Future wave climate in nearshore California: new insights into the need for nearshore projections in local coastal hazard assessments

Abstract:

Wave action is one of the most important drivers of coastal impacts contributing to flooding and erosion. However, wave climate is highly variable across temporal and spatial scales. As amply evidenced in California, events like El-Niño, through their influence in extreme storms and mean oceanographic conditions, have drastic consequences on the magnitude, frequency, and locations of coastal impacts. To understand and predict future impacts, we require accurate nearshore characterization of wave action. However, most of our knowledge of future changes in the wave climate has been limited to offshore data whereas local, shallow-water changes remain less attended. In this study, we develop a new approach and datasets of nearshore wave climate for California’s coast that includes a multi-platform set of historic hindcast (ERA5, GOW, GCMs-Hindcast) and future mid- and end- century projections. We use this new data to report, for the first time, significantly different changes in the coastal wave climate compared to the previously found small changes in the offshore climate. The study analyzes both changes in the regular and extreme events. For example, we find that wave energy will vary between -40% to +45% by mid-century, compared to negligible changes in the offshore wave climate. These results indicate that the assumption that we can infer nearshore changes from offshore analyses, as commonly applied in climate change impact assessments, is no longer valid. Furthermore, we find that the future wave climate will surprisingly resemble the effect of El Niño on wave heights and periods. These results therefore provide new understanding of what impacts we could expect and have implications for preparatory actions as beach and cliff erosion as well as coastal flooding will be directly linked to the future local wave climate. This analysis provides important new insights for coastal adaptation planning in cities and counties across California, but also elsewhere.