Human Influence on Changes in Seasonal Extreme Precipitation Across Different Land Regions

Globally, extreme precipitation has intensified annually, but large uncertainties remain at regional and seasonal scales. Detection and attribution analysis based on observations, climate models, and an updated optimal fingerprinting method that extreme precipitation has intensified significantly in all four seasons during 1950–2018 across the Northern Hemisphere, particularly in mid-to-high latitudes, with anthropogenic greenhouse gases driving over 70% of observed trend. Moreover, weaker increase is observed in June-July-August (JJA) compared to colder seasons. In the Southern Hemisphere, changes are more regionally and seasonally dependent, with a decreasing trend in JJA and increases in the other seasons, but confidence is limited by sparse observational data coverage. Regionally, extreme precipitation has significantly decreased in southwestern and southern South America in December-January-February (DJF), largely attributed to combined external forcing. These findings highlight the complex and uneven changes in extreme precipitation across different regions and seasons.