The transition to humid extreme cold events in winter during the past six decades over China

Winter extreme cold events (ECEs) pose significant economic and health risks, particularly when cold is combined with humidity. Although global warming has led to a decline in overall ECE occurrences, the changes in humid ECEs remain uncertain. This study uses dry and wet-bulb temperatures to categorize dry and humid ECEs across China and analyzes the proportion of humid ECEs, and the underlying factors influencing this phenomenon. In contrast to the decreasing trend of winter relative humidity (RH), our findings show an increase in RH during ECEs. This observation suggests a shift toward more humid conditions during these events. Further analysis shows an increasing percentage of humid ECEs, especially in Xinjiang, where the occurrence of dry ECEs is decreasing. Classifying ECEs into temperature- or humidity-dominated types reveals a significant increase in humidity-dominated humid ECEs, which is driven mainly by specific humidity changes, not temperature changes. These findings highlight the urgent need for adaptation strategies for more humid ECEs in a warming climate.