I wrote a short summary of the flood's ecological effects here.

With the Japanese pressuring the river crossing at Zhengzhou, the Guomindang First War Zone commanders believed the Chinese front was close to collapse in June 1938. If Zhengzhou fell, Japanese forces could then march along the Long-Hai railway (which ran along the south bank of the Yellow River) straight towards the temporary capital of Wuhan. Even more disastrously, the GMD troops retreating along the highway after the Xuzhou campaign of 1938 would be cut off. The combination of surrendering Wuhan and losing China's main fighting force (600,000 GMD troops had been committed to the Xuzhou campaign) would have effectively spelt the end of the GMD-led resistance. Under these circumstances, Chiang Kai-shek and GMD high command took the fateful decision to breach the dikes from 4 June to 9 June 1938.

This did give some breathing space to the GMD, though probably not as much as they would have liked. The units of the Japanese North China Area Army turned back from Zhengzhou and headed south, linking up with the forces near Nanjing. A few weeks after the flooding, a new Japanese push towards Wuhan was conducted upriver from Nanjing. Leapfrogging static Chinese positions through amphibious landings, Japanese forces advanced steadily and took Wuhan in October 1938. The breaching of the Yellow River dikes was an enormous man-made ecological disaster - however, the GMD considered it necessary for the survival of the nation. Xiong Xian-yu, the officer who oversaw the breaking of the dike, wrote in his diary:

This action has been taken to impede the enemy and to redeem the overall situation. For this reason, [we] did not hesitate to make this great sacrifice in pursuit of final victory.

Diana Lary's 'Drowned Earth: The Strategic Breaching of the Yellow River Dyke, 1938' (full reference in the linked answer) is a quick read that focuses on human suffering after the breaching; Muscolino's The Ecology of War in China: Henan Province, the Yellow River, and Beyond, 1938–1950 is a monograph that covers not only the breaching itself, but also how the GMD, Japanese and Communists interacted with the breached river throughout the Sino-Japanese War and the Chinese Civil War. The Ecology of War has great analysis and is certainly required reading on this subject, but it has been critiqued for its detached viewpoint and overuse of environmental jargon: the term for human activity in the book is, somewhat coldly, 'kinetic energy'.