Diversity and Formation Characteristics of Persistent Wet–Cold Compound Extreme Events in China

Despite global warming, persistent wet–cold compound extreme events (PWCEs) during wintertime still occurred frequently in China, causing significant disruption to human and social activities. However, their full range, precursors, and evolution characteristics remain unclear. In this study, we have objectively identified 252 PWCEs in China during cold seasons from 1961 to 2023 and further classified them into the South China (SC), Western China (WC), and Central China (CC) types. Although the frequency of PWCEs decreased under global warming, they still exhibit strong extremity, and the WC-type events even show an upward trend in their intensity. The three types of PWCE events share a similar ”north-high–south-low” meridional pattern over mid-high latitude but demonstrate significantly different circulation evolution characteristics and precursors: the SC type is dominantly driven by cold-air outbreak linked to the Baikal blocking-East Asian trough; the WC type is controlled by the zonal wave train along the South-Asian subtropical westerly jet; the CC type is embedded within a well-organized mid-latitude great-circle wave train across Eurasia. Their associated moisture transports also show diverse pathways: the SC type primarily harvests moisture from the South China Sea, the WC-type from the India-Burma trough, and the CC type from both the Northwest Pacific anticyclone and the South China Sea. The precursors for PWCEs are mainly originated from the Madden-Julian Oscillation by modulating the tropical circulation and moisture transports, especially for the WC and CC types. These findings highlight the diverse formation characteristics and precursors underlying PWCEs in China, offering valuable insights for improving subseasonal predictions of compound extreme events.