Spatial clustering of severe European winter windstorms on intra-seasonal timescales

European winter windstorms are one of the most damaging natural hazards in Europe, and when these severe windstorms cluster in time, economic losses and environmental damages are amplified. Our previous analysis on the behaviour of European winter (DJF) windstorms clustering on shorter intra-seasonal timescales revealed distinct intra-seasonal temporal behaviour, where, depending on location, two clear periods of enhanced clustering are identified, one at the middle and one at the end of the season. Here, we investigate the spatial development characteristics of these cyclones (associated with the windstorms) and examine their intra-seasonal variation. To cluster cyclones with similar spatial development characteristics, we first applied dimension reduction via PCA to ERA5 1000 hPa 3-day development fields, then performed k-means cluster analysis as in Leckebusch et al. (2008b).

K-means ‘primary storm clusters’ that contain the highest relative frequency of European windstorms are identified. Further investigation of these primary storm clusters reveals 5 primary storm clusters that show distinct spatially varying windstorm footprint occurrences, which have resulted from a similar grouping of 3-day development fields. For example, among these 5 primary storm clusters, we can make distinctions between the 3-day development fields more likely to give rise to windstorms over Western Central Europe vs Scandinavia. We also reveal depending on the time within the winter season, certain k-clusters contribute more than others, specifically during the 2 periods of enhanced temporal clustering.