What is the disaster caused by the flood?

Rivers, oceans, lakes and other water bodies rise above a certain level, threatening the safety of related areas and even causing disasters. Also known as flood. In China, the word "flood" comes from the Yao Dian of Shangshu in the pre-Qin period. Since then, there have been many flood records in more than 4,000 years, and the earliest flood record in Europe is as far away as 1450 BC. The flood records of the Tigris-Euphrates River in West Asia and the Nile River in Africa can be traced back to the 40th century BC. Flood is a natural phenomenon and a natural disaster, which is caused by natural factors such as rainstorm, rapid melting of ice and snow, storm surge and so on. Objectively speaking, there are irresistible reasons for frequent floods, which can be said to be "destiny". However, why did the Yangtze River, which has been surging through the ages, never return in the short period of 100 in the 20th century? Why does the once-in-a-century flood turn into a disaster every few years? Once a decade?

Compared with relevant historical data, the frequency and severity of floods are quite consistent with the trend of population growth. We have to admit that the rapid population growth, the expansion of cultivated land, land reclamation around lakes, deforestation and other human activities in China constantly change the surface state, change the confluence conditions, and aggravate the degree of floods. Rainfall depends on the sky, and water diversion depends on people. In a rainy year, whether floods cause disasters and the magnitude of flood disasters are closely related to human factors. Long-term forest destruction is an important reason. The biggest mistake made by mankind is cutting down forests. As the main body of terrestrial ecosystem, forest has many functions, such as water conservation, soil and water conservation, climate regulation and so on, and plays an irreplaceable role in reducing flood peak. A flood is not necessarily a flood, but it destroys forests, and even a small flood can cause a big flood. The flood regulation function of forest is mainly as follows: 1. Forest canopy can intercept a part of heavy rain through its huge leaves, which can reach10 ~ 30%; 2. Its litter layer has the function of storing rainwater; 3. Because of the existence of forest, the infiltration capacity of the surface is greatly enhanced, and a large number of rapid surface runoff becomes slow underground runoff; 4. Forests can also change the surface structure of soil and enhance the ability to store precipitation; 5. The forest has a huge root system, which has the functions of consolidating soil and regulating the sediment injected by flood into rivers.