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Magnitude, Scale, and Dynamics of the 2020 Mei-yu Rains and Floods over China


Large parts of East and South Asia were affected by heavy precipitation and flooding during early summer 2020. This study provides both a statistical and dynamical characterization of rains and floods affecting the Yangtze River Basin (YRB). By aggregating daily and monthly precipitation over river basins across Asia, it is shown that the YRB is one of the areas that was particularly affected. June and July 2020 rainfall was higher than in the previous 20 years, and the YRB experienced anomalously high rainfall across most of its sub-basins. YRB discharge also attained levels not seen since 1998/1999. An automated method detecting the daily position of the East Asian Summer Monsoon Front (EASMF) is applied to show that the anomalously high YRB precipitation was associated with a halted northward progression of the EASMF and prolonged mei-yu conditions over the YRB lasting more than one month. Two 5-day heavy-precipitation episodes (12−16 June and 4−8 July 2020) are selected from this period for dynamical characterization, including Lagrangian trajectory analysis. Particular attention is devoted to the dynamics of the airstreams converging at the EASMF. Both episodes display heavy precipitation and convergence of monsoonal and subtropical air masses. However, clear differences are identified in the upper-level flow pattern, substantially affecting the balance of airmass advection towards the EASMF. This study contextualizes heavy precipitation in Asia in summer 2020 and showcases several analysis tools developed by the authors for the study of such events.


2020 年初夏, 东亚和南亚许多地区均受到暴雨和洪水的强烈影响. 本研究给出此次影响长江流域强降水和洪水的统计学和动力学特征. 通过对亚洲各大流域日降水和月降水资料的分析表明, 长江流域是受此次强降水影响最为明显的区域之一. 2020 年 6-7 月长江流域降水为过去20年间最强, 且强降水覆盖了流域内绝大多数地区. 长江流量为 1998/1999 年以来最大. 利用一种可以自动识别日尺度东亚夏季风锋的方法, 分析东亚夏季风锋与强降水之间的关系, 结果表明长江流域降水异常偏多与东亚夏季风锋北抬过程停滞、 长江流域上空持续超过一个月的梅雨环流背景相关. 选取两个持续 5 天的强降水过程 (2020 年 6 月 12-16 日和 7 月 4-8 日), 利用拉格朗日轨迹追踪法, 分析降水中动力过程, 重点关注与东亚夏季风锋期气流辐合相关的动力特征. 在两段降水过程中, 季风气流和副热带气流的辐合均与强降水相伴出现; 但高层环流型差异明显, 这极大影响了东亚夏季风锋附近水平平流的平衡. 本研究以 2020 年夏季亚洲强降水为例, 展示了作者发展的一系列分析方法在此类强降水事件中的应用方法和前景.


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AV, MM, RS, AGT and NPK were supported by the COSMIC project through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund, contract number P106301. NPK was supported by a Natural Environmental Research Council (NERC) Independent Research Fellowship (NE/L010976/1) and by the ACREW programme of the National Centre for Atmospheric Science. We thank Omar V. MÜLLER for help with GloFAS-ERA5.

Author information




RS: Abstract and Introduction; AV: Data and Methods, Section 4, and Conclusions; MM: Data and Methods, Section 3 and Conclusions; all: feedback on the manuscript. All authors contributed to the conception and design of the analysis, which was carried out by AV, MM and RS.

Corresponding author

Correspondence to Ambrogio Volonté.

Additional information

Article Highlights

• The YRB experienced its heaviest and most extreme June–July rainfall in the last 20 years.

• The Yangtze River discharge was the highest it has been since 1998/1999.

• The northward progression of the EASMF was halted, with prolonged mei-yu conditions over the YRB.

• Heavy rainfall events are associated with airmass convergence at the EASMF, controlled by the upper-level flow pattern.

This paper is a contribution to the special issue on Summer 2020: Record Rainfall in Asia—Mechanisms, Predictability and Impacts.

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Volonté, A., Muetzelfeldt, M., Schiemann, R. et al. Magnitude, Scale, and Dynamics of the 2020 Mei-yu Rains and Floods over China. Adv. Atmos. Sci. 38, 2082–2096 (2021).

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Key words

  • East Asian summer monsoon
  • 2020 China floods
  • Yangtze River basin
  • mei-yu front
  • extreme precipitation


  • 东亚夏季风
  • 2020 年中国洪水
  • 长江流域
  • 梅雨锋
  • 极端降水