Different Modes of Wave Response over the Past Four Decades: Coastal vs. Open-Ocean Regions

Tropical cyclone-induced waves (TCWs) are projected to intensify under global warming, with recent evidence suggesting that their growth outpaces the increase in surface winds. Yet, how TCWs differ between coastal and open-ocean environments remains poorly understood. Here, we investigate TCW characteristics during two climatic periods (1979–2000 and 2001–2023) using a coupled analysis of buoy observations and ERA5 reanalysis. Our results reveal a striking contrast: while open-ocean TCWs exhibited a pronounced intensification of up to 19% (~74 cm) over the past four decades, coastal TCWs show only a muted increase of 26 cm (~8%). This discrepancy is primarily linked to weaker wind forcing and a contraction of effective fetch in coastal regions. On a broader scale, global wave heights (GWs) demonstrate strong temporal and regional variability. The 1979–2000 period featured widespread increases exceeding 10 cm per decade, whereas 2001–2023 displayed pronounced regional disparities, with declines in the Pacific and Indian Oceans but increases in the North Atlantic, Southern Ocean, and Arctic. Notably, the Arctic exhibits a significant rise in extreme wave heights, consistent with reduced ice cover and enhanced wind-driven fetch, highlighting critical feedback to global warming. These findings underscore the importance of distinguishing coastal from open-ocean wave responses when assessing future hazards. By revealing the divergent trajectories of TCWs and GWs under climate change, our study provides a refined framework for understanding storm-induced risks and for improving projections of wave-driven coastal impacts.