Extreme sea-level events occur across a range of temporal and spatial scales, including high-frequency oscillations (periods T < 2 h). However, most research uses hourly or daily data and neglects higher-frequency processes such as seiches and meteotsunamis. This study investigates the characteristics of high-frequency (HF) sea-level extremes along the North Sea coast. Long-term (1993–2025) measurements were analysed from 29 tide gauges. After quality control, the astronomical tide was removed to isolate residuals, which were decomposed into low-frequency (T > 2 h) and high-frequency (T < 2 h) components. Next, extremes were extracted from the HF signal alone (HF extremes) and from the residual (residual extremes). Clustering techniques (K-medoids with Dynamic-Time-Warping and Euclidean distances) were applied to HF extremes to classify event types and identify regional patterns. HF extremes were grouped into six event types, and selected stations yielded five spatial clusters. Each event type was characterised by period, intensity, and its relationship to residual extremes. HF extremes were generally low compared with tidal ranges, and compound events (i.e., events in which an HF extreme coincided with a residual extreme) were infrequent (12.2% of HF extremes on average). Nevertheless, during compound events, alignment of HF and residual peaks substantially amplified sea levels. Spatial patterns highlighted the most intense events along the Dutch coast (IJmuiden Buitenhaven, Scheveningen, Brouwershavensche Gat, and Terschelling). These results were influenced by differences in local environmental conditions and sampling. Therefore, this study advances understanding of HF sea-level variability and compound events along the North Sea coast, supporting improved coastal hazard assessments.

Extreme sea level events pose significant risks to coastal regions, with non-tidal residuals (NTRs) being a primary driver in low-lying areas like the Netherlands, where shallow seas amplify their impact. This study investigates the spatial patterns of NTRs along the Dutch coast using time series clustering on historical NTR hydrographs. The design of hydraulic boundary conditions divides the Netherlands into three coastal regions. To evaluate whether this division sufficiently captures regional variability, three clustering scenarios (k = 3, k = 4, and k = 5) were explored. The analysis identified k = 5 as the optimal configuration based on the Davies-Bouldin index. This result emphasized the importance of fine-scale approaches to understanding regional spatial variations in NTR dynamics. Regional bathymetry and tide-surge interactions were explored as drivers of these spatial patterns. Southern stations near river systems and deeper waters displayed characteristics distinct from northern stations in the Wadden Sea, which are influenced by shallow tidal flats. Analysis of the M2 tidal constituent and the timing of NTR maxima relative to high tides underscored the role of tidal dynamics in shaping spatial clusters. Future research will focus on integrating spatio-temporal patterns and environmental drivers into clustering methodologies, providing deeper insights for coastal risk management and adaptation strategies.

Meteorological tsunamis (i.e., tsunami-like waves of atmospheric origin) are regularly observed in the Mediterranean Sea. During a single event, destructive flooding usually occurs in one location or limited area. However, in May 2021 and June 2022, strong meteotsunamis hit several Mediterranean locations up to 500 km apart. In the morning hours of the 24^th of May 2021, a meteotsunami hit Bonifacio on the island of Corsica (western Mediterranean, France) and in the afternoon hours of the same day, another meteotsunami hit Široka Bay on the island of Ist (Adriatic Sea, Croatia), 500 km away. About 13 months later, on the 26^th of June 2022, a meteotsunami hit Ciutadella on the island of Menorca (Spain) and two days later Bonifacio, 400 km away. Sea-level and atmospheric pressure data and satellite imagery, as well as synoptic conditions, associated with both events were analysed in detail. It has been confirmed that in the Mediterranean, meteotsunamis occur when meteotsunamigenic synoptic conditions prevail over the area, with a strong southwesterly jet stream embedded in dynamically or convectively unstable atmospheric layers standing out as the most important condition. The mete-otsunamigenic potential of each of the three bays (Ciutadella, Bonifacio, Širo-ka Bay) was investigated by considering: (1) the potential for Proudman resonance on the shelves offshore of the bays, (2) the orientation of the mouth of the bay and (3) the frequency of meteotsunamigenic synoptic conditions over the area. The strongest and most frequent meteotsunamis occur at locations where the shelf characteristics (width, depth, orientation), bay mouth orientation and distribution of general synoptic conditions, have characteristics that support the amplification of long-ocean waves and their propagation toward the bay mouth.