Intra-seasonal variability of temporal clustering of European winter windstorms

Severe European winter windstorms are one of the most damaging natural hazards and thus a major threat to societies. Clustered European winter windstorms, storms that occur in quick succession over a specific period of time over a fixed location, can result in amplified structural and environmental damage and accumulated losses. Yet, variability of storm clustering on intra-seasonal timescales has not been fully investigated. We analyse winters (DJF) for the period 1981-2016 from ERA5 reanalysis, where tracks and storm impact footprints are identified through the impact-oriented wind-based tracking algorithm WiTRACK.  

We quantify the magnitude of clustering using the widely employed dispersion statistic as used in Mailier et al. (2006). The spatial distribution of clustering on 45- and 30-day timescales as well as the time development of clustering on even shorter 30-, 20-, 15- and 11-days reference periods are investigated. Thus, in a seamless approach from seasonal to synoptic clustering. Results from both windstorm clustering of tracks and the storm footprints will be presented. Preliminary findings suggest an increase in clustering occurrence in the later half of the winter season on 45- and 30-day timescales.  On shorter timescales (<30 days), depending on location, distinct periods of increased clustering e.g., in the middle and the end of the season can be identified.