1in the summer of 1998, a serious flood occurred in the Yangtze River in China, causing serious disasters. What is the main cause of this disaster?

1. The occurrence of El Ni? o phenomenon leads to abnormal climate and increased precipitation.

2. Excessive deforestation in the middle and upper reaches of the Yangtze River has led to a decline in water conservation capacity in the upper reaches.

3. Long-term reclamation around lakes in the Yangtze River basin has led to the decrease of lake wetland area and the decline of storage capacity in the main stream of the Yangtze River.

The Yangtze River valley is densely populated, and many people live in low-lying areas regardless of danger.

5. The Yangtze River basin lacks permanent flood discharge area.

6. At that time, the Three Gorges Dam had not been built, and the ability of manpower to regulate flood peaks was insufficient.

7. In recent years, the sediment content in the Yangtze River has increased, and the rivers have silted up and the drainage is not smooth.