SWOT capabilities for measuring extreme coastal water levels

This study investigates the capabilities of the Surface Water and Ocean Topography (SWOT) satellite to observe and analyze storm surges, a major driver of extreme sea level events that result in devastating coastal flooding. Storm surges, caused by wind setup, the inverse barometer effect, and wave setup, lead to rapid sea level rises, as demonstrated in events like Storm Gloria in the Mediterranean and Hurricane Milton in the Gulf of Mexico. Traditionally, tide gauges (TGs) have been the primary tool for studying these phenomena. While TGs provide high-frequency data, they are sparsely distributed, fixed to shorelines, and unable to capture the full spatial footprint of storm surges in the open ocean or along complex coastlines. Satellite altimetry has advanced surge detection, but missions like TOPEX/Poseidon and Jason series are constrained by narrow ground tracks and large gaps, limiting their ability to resolve fine-scale surge dynamics.

The SWOT satellite, launched in December 2022, addresses these limitations with its innovative wide-swath interferometric radar, producing two-dimensional sea surface height (SSHA) maps at ~2x2 km resolution. This unprecedented capability is particularly valuable near coastlines, where traditional altimetry struggles due to land interference. SWOT’s ability to observe storm surges in two dimensions provides new opportunities to understand their spatial evolution. By combining SWOT data with TG observations, SCHISM hydrodynamic model, and ERA5 atmospheric reanalysis of wind and pressure fields, this study offers a comprehensive analysis of storm surge dynamics across diverse environments, including the Baltic Sea, North Sea, and regions frequently affected by tropical cyclones as Gulf of Mexico.

The results reveal that SWOT accurately captures the spatial footprint of storm surges and their evolution over time, with strong agreement between SWOT-derived sea level anomalies (SLA) and tide gauge records. Case studies demonstrate SWOT’s capability to monitor storm surges in micro-tidal, macro-tidal, and regions frequently impacted by tropical-cyclones, showcasing its adaptability to various oceanic regimes. SWOT’s high-resolution spatial data significantly enhance coastal hydrodynamic models by providing detailed observations in regions with sparse TG coverage. Unlike traditional altimeters, which provide isolated measurements along predefined tracks, SWOT delivers wide-swath snapshots that unveil the full structure of storm surges, offering a more comprehensive understanding of their dynamics.

This study underscores SWOT’s transformative potential for monitoring, forecasting, and mitigating storm surges. By bridging critical observational gaps and providing high-resolution spatial data, SWOT complements traditional altimetry and ground-based measurements, offering unprecedented tools to improve coastal resilience. Its contributions are particularly significant in the context of climate change, where more frequent and intense extreme sea level events threaten coastal populations and infrastructure. SWOT’s ability to advance our understanding of storm surge processes represents a major step forward in developing strategies to manage and mitigate the risks associated with extreme weather and rising seas.