On this day in 1931, the Yangtze River in China peaks during a horrible flood that kills 3.7 million people directly and indirectly over the next several months. This was perhaps the worst natural disaster of the 20th century.

The Yangtze River runs through southern China, one of the most populated areas on Earth. The region's people, most of whom lived at subsistence level, depended on the river for water for their personal and farming needs. In April, the river-basin area received far-above-average rainfall. When torrential rains came again in July, the stage was set for disaster. The Yangtze flooded over a 500-square-mile area. The rising waters drove 500,000 people from their homes by the beginning of August.

As the waters continued to rise in the first half of August and even more rain fell, the rice fields that dominated the landscape were swamped, destroying the crop. Major cities such as Wuhan and Nanjing depended on this rice and, without it, people in the cities starved to death. In addition, typhoid and dysentery were rampant due to the polluted river. The millions who died from this flood perished from starvation and disease, many after the flood waters had receded.

Much of the disaster may have been averted if flood-control measures had been followed closely. The Yangtze carries large amounts of sediment, which accumulates in certain areas of the river and must be cleared regularly. However, with much of the area's resources devoted to civil war at the time, the river was neglected.