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<p>The Middle-Lower Yangtze River Basin (MLYRB) typically experiences above-normal precipitation in the summer following a strong El&#xa0;Niño, making El&#xa0;Niño a key indicator for flood season predictions. However, persistent heavy rainfall events (PHREs) have also occurred under weak El&#xa0;Niño conditions in recent decades, with unclear mechanisms posing forecasting challenges. Using a spatiotemporal continuity method, this study analyzes two representative PHREs under strong and weak El&#xa0;Niño backgrounds to compare their rainfall distribution, circulation, moisture transport, low-level jets, vorticity, and K&#xa0;index, aiming to reveal the dynamic mechanisms of PHREs during weak El&#xa0;Niño conditions. Results show that: (1) The 2016 event featured a southwest–northeast rain belt that moved northeastward and weakened, with higher total rainfall, larger extent, and stronger peak intensity than the 2020 event. Conversely, the 2020 event exhibited an east–west rain belt that shifted eastward, moved southward, and weakened. (2) Both events were influenced by the Western Pacific Subtropical High (WPSH) and the southwest jet, but their dominant mechanisms differed: the 2016 event, driven by a strong El&#xa0;Niño, featured an intensified WPSH that enhanced large-scale moisture transport, whereas the 2020 event was mainly governed by mesoscale convective systems, with the low-level jet and moisture convergence promoting local convection. (3) The 2020 event received additional moisture from the Eurasian continent and had a deeper, more unstable warm–moist layer. Overall, the 2016 event featured abundant moisture but weaker convection, whereas the 2020 event had less moisture but stronger convection, highlighting differences in the formation of PHREs. We suggest that under weak El&#xa0;Niño conditions, greater attention should be paid to mesoscale convection and local instability.</p>

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Comparative dynamics of two persistent heavy rainfall events in the middle-lower Yangtze river basin under strong versus weak El Niño

  • 期刊论文

  • 发表日期：

    2026年3月3日

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  • Dan Wu,
  • Yu Liu,
  • Li-Ying Ning,
  • Yu-Xuan Wu,
  • Yong-Ping Wu,
  • Guo-Lin Feng,
  • Tao Su

摘要

The Middle-Lower Yangtze River Basin (MLYRB) typically experiences above-normal precipitation in the summer following a strong El Niño, making El Niño a key indicator for flood season predictions. However, persistent heavy rainfall events (PHREs) have also occurred under weak El Niño conditions in recent decades, with unclear mechanisms posing forecasting challenges. Using a spatiotemporal continuity method, this study analyzes two representative PHREs under strong and weak El Niño backgrounds to compare their rainfall distribution, circulation, moisture transport, low-level jets, vorticity, and K index, aiming to reveal the dynamic mechanisms of PHREs during weak El Niño conditions. Results show that: (1) The 2016 event featured a southwest–northeast rain belt that moved northeastward and weakened, with higher total rainfall, larger extent, and stronger peak intensity than the 2020 event. Conversely, the 2020 event exhibited an east–west rain belt that shifted eastward, moved southward, and weakened. (2) Both events were influenced by the Western Pacific Subtropical High (WPSH) and the southwest jet, but their dominant mechanisms differed: the 2016 event, driven by a strong El Niño, featured an intensified WPSH that enhanced large-scale moisture transport, whereas the 2020 event was mainly governed by mesoscale convective systems, with the low-level jet and moisture convergence promoting local convection. (3) The 2020 event received additional moisture from the Eurasian continent and had a deeper, more unstable warm–moist layer. Overall, the 2016 event featured abundant moisture but weaker convection, whereas the 2020 event had less moisture but stronger convection, highlighting differences in the formation of PHREs. We suggest that under weak El Niño conditions, greater attention should be paid to mesoscale convection and local instability.