Abstract:Based on observations from 2374 meteorological stations in China and the NCEP/NCAR reanalysis dataset, the spatio-temporal characteristics and causes of climate anomalies over China during autumn 2025 are analyzed. It was generally warmer than normal across China in autumn 2025, with the northern region of China exhibiting an intraseasonal “warm-cold-warm” temperature variation and the southern region showing a “warm in the early stage and cold in the late stage” pattern. The national average precipitation was the most since 1961 for the same period, with an uneven spatio and temporal distribution. In the early autumn, large-scale excessive precipitation with prominent extremeness occurred in southern North China, northern East China, northern Central China, and eastern Northwest China, finally leading to serious autumn flood. The autumn rain in West China started early, ended late and had a long duration, with the precipitation amount ranking the top in history. The formation of autumn flood in northern China was closely correlated to East Asian atmospheric circulation anomalies. The abnormally strong western Pacific subtropical high (WPSH) with an extremely northward ridge line, coupled with a robust low-level anticyclone over the Yellow Sea, provided favorable water vapor transport conditions, serving as the basic circulation background for the autumn flood in northern China. Additionally, the extreme meridional stability of the WPSH (i.e., little north-south movement) was another key circulation feature contributing to the flood. Furthermore, during the autumn, the equatorial central-eastern Pacific was in a developmental stage from cold water conditions to La Nia, accompanied by an extreme negative phase of the tropical Indian Ocean dipole (TIOD). The two factors, through pathways such as atmospheric teleconnections and local meridional-zonal circulation coupling, worked synergistically in influencing the anomalous configuration of the East Asian circulation, forming as an important oceanic external forcing background for the autumn flood in northern China in 2025.