A study suggests that warming in the Indian Ocean led to the extreme monsoon rainfall and flooding of the Yangtze River in 2020. Increased summer monsoon rain along the Yangtze River basin is typically linked to strong El Niño conditions. In 2020, however, deadly flooding followed a weak El Niño winter. Zhen-Qiang Zhou and colleagues report that warming in the Indian Ocean led to the extreme monsoon rains. To uncover possible predictors of the anomalous rainfall, the authors evaluated sea surface temperature effects using a global atmospheric model and observed monthly data from January 2019 to July 2020. The model predicted the excessive rainfall, with most of the effect attributable to temperature anomalies in the Indian Ocean rather than the Pacific Ocean. Next, the authors examined what may have contributed to the sea surface temperature anomalies, focusing on the 2019 Indian Ocean Dipole event, in which the temperatures of the eastern and western areas of the ocean differed more strongly than usual. The authors found that this positive dipole event, combined with the weak El Niño, excited Rossby waves in the Indian Ocean. The slowly propagating planetary waves deepened the thermocline by 70 m, increasing the penetration of warm surface water and contributing to sustained ocean warming. According to the authors, dynamic models incorporating global ocean events could help predict future summer monsoon dynamics.
Article #20-22255: "Historic Yangtze flooding of 2020 tied to extreme Indian Ocean conditions," by Zhen-Qiang Zhou, Shang-Ping Xie, and Renhe Zhang
MEDIA CONTACT: Shang-Ping Xie, Scripps Institution of Oceanography, La Jolla, CA; tel: 858-822-0053; email: email@example.com
Proceedings of the National Academy of Sciences