Historical and possible future changes of wave heights in northern hemisphere oceans

Abstract

In this study, we review and extend previous studies on changes of wave heights, focusing on both observed and possible future changes in the North Atlantic and in the North Pacific. Two wave hindcasts are used here as observed waves for 1958– 1997: a global wave hindcast based on the 10-m winds taken from the NRA (i.e., the reanalysis of the National Centers for Environment Prediction, National Center for Atmospheric Research), and a detailed North Atlantic wave hindcast produced with intensively reanalyzed surface winds over the North Atlantic basin. The observed relationships between sea level pressure (SLP) and significant wave height (SWH) are used to construct climate change scenarios of SWH. Scenarios of seasonal mean SWH are constructed by means of redundancy analysis (RA), while projections of seasonal extreme SWH are made using nonstationary generalized extreme value (GEV) models. The RA and GEV models are trained using the NRA SLP and the observed SWH data for 1958–1997. The SWH scenarios are constructed using seasonal mean SLP and squared SLP gradient fields from a coupled climate model (CGCM2) under three different forcing scenarios. The projected (and observed) trends/changes in SWH are assessed by conducting a trend analysis, in which linear trends are evaluated against quadratic trends. Both oceans had significant changes in both winter and fall seasonal means and extremes of SWH during 1958–1997; they are also projected to have significant changes in the 21st century under all three forcing scenarios. The rate and sign of the projected future SWH changes are not constant throughout the 21st century; and in some regions, these appear to be quite dependant on the forcing conditions. Often, the projected SWH changes are characterized either by faster increases in the