Pang et al. (2025) Comparison of the heatwaves of 2022 and 2024 in the Sichuan Basin, China: the similarity and different roles of oceans and BSISO

Identification

• Journal: Climate Dynamics
• Year: 2025
• Date: 2025-12-22
• Authors: Yishu Pang, Jie Wu, Boqi Liu, Changyan Zhou, Li Guo
• DOI: 10.1007/s00382-025-07997-x

Research Groups

• Sichuan Climate Center/Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province, Chengdu, China
• State Key Laboratory of Climate System Prediction and Risk Management/China Meteorological Administration Key Laboratory for Climate Prediction Studies, National Climate Centre, China Meteorological Administration, Beijing, China
• State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China

Short Summary

This study compares the mechanisms of the unprecedented 2022 and 2024 heatwaves in the Sichuan Basin, China, revealing common large-scale circulation patterns (European–East Asian teleconnection) but distinct oceanic forcings (Indo-Pacific Tripole/North Atlantic Tripole in 2022 vs. Tropical North Atlantic/North Atlantic Tripole in 2024) and the amplifying role of boreal summer intraseasonal oscillation stagnation.

Objective

• To compare the characteristics and underlying mechanisms of the unprecedented persistent–extensive heatwaves (PEHWs) in the Sichuan Basin (SCB) in 2022 and 2024.
• To elucidate the commonalities and disparities in their formation, particularly focusing on the roles of distinct sea surface temperature anomaly (SSTA) patterns and the boreal summer intraseasonal oscillation (BSISO).
• To understand why the 2024 PEHW peaked in September despite different climatic backgrounds compared to 2022.

Study Configuration

• Spatial Scale: Sichuan Basin (28° N–32.5° N, 103.5° E–110° E), China, and broader Eurasian/Indo-Pacific regions for teleconnections.
• Temporal Scale: Heatwave events in July–September (JAS) of 2022 and 2024. Data analysis period: 1981–2024 (SST-related calculations: 1982–2024). Anomalies defined relative to 1991–2020 climatology.

Methodology and Data

• Models used:
  • Thermodynamic equation for thermal budget analysis.
  • Wave activity flux (WAF) calculation (Takaya and Nakamura, 2001).
  • Empirical Orthogonal Function (EOF) decomposition.
  • Lanczos filter for timescale decomposition (synoptic, subseasonal, interannual, interdecadal components).
  • Multiple linear regression.
  • Composite analysis.
  • Student’s t-test for significance.
• Data sources:
  • Daily maximum air temperatures at 2-meter height (Tmax) from 2276 observational stations in China (National Meteorological Information Center of the China Meteorological Administration).
  • Hourly ERA-5 reanalysis dataset (1.0° × 1.0° horizontal resolution) for geopotential height, air temperature, horizontal wind, and vertical velocity.
  • Daily outgoing longwave radiation (OLR) data (2.5° × 2.5° horizontal resolution) from NOAA (1981–2022) and FY-3D satellite (2023–2024).
  • Global monthly-mean sea surface temperatures (SSTs) on a 1/4° × 1/4° grid from NOAA OI SST V2 High Resolution Dataset (1982–2024).

Main Results

• Heatwave Characteristics:
  • 2022 PEHW: Occurred in midsummer, with the most intense event lasting 32 days (28 July–28 August). Peak regional mean Tmax reached 41 °C, with 100% station coverage and heat intensity (HI) exceeding 40 °C.
  • 2024 PEHW: Delayed to August–September, with the most intense event from 19 August to 21 September. Peak regional mean Tmax exceeded 39 °C, with 99.2% station coverage and HI reaching 39.5 °C. September 2024 recorded an unprecedented Tmax anomaly of approximately +7 °C.
• Drivers of Tmax Anomalies: Both events were primarily driven by interannual (37.7% in 2022; 68.7% in 2024) and intraseasonal (37.4% in 2022; 29.7% in 2024; 30–90-day band) variability, after accounting for a global warming trend (21.95% in 2022; 17.5% in 2024).
• Common Circulation Background: The mid-tropospheric European–East Asian (EEA) teleconnection pattern, characterized by a "quasi-saddle" shape and a "cold vortex to the north, heat dome to the south" dipole over East Asia, served as the common circulation background. This led to an enhanced and westward-extended Western Pacific Subtropical High (WPSH) and South Asian High (SAH).
• Thermal Budget: Adiabatic heating from anomalous subsidence was the primary warming process for both PEHWs, with stronger adiabatic heating observed in 2024. In 2022, anomalous meridional heat advection from southeasterly wind anomalies provided additional warming.
• Interannual SSTA Forcing:
  • 2022: The EEA pattern was modulated by strong positive Indo-Pacific Tripole (IPT) and North Atlantic Tripole (NAT) SSTA modes (both exceeding +2 standard deviations). The IPT enhanced the Walker and Hadley Cells, intensifying the WPSH. The NAT triggered a positive North Atlantic Oscillation (NAO) and dispersed Rossby waves to East Asia.
  • 2024: The EEA pattern was driven by the synergistic forcing of strong positive NAT (> +2 standard deviations) and Tropical North Atlantic (TNA) SSTA modes (> +2 standard deviations). The TNA excited dual Rossby-wave trains, with southern waves intensifying the WPSH and northern waves propagating eastward along the westerlies. The Rossby-wave train and wave activity fluxes were stronger in 2024.
• Intraseasonal BSISO Role: 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 local meridional circulation and suppressing convection over China.
  • 2022: BSISO1–Lanczos index stagnated in Phase 5 for 13 active days (three times the climatological mean).
  • 2024: BSISO1 and BSISO1–Lanczos indexes persisted in Phases 5 and 6 for 21 out of 26 days (Phase 6 activity five times the climatological mean).
• Peak Period Determination: Divergent BSISO stagnation durations in Phases 5–6 primarily governed the distinct peak periods of the two PEHW events (midsummer in 2022 vs. September in 2024).
• Land-Atmosphere Feedback: Both events exhibited high land-atmosphere coupling, where decreased evaporation and enhanced sensible heating due to soil drying contributed to surface warming. The 2022 event showed higher coupling due to drier soil conditions.

Contributions

• Provides the first comparative analysis of the unprecedented 2022 and 2024 extreme heatwaves in the Sichuan Basin, identifying both shared and distinct formation mechanisms.
• Clarifies the specific roles of different oceanic SSTA patterns (IPT/NAT vs. TNA/NAT) in modulating the interannual variability of the European–East Asian teleconnection for these two events.
• Highlights the critical role of BSISO stagnation in specific phases (5–6) in amplifying heatwave intensity and determining their distinct peak timings, particularly explaining the unprecedented September peak in 2024.
• Deepens the understanding of multi-scale (interannual and subseasonal) drivers of extreme heatwaves, offering potential for improved prediction skill for such events in Southwestern China.

Funding

• National Key R&D Program of China (2024YFC3013100)
• Natural Science Foundation of Sichuan Province, China (2024NSFSC0066; 2025ZNSFSC1138)
• National Natural Science Foundation of China (41905067)
• Special Operating Expenses of Scientific Research Institutions for “Key Technology Development of Numerical Forecasting” of the Chinese Academy of Meteorological Sciences
• CMA Youth Innovation Team (CMA2024QN06)
• Key Innovation Team of Sichuan Meteorological Bureau (SCQXTD202402)
• Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province (SCQXKJYJXZD202404; SCQXFPZJ2025-04)
• Innovation and Development Program of China Meteorological Administration (CXFZ2025J033, CXFZ2023J002)
• China Meteorological Administration Key Laboratory for Climate Prediction Studies (CMA-LCPS-23-02)

Citation

@article{Pang2025Comparison,
  author = {Pang, Yishu and Wu, Jie and Liu, Boqi and Zhou, Changyan and Guo, Li},
  title = {Comparison of the heatwaves of 2022 and 2024 in the Sichuan Basin, China: the similarity and different roles of oceans and BSISO},
  journal = {Climate Dynamics},
  year = {2025},
  doi = {10.1007/s00382-025-07997-x},
  url = {https://doi.org/10.1007/s00382-025-07997-x}
}