From low to high, urban flood control early warning levels are divided into four early warning levels: general, heavy, serious and especially serious, which are represented by blue, yellow, orange and red respectively.
Flood is a natural phenomenon caused by natural factors such as rainstorm, rapid melting of ice and snow, storm surge and so on.
As the main body of terrestrial ecosystem, forest has many functions, such as water conservation, soil and water conservation, climate regulation and so on. A flood does not necessarily have a flood, but destroys the forest. A small flood can also cause a big flood. Therefore, it is very important to protect the forest. Wanton deforestation is not only harmful to themselves, but also to future generations. Many parts of the world, such as Mesopotamia, Asia Minor and the southern slope of the Alps, have finally become barren due to excessive deforestation. （FangHongDengJiFenWeiJiGeDengJi）