Abstract
The extreme floods in the Middle/Lower Yangtze River Valley (MLYRV) during June−July 2020 caused more than 170 billion Chinese Yuan direct economic losses. Here, we examine the key features related to this extreme event and explore relative contributions of SST anomalies in different tropical oceans. Our results reveal that the extreme floods over the MLYRV were tightly related to a strong anomalous anticyclone persisting over the western North Pacific, which brought tropical warm moisture northward that converged over the MLYRV. In addition, despite the absence of a strong El Niño in 2019/2020 winter, the mean SST anomaly in the tropical Indian Ocean during June−July 2020 reached its highest value over the last 40 years, and 43% (57%) of it is attributed to the multi-decadal warming trend (interannual variability). Based on the NUIST CFS1.0 model that successfully predicted the wet conditions over the MLYRV in summer 2020 initiated from 1 March 2020 (albeit the magnitude of the predicted precipitation was only about one-seventh of the observed), sensitivity experiment results suggest that the warm SST condition in the Indian Ocean played a dominant role in generating the extreme floods, compared to the contributions of SST anomalies in the Maritime Continent, central and eastern equatorial Pacific, and North Atlantic. Furthermore, both the multi-decadal warming trend and the interannual variability of the Indian Ocean SSTs had positive impacts on the extreme floods. Our results imply that the strong multi-decadal warming trend in the Indian Ocean needs to be taken into consideration for the prediction/projection of summer extreme floods over the MLYRV in the future.
摘要
2020 年 6-7 月份长江中下游地区发生的极端洪涝灾害给我国造成了 1700 多亿的直接经济损失. 本研究调查了与该极端降水事件相关的重要特征, 并探索了热带三大洋不同海盆海温对该极端事件的相对贡献. 研究发现此次长江中下游极端降水与较强的西北太平洋异常反气旋有关, 该反气旋将热带区域水汽向北输送并在长江中下游地区辐合. 另外, 尽管 2019 年冬季赤道太平洋没有发生较强的 El Niño 事件, 热带印度洋暖海温异常在 2020 年 6-7 月份达到了近 40 年来的最大值, 其中 43% (57%) 是由于年代际增暖 (年际变率) 导致的. NUIST CFS1.0 模式 (该模式能够在 3 月份较好地预报出长江中下游地区夏季降水增多现象) 的敏感性试验结果表明, 相比于海洋大陆、 赤道中东太平洋以及北大西洋区域的海温异常, 印度洋暖海温异常在此次长江中下游极端降水事件中起着主要作用, 并且印度洋海温的年代际增暖信号和年际变率信号均起着一定的作用. 我们的研究结果表明在预测未来长江中下游地区夏季极端降水时需要将印度洋海温的年代际增暖趋势考虑进去.
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Acknowledgements
This work is supported by National Natural Science Foundation of China (Grant No. 42030605 and 42088101) and National Key R&D Program of China (Grant No. 2020YFA0608004). The model simulation was conducted in the High Performance Computing Center of Nanjing University of Information Science & Technology. The OISST is downloaded from https://www.ncdc.noaa.gov/oisst/data-access website. CMAP precipitation data and NCEP-NCAR Reanalysis-1 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, are downloaded from the website at https://psl.noaa.gov/.
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Article Highlights
• The extreme floods over the MLYRV in June–July 2020 were tightly tied to a stronger-than-normal Subtropical High persisting over the western North Pacific, which brought abundant tropical warm moisture northward that converged over the MLYRV.
• Compared to SST anomalies in other tropical oceans, the record-breaking warm SST anomalies in the tropical Indian Ocean played a dominant role in generating the summer extreme floods in 2020 over the MLYRV.
• The rapid SST warming in the tropical Indian Ocean implies more frequent occurrence of the extreme summer floods over the MLYRV in the future, which requires special attention.
This paper is a contribution to the special issue on Summer 2020: Record Rainfall in Asia—Mechanisms, Predictability and Impacts.
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Tang, S., Luo, JJ., He, J. et al. Toward Understanding the Extreme Floods over Yangtze River Valley in June–July 2020: Role of Tropical Oceans. Adv. Atmos. Sci. 38, 2023–2039 (2021). https://doi.org/10.1007/s00376-021-1036-8
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DOI: https://doi.org/10.1007/s00376-021-1036-8