Extreme rainfall seasonality plays a critical role in vegetation growth, agricultural production, and water resource management. Under global warming, increasing attention has been paid to its seasonal shifts and nonstationarity characteristics. In our comprehensive research, we utilized daily precipitation data from approximately 2200 gauge stations across China to investigate the spatial patterns, interannual variability, and long-term changes in the seasonality characteristics of annual maximum daily precipitation from 1960 to 2018. In the northern river basins, such as Hai, Songliao, Yellow, and Northwest River Basins, extreme daily events exhibit lower magnitude but stronger seasonality, accompanied by later timing and less variability in the mean date. Conversely, the southern river basins, such as Yangtze, Pearl, and Southeast River Basins, display the opposite pattern. Trend analysis shows that the mean occurrence date of extreme precipitation has generally advanced across most basins. Changes in the seasonality index reveal a clear north–south contrast: in the northern basins, seasonality has weakened, implying that extreme precipitation events become more dispersed throughout the year. In the southern basins, seasonality has strengthened, with extreme precipitation becoming more concentrated. The seasonal pattern of total column water vapor partly explains the earlier timing of extremes, especially in northern and central regions. Notably, El Niño-Southern Oscillation exerts a discernible influence on the seasonality of extreme precipitation. El Niño induces delayed extremes in the Huai and lower Yangtze River Basin, but earlier events in the Northwest and Pearl River Basin. Notable reduced SI during El Niño versus La Niña phases, indicating La Niña intensifies precipitation seasonality. This study plays a pivotal role in advancing our understanding of extreme precipitation events, ultimately promoting resilience and reducing vulnerabilities to weather-related disasters.

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