1938 Yellow River flood

The 1938 Yellow River flood (Chinese: 花园口决堤事件; pinyin: huāyuán kǒu juédī shìjiàn, literally "Huayuankou embankment breach event") was a flood created by the Nationalist Government in central China during the early stage of the Second Sino-Japanese War in an attempt to halt the rapid advance of Japanese forces. It has been called the "largest act of environmental warfare in history."

Following the onset of the Second Sino-Japanese War in 1937, the Imperial Japanese Army marched rapidly into the heart of Chinese territory. By June 1938, the Japanese had control of all of North China. On June 6, they captured Kaifeng, the capital of Henan, and threatened to take over Zhengzhou, the junction of the arterial Pinghan and Longhai Railways. Japanese success here would have directly endangered the major cities of Wuhan and Xi'an.

To stop further Japanese advances into western and southern China, Chiang Kai-shek, at the suggestion of Chen Guofu, determined to open up the dikes on the Yellow River near Zhengzhou. The original plan was to destroy the dike at Zhaokou, but due to difficulties at that location, the dike at Huayuankou, on the south bank, was destroyed on June 5 and June 7, with waters flooding into Henan, Anhui, and Jiangsu. The floods covered and destroyed thousands of square kilometers of farmland and shifted the mouth of the Yellow River hundreds of miles to the south. Thousands of villages were inundated or destroyed and several million villagers driven from their homes and made refugees. An official Kuomintang post-war commission estimated that 800,000 drowned, which may be an underestimate.

...
Wikipedia