How did the flash floods break out?

The topographic features of mountain torrents and debris flows are generally middle and high mountains, with large relative height difference and steep valley slopes. The surface layer is covered with thick soil, and the bottom of the soil is broken rock cut by medium-deep faults and their derived faults.

forest coverage rate

Large areas of forests and bamboo are covered. During the flood season, when warm and humid air carries a large amount of water vapor over the forest area, it meets the cold air with low temperature and high relative humidity in the forest area, which is easy to cause local heavy precipitation.

Water source conditions

Water is not only a component of mountain torrents and mudslides, but also a stimulating factor, mainly from rainfall. To stimulate mountain torrents, first, the previous rainfall and a continuous rainfall work together. Second, the previous rainfall and the maximum rainfall 1 hour play a leading role in stimulating. The water content of the soil on the top of the mountain is saturated, and the water pressure in the rock cracks below the soil increases sharply. In case of heavy rain, energy accumulates rapidly; As a result, the balance of the original soil was destroyed, and the pressure water in the rock and soil cracks broke through the surface overburden and instantly poured down from the middle and upper parts of the mountain, forming mountain torrents and mudslides.

When the warm and humid airflow is blocked by the mountain, the warm and humid airflow moves upward, forming cold and warm fronts at the top of the mountain and windward slopes, resulting in thunderstorms. The ground is still very hot because the upper part of the mountain extends into the clouds. When the rain came, the middle and upper part of the mountain was already two stories. So it often rains for a short time on the ground. Flash floods broke out.

The cause of mountain torrents is not only mountain structure, but also short-term thunderstorm caused by trumpet-shaped estuary topography.