Abstract:
Projected wave climate trends from WAVEWATCH3 model output were used as input for nearshore wave models (for example, SWAN) for the main Hawaiian Islands to derive data and statistical measures (mean and top 5 percent values) of wave height, wave period, and wave direction for the recent past (1996-2005) and future projections (2026-2045 and 2085-2100).
Three-hourly global climate model (GCM) wind speed and wind direction output from four different GCMs provided by the Coupled Model Inter-Comparison Project, phase 5 (CMIP5), were used as boundary conditions to the physics-based WAVEWATCH3 numerical wave model for the area encompassing the main Hawaiian islands. Two climate change scenarios for each of the four GCMs were run: the representative concentration pathway (RCP)-4.5 and RCP-8.5, representing a medium mitigation and a high emissions scenario, respectively. Simulation timeframes were limited to the years 2026-2045 and 2085-2100, as prescribed by the CMIP5 modeling framework.
The WAVEWATCH3 modeled deep-water wave heights, wave periods, and wave directions, with current bathymetry were used as boundary conditions to drive simulations of mean and top 5 percent wave conditions at higher resolution over the insular shelves of the main Hawaiian islands using the 3rd-generation SWAN wave model. For each scenario, 12 simulations were made representing the month-averaged or top 5 percent conditions. The SWAN model is based on discrete spectral action balance equations, computing the evolution of random, short-crested waves. Physical processes such as bottom friction and depth induced breaking, and, non-linear quadruplet and triad wave-wave interactions are included. Wave propagation, growth, and decay are solved periodically throughout the model grid. The SWAN model has been shown to accurately model the propagation and breaking of waves over Pacific coral reefs.
Purpose:
Changes in future wave climates in the tropical Pacific Ocean from global climate change are not well understood. Spatially and temporally varying waves dominate coastal morphology and ecosystem structure of the islands throughout the tropical Pacific. Waves also impact coastal infrastructure, natural and cultural resources, and coastal-related economic activities of the islands. Whereas scientific understanding of the dominant processes controlling coastal morphology and coastal and marine ecosystem structure on islands has improved over the past decade, our understanding of the linkages between these factors and variations in the wave climate across the Pacific is limited. Furthermore, the influence of global climate change on wind and wave conditions is not well understood. Stationary statistical approaches (such as return values) have typically been used to predict future extreme and mean wind and wave conditions, but with the changing climate this may not be a valid approach. Although some nonstationary statistical approaches (for example, nonstationary generalized extreme values) may sufficiently capture the variations and changes, recent work seems to point in the direction that the current climate alone cannot be used to estimate future conditions.
Information on potential changes in wave climate under future global climate change scenarios is therefore crucial to understanding not only the sustainability of existing infrastructure, natural, and cultural resources, but also planning for future investments in infrastructure and the viability of coastal-related economic activities such as fishing and tourism.
Supplemental_Information:
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