Regarding the problem of floods in various places, what are the causes of flash floods?

Humans are doing things like they are doing (emitting exhaust gases into the sky, destroying the ozone layer, etc.) and worsening the climate, and the rain is not adjustable.

A flash flood is a flood that occurs in a mountain stream or ravine.

Mountain floods are generally divided into torrential rain mountain floods, snowmelt mountain floods, glacial flash floods, etc.; It is sudden, the water volume is concentrated, the flow rate is large, the erosion is destructive, and the water flow carries sediment and even stones, which often causes local floods.

Reasons for the formation of flash floods: the terrain of flash flood disaster-prone areas is often high, steep, deep valleys, large cutting depths, erosion valleys are developed, and most of its geology is soil with little permeability intensity, such as argillaceous rock, slate shale developed into weak erosion resistance soil, easy to soften and disintegrate when exposed to water, which is very conducive to the rapid collection of surface runoff after heavy rainfall, and when encountering a strong surface runoff impact, thus forming flash flood disasters.

Flash floods briefly explain the causes of the occurrence of the world:

1. Topographic conditions:

Generally, the topographic characteristics of flash floods and debris flows are medium and high mountainous areas, with large relative elevation differences and steep river valley slopes. The surface layer is covered with thick soil with grafting, and the bottom layer of the soil is a broken rock layer cut by medium-deep faults and their derivative faults.

2. Forest cover conditions:

When the warm and humid air carries a large amount of water vapor in the flood season, it reaches the air above the forest area, and the cold air with low temperature and high relative humidity in the forest area is easy to cause large local precipitation.

3. Water source conditions:

Water bodies are both components and triggers of flash floods and debris flows, mainly from rainfall.

1. Crop yields were reduced by disasters. Major floods have caused a large amount of farmland to be washed away and submerged, crop yields have been reduced or even lost, and the agricultural product processing industry and light industry have lacked raw materials or the cost of raw materials has increased, resulting in factory production reduction and shutdown, followed by unemployment of workers.

2. The interruption of transportation and communication makes the information and transportation blocked or delayed, resulting in a large number of product backlogs and deterioration, insufficient raw materials, and a decline in production capacity. In particular, the blockage of emergency relief supplies is likely to amplify existing disasters.

3. Major flood disasters have caused a decline in the living standards of the people in the disaster areas, and there is a lack of basic livelihood guarantees, resulting in a large number of victims, disrupting the normal social order and impacting all aspects of society.

4. Cause great damage to the environment on which human beings depend. For example, floods will cause soil erosion every year, a large amount of soil and its nutrients are lost, resulting in poor land, and at the same time, the sediment content in the water flow increases, resulting in the attenuation of river function, the shrinkage of lakes, and the desertification of cultivated land, and the serious consequences are incalculable.

5. The pollution of the water environment by flooding mainly includes the spread and spread of toxic and harmful substances such as germs, parasites, industrial waste residues, waste liquids, chemical fertilizers, pesticides, etc., which will seriously endanger people's lives and health. In addition, flooding will have a significant impact on shipping, transportation, tourism, aquaculture, etc.

There are three main factors for the occurrence of flash floods: 1) Geological and geomorphological factors. The topography of the flash flood disaster-prone areas is often high mountains, steep slopes, deep valleys, large cutting depths, erosion valleys, and most of its geology is soil with little permeability intensity, such as purple sand shale, argillaceous rock, red sandstone, and slate shale to develop weak erosion resistance soil, which is easy to soften and disintegrate when exposed to water, which is very conducive to the rapid collection of surface runoff after heavy rainfall, and when it encounters a strong surface impact, it forms a flash flood disaster.

2) Meteorological and hydrological factors. The northward and southward movement of the subtropical high, the southward invasion and northward retreat of the westerly circulation, and the convergence and convergence of the southeast monsoon and the southwest monsoon have formed an unstable climate system in mountainous areas, often resulting in continuous or concentrated high-intensity rainfall. Rising temperatures lead to faster melting of snow and ice or flooding due to the failure of flood containment projects. According to statistics, the occurrence of flash floods is mainly due to the continuous excessive rainfall in the affected areas in the early stage, which saturates the soil water and loosens the surface.

From the physical process of overall occurrence and development, it can be seen that the occurrence of flash floods is mainly caused by continuous rainfall and short-term heavy rainfall.

3) Human activity factors. Flash floods are prone to occur in hilly areas due to over-exploitation of land, or steep slope reclamation, or engineering construction that causes damage to the mountain, changes the topography and landform, destroys natural vegetation, cuts down forests indiscriminately, and loses the role of water conservation. Due to the continuous encroachment of the river channel caused by human activities, the river channel is seriously silted up, and the flood discharge capacity of the river channel is reduced, which is also one of the important factors for the formation of flash flood disasters.