A global analysis of extreme coastal water levels with implications for potential coastal overtopping

TLDR

Climate change and anthropogenic pressures are widely expected to exacerbate coastal hazards such as episodic coastal flooding. The study aims to estimate global potential coastal overtopping by incorporating sea‑level rise, storm surge, and wave runup at exposed open coasts. The authors employ a global model that integrates sea‑level rise, storm surge, and wave runup to calculate overtopping estimates. Annual overtopping hours have risen ~50% over the past two decades, are projected to accelerate faster than sea‑level rise, and could increase up to 50 times by the end of the 21st century under RCP 8.5, exposing more regions to overtopping.

Abstract

Abstract Climate change and anthropogenic pressures are widely expected to exacerbate coastal hazards such as episodic coastal flooding. This study presents global-scale potential coastal overtopping estimates, which account for not only the effects of sea level rise and storm surge, but also for wave runup at exposed open coasts. Here we find that the globally aggregated annual overtopping hours have increased by almost 50% over the last two decades. A first-pass future assessment indicates that globally aggregated annual overtopping hours will accelerate faster than the global mean sea-level rise itself, with a clearly discernible increase occurring around mid-century regardless of climate scenario. Under RCP 8.5, the globally aggregated annual overtopping hours by the end of the 21 st -century is projected to be up to 50 times larger compared to present-day. As sea level continues to rise, more regions around the world are projected to become exposed to coastal overtopping.