Extratropical cyclone clustering amplifies extreme sea-level rise around the North Sea

Understanding how extratropical cyclones contribute to extreme sea level (ESL) events is essential for assessing long-term coastal hazards. While individual cyclone impacts are well-documented, the role of cyclone clustering—i.e., multiple storms occurring within short time windows—remains underexplored. Here we present a comprehensive assessment of the relationship between cyclone clustering and ESL variability along the North Sea coast from 1940 to 2024.

We construct a dataset of cyclone life cycles using 3-hourly ERA5 reanalysis and identify clustered events based on consistent spatial and temporal proximity criteria. Concurrently, we analyze tide gauge records from stations surrounding the North Sea coast, applying detrending and band-pass filters to remove long-term and tidal signals to isolate storm-driven sea level variations.

Our results show that cyclone clusters predominantly occur in winter and have increased significantly in frequency over the past 85 years. Comparing sea level responses during clustered and non-clustered periods reveals that clustering events are associated with markedly higher positive sea level anomalies. These differences are especially pronounced in the upper extremes, indicating that clustering enhances the risk of compound ESL events beyond what is observed during non-clustered periods.

This work provides novel evidence that cyclone clustering plays a growing role in shaping extreme sea level behavior in the North Sea region. Our results also underscore the need to incorporate clustering metrics into coastal impact assessments, particularly under changing climate conditions.