| Author: | Bagnasco, Tiziano |
| Title: | A multi-scale investigation of waves in the South China Sea : integrating hindcasts, trend analysis, multifractal signatures, and nature-based solutions |
| Advisors: | Stocchino, Alessandro (CEE) |
| Degree: | Ph.D. |
| Year: | 2026 |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | 1 volume (various pagings) : color illustrations, maps |
| Language: | English |
| Abstract: | The South China Sea (SCS) is a region of critical economic and ecological importance, subject to complex wave climates influenced by monsoon systems and climate change. However, a comprehensive, holistic understanding of its wave dynamics, from basin-scale extremes to coastal interactions, is still needed. This thesis aims to provide a high-resolution, multi-scale characterization of wave processes in the SCS. It specifically investigates long-term trends in annual maximum wave heights, their underlying multifractal properties, and the efficacy of mangroves as a natural coastal defense. To achieve this, a two-way coupled wave-current high-resolution hindcast was developed for the SCS. A more specific treatment was reserved for typhoons and extreme events, that were simulated with the Holland parametric wind model. The hindcast data were then analyzed using a non-stationary extreme value approach to characterize significant wave height trends and for return level estimations. Moreover, a multifractal detrended fluctuation analysis (MF-DFA) was performed to the significant wave height series to uncover their scaling properties. Finally, the wave dissipation capacity of mangroves was quantified through a focused case study in the Mai Po Nature Reserve, Hong Kong. The results reveal a solid performance of the SCHISM-WWMIII model, with the wave-current coupled hindcast providing robust nearshore skills, enhanced by the Holland model for accurate typhoon peak HS and storm surge predictions. Non-stationary extreme value analysis identifies significant wave height trends, with most pronounced negative trends of about -0.045 m/year in northern and eastern SCS and positive trends up to around 0.019 m/year in southern regions, amplified by 20-30% during typhoon seasons, and 25-year return levels reaching 12 m in central-northwestern SCS, with projected increases by 2122. MF-DFA uncovers synoptic (10-21 days), seasonal (5-7 months), and inter-annual (1.4-1.7 years) time scales, with northern SCS showing super-persistence (Hurst exponents > 1.8) and southern regions greater stability. Mangrove dissipation at Mai Po reduces wave heights from 1.2-1.7 m offshore to centimeters inland, primarily due to the effects of a shallow bathymetry, indicating that the effects of vegetation are marginal. This research establishes a robust numerical framework and provides novel insights into the non-stationary and multiscale nature of SCS waves. The findings have direct implications for coastal hazard mitigation, climate adaptation planning, and the conservation of nature-based coastal defenses like mangrove ecosystems. |
| Rights: | All rights reserved |
| Access: | open access |
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