to shore. The model was forfed with the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) wind and boundary wave conditions. Northern and Southern Hemisphere winter months produced the largest and most powerful waves. Through the analysis of the directional wave energy spectra, we identified three main wave energy sources: (a) extratropical storms in the Southern Ocean; (b) extratropical storms in the North Pacific; and (c) easterly trade winds. Slightly positive trends in high-frequency (similar to 10 s) wave energy from the east and low-frequency (similar to 15 s) wave energy from the southwest were linked to an intensification of trade winds and an intensification and poleward displacement of the Southern Ocean storm belt over recent decades. The interannual variability of Tuvalu's wave climate was strongly linked to large-scale climate modes such as El Nino Southern Oscillation, Pacific Decadal Oscillation, and Arctic and Antarctic Oscillation. The study builds on previous research and significantly enhances the understanding of Tuvalu's wave climate variability. Plain Language Summary Waves are one of the main causes of coastal flooding and shoreline change in low-lying atoll nations like Tuvalu. A detailed understanding of Tuvalu's wave climate is therefore critical for decision-makers, coastal engineers, and disaster-risk managers. In this study, we investigate Tuvalu's wind-wave climate using a 44-year (1979-2022) high-resolution wave hindcast. A strong seasonality in significant wave height and wave power was found with Northern and Southern Hemisphere winter months producing the largest and most powerful waves. We identified three main wave energy sources: (a) extratropical storms in the Southern Ocean; (b) extratropical storms in the North Pacific; and (c) easterly trade winds. An intensification of the easterly trade winds, as well as an intensification and poleward shift of the Southern Ocean storm belt over recent decades resulted in slight positive trends in wave energy. The interannual variability of Tuvalu's wave climate was strongly linked to large-scale climate modes such as El Nino Southern Oscillation, Pacific Decadal Oscillation, and Arctic and Antarctic Oscillation. The study builds on previous research and enhances the understanding of Tuvalu's wave climate variability. The hindcast may be a useful tool to study other processes like long-term shoreline change.