The catastrophic flooding on the Yangtze River nearly 100 years ago was the result of El Niño’s influence combined with various other weather factors.
The City Hall of Hankou during the flood in 1931. (Photo: Sci Tech Daily).
The 1931 flood on the Yangtze River (also known as the Changjiang River) affected 25 million people and resulted in approximately 2 million fatalities. Recent studies link this disaster to both tropical and extratropical factors, while the lack of flood control measures exacerbated the impacts.
In the summer of 1931, an unprecedented disaster unfolded along the Yangtze River basin in eastern China. This was one of the deadliest natural disasters in history. The flooding inundated 180,000 square kilometers of land. Despite the severe social ramifications, the origins of the flood remain largely unexplored. This has posed a challenge due to the scarcity of historical records and meteorological data in China prior to the 1950s. However, access to important historical databases has recently enabled researchers to delve into the 1931 flood, as reported by Sci Tech Daily on September 10.
A study recently published in the journal Climate investigates the realities and mechanisms behind the great flood on the Yangtze River. The researchers found that the flooding resulted from the cumulative impact of sea surface temperatures associated with El Niño and wave activity across Eurasia. According to the research team, the flooding may have been intensified by heavy rainfall in the early spring of that year.
Led by Professor Tianjun Zhou from the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences, the team conducted analyses based on observations from instruments, reanalyzed databases, and simulated with a model of atmospheric circulation driven by sea surface temperatures. They observed that the flood in 1931 along the Yangtze River valley was influenced by rainfall in July. The total rainfall in July 1931 was not only the second highest in the previous decade, but it also exceeded many other periods from 1951 to 2000 in terms of persistence, according to Yueqi Zhou, a PhD candidate at IAP.
The researchers discovered that the prolonged heavy rainfall in July 1931 was associated with a Western Pacific Subtropical High (WPSH). The unusually warm sea surface temperatures in the Indian Ocean following the El Niño event caused the WPSH to extend southwestward. Simultaneously, the jet stream shifted southward due to extratropical wave activity, hindering the WPSH from moving northward in July as it typically would. All these factors enabled the WPSH to energize the rainband along the Yangtze River, leading to the devastating flood.
In their study, the scientists also examined flood control measures and disaster recovery. They concluded that the lack of preventive, responsive, and adaptive measures also contributed to the consequences.
