Intensification of a European Storm Cluster in a Warmer Climate: Evidence from Regional Storylines

Abstract. In February 2022 a series of three extreme winter storms hit the coast of Northern Germany and Northwestern Europe. In this study, cyclones Ylenia, Zeynep and Antonia  were attributed to anthropogenic climate change, assessed through event-based storylines across five climate states: pre-industrial, present-time, +2K, +3K and +4K. The storylines vary only in sea surface temperatures and greenhouse gas concentrations, isolating the thermodynamic components of anthropogenic climate change. Global storylines were dynamically downscaled for Europe, focusing on Northwestern Germany and the German Bight. Spectral nudging was used to keep the large-scale weather patterns close to observations. Spectral nudging was turned off in a second step, which allows an assessment of dynamical effects beyond the thermodynamic ones. Anthropogenic warming amplified both wind speeds and precipitation during the February 2022 extra-tropical cyclone cluster, strengthening gradually from present-time to +4K warming and remaining robust across dynamical configurations, indicating systematically intensifying impacts on the analysed domain under continued warming. Changes in precipitation are more evident in northern regions of the analysed domain, with a notable precipitation increase in the Norwegian west coast. The changes in wind speed and precipitation are shown to possibly be related to changes in the storm tracks position, indicating a strong relationship with the large-scale circulation, even though only slightly changes were observed in jet stream position. Without spectral nudging, future storylines exhibit greater ensemble spread and a northward‑tilted storm track. Overall, the study found a gradual increase in areas with robust positive changes of wind speed and precipitation during the storm cluster in warmer climate states, with dynamical changes further amplifying the magnitude of already notable thermodynamic response, but evidencing the role of internal variability between storyline members in decreasing the spatial robustness.