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by Leslie Gordon and Curt Storlazzi

According to a report released in January 2015 by the U.S. Geological Survey (USGS), climate changes during the 21st century are expected to alter the highest waves and strongest winds across U.S. and U.S.-affiliated Pacific islands (see map, below).

Information on changes in waves and winds under global climate change is crucial for understanding the sustainability of existing infrastructure and natural and cultural resources. It is also critical for planning future investments, such as renewable wind and wave energy for islands, and for understanding the viability of coastal economic activities, such as fishing and tourism. Wave- and wind-driven processes drive flooding of coastal land, potentially damaging islands’ infrastructure, fresh-water supplies, and natural resources, and harming federally protected species such as nesting seabirds. Such impacts may only be exacerbated in the future by projected trends in sea-level rise.

“With little to no publicly available historical wind and wave data for most of the U.S.-affiliated Pacific islands, and no future projections of waves and winds for different climate scenarios, there was a great science and management need to understand how waves and wind might change in future climates,” said Curt Storlazzi, USGS oceanographer and lead author of the study.

Scientists from the USGS and the University of California, Santa Cruz (UCSC) ran four global climate models (developed for the Intergovernmental Panel on Climate Change), using them to drive a global-wave model to look at projected changes in wave height, wave period, wave direction, wind speed, and wind direction. They focused on three Hawaiian Islands and 22 other locations on U.S.-affiliated islands in the Pacific Ocean. Modeling results project that wind and wave patterns will change over the years throughout the century, and also over certain months and seasons within each year.  

“Natural-resource managers, communities, and engineers will all benefit by being able to prepare for the shifts in inundation risk shown by this study. This work shows that the degree of change we see will depend on how greenhouse-gas emissions change,” said Jeff Burgett, science coordinator for the Pacific Islands Climate Change Cooperative.

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Scientists first ran the models for the years 1976–2005 and compared the results to the few available historical instrumental data in order to make sure the models were functioning properly. Then they ran the models for two future time spans—mid-21st century (2026–2045) and end-of-21st century (2085–2100)—under two different climatic scenarios: increasing greenhouse-gas concentrations until mid century, followed by reduced emissions (known as scenario RCP4.5), and unfettered growth of emissions (scenario RCP8.5). (These RCPs, or “representative concentration pathways,” are two of four greenhouse-gas-concentration trajectories adopted by the Intergovernmental Panel on Climate Change for its Fifth Assessment Report.)

The spatial patterns and trends are mostly similar between the two different greenhouse gas concentration scenarios (scenario RCP4.5 and scenario RCP8.5), although the results of the study reveal some differences among islands. The magnitude and spatial extent of the trends are generally greater for the higher-emissions scenario (RCP8.5).

In general, extreme wave heights (the top 5 percent) are projected to increase from now until mid-21st century and then decrease toward the end of the 21st century. Peak wave periods (another measure of intensity) are forecast to increase east of the International Date Line and decrease west of the International Date Line. In equatorial Micronesia, extreme waves and winds are projected to undergo substantial (greater than 20 degrees) shifts in direction.

Detailed maps, graphs, and tables provided in the report will be useful to scientists, engineers, managers, community leaders, and others trying to understand and plan for the effects of climate change.

The full USGS Open-File Report 2015–1001, “Future Wave and Wind Projections for United States and United States-Affiliated Pacific Islands,” by Curt D. Storlazzi, James B. Shope, Li H. Erikson, Christie A. Hegermiller, and Patrick L. Barnard is available online. This research was supported by the Pacific Islands Climate Change Cooperative.