Spatiotemporal Evolution of Winter Extreme Low Temperature Days in China and Their Causality

Amid global warming, China's winter extreme low temperature events exert increasingly significant impacts on energy/power systems, agriculture, and public health. Understanding their spatiotemporal evolution and driving mechanisms remains a key climate research focus.This study utilizes the CN05.1 dataset (daily minimum temperature interpolated from >2,400 stations) to define winter Extreme Low Temperature Days (ELDs) using a percentile-based threshold (19612020). Analysis incorporates reanalysis data (NCEP/NCAR, HadISST) including sea level pressure, geopotential height, and wind fields.Results reveal a significant warming trend in winter minimum temperatures across China from 19612020, with a regional mean increase exceeding 3C. Correspondingly, winter ELDs declined markedly, with a >50% reduction in the regional average occurrence.A key interdecadal shift occurred around 1985, particularly evident in northern China. Empirical Orthogonal Function (EOF) analysis identified two dominant ELD spatial modes: EOF1 (48.63% variance): Shows a nationally coherent decline in ELDs with strong interdecadal characteristics around 1985. EOF2 (13.89% variance): Displays a northsouth dipole pattern characterized by interannual fluctuations.Correlation analysis links EOF1 to: the southward shift of the Arctic vortex, a weakened Siberian High, and warm SST anomalies in the equatorial Pacific. EOF2 appears to be associated with different circulation features. These include intensified polar vortex activity, Ural blocking highs, and an eastwest SST dipole pattern in the tropical Pacific.