Seasonal Classification of Large-Scale Atmospheric Circulation and Associated Precipitation Variability over Greece

This study examines the relationship between large-scale atmospheric circulation and precipitation variability over Greece, with a focus on both mean and extreme conditions. Seasonal mean sea level pressure anomalies over the Mediterranean are analysed using Principal Component Analysis with varimax rotation, followed by k-means clustering to identify dominant circulation patterns. The analysis is performed separately for each season over the period 1980–2025 using ERA5 reanalysis data. The identified circulation types are linked to precipitation over Greece through spatial composites and quantitative metrics, including seasonal precipitation totals and the maximum daily precipitation. The results reveal distinct spatial precipitation patterns associated with each circulation type, with cyclonic conditions favouring enhanced and widespread precipitation, particularly over western Greece, and anticyclonic types leading to suppressed rainfall. Despite relatively small differences in mean extreme precipitation intensity, substantial variations are observed in the upper tail of the distribution, with specific circulation types associated with a higher potential for intense daily rainfall events. This highlights differences between widespread precipitation and locally intense extremes, reflecting the role of circulation in modulating both the spatial extent and intensity of rainfall. The findings show that large-scale atmospheric circulation plays an important role in precipitation variability and extremes over Greece, particularly during the wet seasons, while summer precipitation appears to be more strongly influenced by local and convective processes.