Four decades of hindcasts reveal intensification, seasonal shifts, and changing drivers of storm surge extremes in Northern and Western Alaska.

The evolving coastal flood hazards in the Arctic remain poorly categorized due to sparse observations, leaving it unclear when and where storm-driven water levels are intensifying or what physical processes drive them. Here we use a 45-year hydrodynamic hindcast of storm-driven water levels across Northern and Western Alaska (Bering, Chukchi, and Beaufort Sea coastlines), validated against coastal water level observations with a mean uncertainty of 0.2 m, to quantify the shifts in extreme event frequency and magnitude, identifying turning points in long-term surge trends, and attribute them to evolving atmospheric and cryospheric drivers. Model validation against statistically significant turning points occur across all major seas, with return levels of the storm driven water levels increasing by up to 30% in the Bering Sea and 10-20% in the Chukchi and Beaufort Seas. Seasonal analyses reveal intensification during late fall and winter, extending the hazard window into early winter months. Attribution analysis of the environmental drivers revealed that before the turning point, sea ice exerted the greatest influence on water levels (∼60%), with 10 m wind and sea level pressure playing smaller roles. After the turning point, the influence of sea ice declined (<50%), while wind and pressure together increased in importance (from ∼25% to ∼45%). Our results show that the compounding effects of the changing environment in the Arctic exacerbate storm-driven water levels.