Global Precipitation Regimes and Seasonal Dynamics from IMERG Climatology: Focus on Europe and Italy

The accurate characterization of global precipitation regimes, encompassing not only the mean quantities but also the seasonal structure, concentration, and spatial heterogeneity, is essential for understanding the hydroclimatological dynamics and supporting climate-sensitive applications. This study presents a multi-scale precipitation climatology based on the IMERG Final Run V06B dataset (2001–2021) integrating satellite-derived monthly precipitation fields, unsupervised K-means clustering, Walsh–Lawler concentration metrics, and pixel-scale regime-dynamics indicators. The analysis identifies eight physically interpretable global precipitation regimes and six Italian sub-regional regimes characterized by distinct seasonal structures and precipitation persistence patterns. The resulting classifications exhibit a strong consistency with major atmospheric circulation domains, including monsoonal, mediterranean, continental, and equatorial precipitation regimes. A Hovmöller diagram highlights the seasonal northward migration of the Intertropical Convergence Zone (ITCZ) from approximately 5° S in January to 10° N in August. The K-means classification identifies eight physically interpretable global regimes, including a perhumid equatorial regime, a South-Asian monsoonal regime, a Southern-Hemisphere Mediterranean type, and a transitional autumn-peaked Mediterranean–Atlantic regime covering most of Italy and the broader Mediterranean basin. At the Italian scale, a dedicated K = 6 clustering reveals six distinct precipitation regimes, characterized by contrasting seasonal structures: the Alpine Convective regime, unique to the Alps and pre-Alpine foothills; the Po Valley Padano regime, the least seasonal regime in Italy; the Apennine Hybrid; the Tyrrhenian Mediterranean; the Adriatic Transition; and the Semi-arid Mediterranean regime, dominant across Sicily, Sardinia, and coastal southern Italy. The Walsh–Lawler Concentration Index increases markedly from north to south (~0.58), indicating a pronounced intensification of the temporal concentration of precipitation toward the Mediterranean climatic extreme. Overall, the study demonstrates the capability of high-resolution satellite climatologies to identify dynamically coherent precipitation-regime structures across multiple spatial scales and provides a quantitative baseline for future applications in hydrology, climate-risk assessment, and climate-change impact analysis.