Comparison of the heatwaves of 2022 and 2024 in the Sichuan Basin, China: the similarity and different roles of oceans and BSISO

Unprecedented persistent–extensive heatwave (PEHW) events struck the Sichuan Basin (SCB) consecutively in July–September of both 2022 and 2024, posing serious threats to public health, energy supply, and ecosystems. These two PEHW events shared similar key circulation patterns but happened under distinct sea surface temperature (SST) backgrounds and peaked in different periods. This study investigates the underlying mechanisms responsible for the 2022 and 2024 PEHW events to elucidate their key commonalities and disparities. The mid-tropospheric European–East Asian teleconnection (EEA) pattern, dominated by interannual variability, is the common key circulation background of both events, leading to the westward extension of an enhanced Western Pacific Subtropical High. Correspondingly, adiabatic heating from enhanced descent dominates the thermal budget, with stronger adiabatic warming exhibited in the PEHW in 2024 and an anomalous southeasterly wind in 2022 providing additional meridional heat advection. However, in 2022, EEA variability was modulated by the combined influence of the Indo-Pacific Tripole and North Atlantic Tripole (NAT) SSTA modes; while in 2024, it was driven by the synergistic forcing of the NAT and Tropical North Atlantic modes, triggering Atlantic-sourced Rossby-wave energy that propagated downstream to East Asia. Superimposed on the background SSTAs, the stagnation of the boreal summer intraseasonal oscillation (BSISO) 1 in Phases 5–6 induced persistent convective anomalies over the Indochina Peninsula and South China Sea, enhancing both PEHW events by stimulating the local meridional circulation. Divergent BSISO stagnation durations in Phases 5–6 primarily govern the distinct peak period of the two PEHW events. The key factors on both interannual and subseasonal timescales uncovered by our results may contribute to improved understanding and prediction of extreme HWs in the SCB.