How is the flood formed?

Water is one of the most useful resources on earth. We drink water, bathe, wash clothes and cook every day. Most of the time, water is very gentle and friendly. However, if the amount of water is large enough, the same substances we use to rinse our mouths and brush our teeth will overturn cars, destroy houses and even cause casualties. In the past hundred years alone, floods have claimed millions of lives, more than any other weather phenomenon. The formation of flood is due to the phenomenon that the water flow of rivers, lakes and oceans increases or the water level rises sharply due to heavy rain, snow melting, ice melting and dam break of reservoirs. When the flood exceeds a certain limit, it brings losses and disasters to human normal life and production activities, which is referred to as flood disaster for short.

Floods are prone to occur in rainy season. After the rain falls to the ground, part of it seeps into the ground; Some evaporate into the air; Some of them flow along the ground, pass through small ditches and streams, and enter rivers. The amount of water flowing into the river depends on the rainfall first. The heavier the rain, the more concentrated the time, and the more water will flow into the river. If a large amount of water flows into the river in a short time, if the water volume exceeds the maximum transport capacity of the river, floods will occur and cause floods. In addition, the formation of floods is also influenced by natural factors such as local climate, underlying surface and human activities.

1987 In July, Bangladesh experienced the biggest flood in history. The sudden natural disasters caused by heavy rains and strong winds in the past few days have left unprepared residents at a loss. In just two months, 47 of Bangladesh's 64 counties were hit by floods and rainstorms, resulting in more than 2,000 deaths, 25,000 livestock drowned, more than 2 million tons of grain destroyed, 20,000 kilometers of roads and 772 bridges and culverts washed away, tens of millions of houses collapsed, a large number of crops were damaged, and the number of people affected reached 20 million.

1In August, 975, in a rainstorm caused by a typhoon, two large reservoirs, Banqiao and Shimantan in Zhumadian, Henan Province, two medium-sized reservoirs, Zhugou and Tiangang, and 58 small reservoirs, broke their dams one after another in just a few hours. The rolling flood razed the village to the ground, the fertile land scraped three feet, the trees were uprooted, and the rails were twisted into twists. In this disaster named "July 8" flood, 29 counties and cities in Henan Province170,000 mu of farmland were flooded, of which 1 1 10,000 mu of farmland was affected. 5.96 million houses collapsed and 302,300 livestock and 720,000 pigs were washed away. The Beijing-Guangzhou line running through the north and south of China was washed away 102 km, stopped for 18 days, affected transportation for 48 days, and caused direct economic losses of nearly 10 billion yuan. Become the biggest reservoir dam-break tragedy in the world!

Floods always occur in places with dense population, high degree of agricultural reclamation, concentrated rivers and lakes and abundant rainfall. Floods often threaten the lives and property of people in rivers, lakes and offshore areas, and even cause floods. Since ancient times, floods have brought many disasters to mankind, and we can never stop them. It is an inevitable factor in the complex climate system of our atmosphere.