Impacts of changing atmospheric circulations and declining spring Barents Sea ice on more frequent summer heatwave in Southern China

In Southern China (SC), heatwaves have intensified and became more frequent since the early 2000s. Using Self- Organizing Maps (SOM), SC heatwaves were classified into four distinct types. SOM1, the dominant pattern (accounting for 75.9 % events), centered in the Yangtze River Basin. The most severe events in this category featured a maximum temperature (Tmax) of 44.5 degrees C, impacted 600 stations, and lasted for 13 days. SOM1 was primarily influenced by the westward extension of the Western Pacific Subtropical High (WPSH), the eastward extension of the South Asian High (SAH), abnormal European Blocking (EB) and Silk Road Pattern (SRP). Four most extreme heatwaves were categorized under SOM2, including the 2022 mega heatwave, which recorded a higher T max (45.0 degrees C), broader coverage (623 stations), and longer duration (36 days). These events are driven by much stronger EB, WPSH, and SAH anomalies, indicating a more intensified circulation pattern compared to SOM1. SOM3 comprising eight events, primarily affected eastern SC. In contrast, SOM4 including two cases mainly affected western SC. Increased SC heatwaves have been linked to changing large-scale circulations and spring Barents Sea ice loss. Random Forest quantified the relative importance of different large-scale circulation factors, revealing that the reconstructed circulation pattern associated with SOM1 showed a significant enhancement, with its contribution to heatwaves increasing from 14.5 % to 47.2 % since the early 2000s. Spring Barents Sea ice loss influenced SC heatwaves by adjusting aforementioned circulations, especially after the early 2000s, supported by diagnosis and numerical experiments.