**1. Introduction**

The Yangtze River valley has observed several heavy rainfall and flooding events in the last century [1], which caused large casualties and economic losses. Extreme precipitation events are the primary causes of flooding disasters [2–5]. Understanding the characteristics of past extreme precipitation events—including the temporal and spatial distribution characteristics of precipitation anomalies and the formation mechanism—is important for future flood control and disaster reduction [6,7].

Effected by the geographical location, the factors causing precipitation anomalies in the Yangtze River valley are very intricate and including the intra-seasonal oscillation of West Pacific subtropical high cyclones over East Asia, cross-equatorial wind anomalies, the Asian polar vortex, Asian meridional circulation, as well as sea surface temperature(SST) anomalies due to ENSO(El Niño-Southern Oscillation) [8–10]. As the strongest interannual change signal of ocean–atmosphere interaction, the evolution of ENSO events largely affects the precipitation over the Yangtze River valley in China [11–13]. The abnormal convective activities over the Philippines caused by the SST anomalies provoke anticyclones at the bottom of the troposphere in the region [14]. Such circulation with anticyclonic anomalies tends to continue into the following summer, consequently causing anomalies regarding

**Citation:** Cai, J.; Zhang, S.; Zhang, Y.; Li, M.; Wei, Y.; Xie, P. Characteristics and Cause Analysis of the 1954 Yangtze Precipitation Anomalies. *Remote Sens.* **2022**, *14*, 555. https:// doi.org/10.3390/rs14030555

Academic Editor: Kenji Nakamura

Received: 28 October 2021 Accepted: 20 January 2022 Published: 24 January 2022

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the location, intensity, and seasonal movements (north- and southbound) of the West Pacific subtropical high (WPSH) [15,16], affecting the East Asian monsoon, and resulting in increased rainfall in the Yangtze River valley. As the generation of ENSO is relatively slow, and the observation mode indicated by SST anomalies is intuitive, an ENSO event can be an important basis for predicting summer precipitation. In fact, the current prediction system in China depends—to a great extent—on the prediction of an ENSO signal [17,18], and it has achieved primary success in the prediction of summer precipitation in China [19]. Consequently, the analysis of historical precipitation anomalies related to SST anomalies in the Yangtze River valley is of great significance for reliable projections of future extreme precipitation events in this region.

In the summer of 1954, the most severe flood of the past century occurred in the Yangtze River valley. At the time, the flood level hit a historic high of 29.73 m at the Hankou weather station, with a peak discharge of 76,100 m3/s [20]. A solid conclusion regarding the mechanism of 1954's heavy rain has not been reached.

Some research focused on the causes of this flood has been conducted. Feng et al., (2004) explored the superposition of multiple physical factors that were observed during the 1954 Yangtze floods [21], and proposed that the ENSO event in 1953 is an important factor causing the flood. Chen (1957) analyzed the atmospheric circulation (AC) features at the Yangtze River valley during the flood season in 1954 [22], indicating that the formation of the Okhotsk high and a cold trough above the Tibetan Plateau were closely related to the unusual precipitation over the drainage basin that year. Some studies demonstrated that AC anomalies are strongly correlated to SST anomalies, and that SST anomalies occur before AC anomalies [11–13], directly causing unusual precipitations. Lu Jiong (1954) proposed that the Pacific SST anomalies played a crucial role in summertime precipitation anomalies across China [23]. These studies indicate that the precipitation anomalies over the Yangtze River valley in 1954 should be closely related to the Pacific SST anomalies.

Previous studies on the 1954 flood were limited by the number of stations and data quality [22,24]. However, the current mass of data provides an opportunity for retrospective research. The China Meteorological Data Service Centre recently published high-quality surface climate and daily observation data [25]. In the construction of ground-basic meteorological data carried out by the China Meteorological Administration, the quality of the original data has been repeatedly checked and tested, bad data have been corrected, and missing data have been supplemented, which has significantly improved data quality. The National Weather Service of the United States also provided the global SSTs and geopotential data.

This study started with the spatiotemporal distribution characteristics of precipitation anomalies in 1954 over the Yangtze River valley. We explored the process of how the Pacific SST anomalies affected the circulation anomalies, and then induced the 1954 Yangtze precipitation anomalies. Based on the results of the analysis, we proposed a causal model relating the precipitation anomalies to the Pacific SST anomalies and the circulation anomalies, which can be used as a forecast tool for future severe flood disasters in the Yangtze River valley.
