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<p>Eastern China experiences substantial rainfall variability, primarily driven by the East Asian summer monsoon system, characterized by the stepwise northward progression of the rainfall belt. The movement of the rainfall belt necessitates accurate forecasting to mitigate the risks associated with extreme weather events. Using Season-reliant Empirical Orthogonal Function (S-EOF) analysis, this study identifies a dominant seasonal rainfall mode, characterized by maximum rainfall over South China (SC) during spring (April–May) that shifts to the middle–lower Yangtze River basin (MLYZB) in summer (June–July). Composite analyses demonstrate that enhanced spring rainfall in SC is linked to intensified moisture transport associated with an anomalous western North Pacific anticyclone (WNPAC). By summer, the anomalous WNPAC shifts northwestward and strengthens, reinforcing south-westerly moisture flux into the MLYZB. Additionally, an expanded South Asian High (SAH) and a shallow monsoon trough over the South China Sea collectively establish a circulation pattern that benefits increased summer rainfall over the MLYZB. Idealized model experiments suggest that springtime diabatic heating from enhanced rainfall in SC can reinforce the WNPAC, pre-conditioning the circulation that favors subsequent summer rainfall in MLYZB. Lead-lag correlations further reveal a canonical El Niño-Southern Oscillation (ENSO)–Indian Ocean Dipole (IOD) sequence preceding this rainfall mode. After ENSO and IOD decay in winter, persistent basin-wide warming in the Indian Ocean helps sustain the anomalous WNPAC through summer, further influencing the monsoon circulation. By clarifying this coherent seasonal rainfall evolution and associated mechanisms, this study provides a physical basis for improved seasonal rainfall forecasts and hydrometeorological risk assessment.</p>

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Linkage and associated mechanisms between spring rainfall in South China and summer rainfall over the Yangtze basin revealed by the dominant seasonal evolution mode

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Ruoyu Ma,
  • Yue Zhang,
  • Xin Wang,
  • Wen Zhou

摘要

Eastern China experiences substantial rainfall variability, primarily driven by the East Asian summer monsoon system, characterized by the stepwise northward progression of the rainfall belt. The movement of the rainfall belt necessitates accurate forecasting to mitigate the risks associated with extreme weather events. Using Season-reliant Empirical Orthogonal Function (S-EOF) analysis, this study identifies a dominant seasonal rainfall mode, characterized by maximum rainfall over South China (SC) during spring (April–May) that shifts to the middle–lower Yangtze River basin (MLYZB) in summer (June–July). Composite analyses demonstrate that enhanced spring rainfall in SC is linked to intensified moisture transport associated with an anomalous western North Pacific anticyclone (WNPAC). By summer, the anomalous WNPAC shifts northwestward and strengthens, reinforcing south-westerly moisture flux into the MLYZB. Additionally, an expanded South Asian High (SAH) and a shallow monsoon trough over the South China Sea collectively establish a circulation pattern that benefits increased summer rainfall over the MLYZB. Idealized model experiments suggest that springtime diabatic heating from enhanced rainfall in SC can reinforce the WNPAC, pre-conditioning the circulation that favors subsequent summer rainfall in MLYZB. Lead-lag correlations further reveal a canonical El Niño-Southern Oscillation (ENSO)–Indian Ocean Dipole (IOD) sequence preceding this rainfall mode. After ENSO and IOD decay in winter, persistent basin-wide warming in the Indian Ocean helps sustain the anomalous WNPAC through summer, further influencing the monsoon circulation. By clarifying this coherent seasonal rainfall evolution and associated mechanisms, this study provides a physical basis for improved seasonal rainfall forecasts and hydrometeorological risk assessment.