Illustrate rain-related phenomena such as plum rain, acid rain and debris flow with examples. Talk about the causes of their formation and the disasters they bring to mankind. Urgent! ! !

Meiyu is a long-lasting rainy weather, which often occurs in early summer. It is mainly distributed in the Jianghuai Valley of China, passing through the southern tip of the Korean Peninsula to southern Japan and other places. From the middle and late June to the first half of July every year. Because plum rains occurred in the mature period of plums in southern China, people in China call this weather "plum rains", and this period is also called "plum rains season". In the rainy season, the air humidity is high and the temperature is high, so clothes are easy to get moldy, so some people call the rainy season "moldy rain". After the rainy season, the weather in Central China, South China, Taiwan Province Province and other places began to be dominated by the Pacific subtropical high, and officially entered the hot summer on the east coast of the mainland. Summer is controlled by the west side of subtropical high. The sinking air was originally dry, but it absorbed a lot of water vapor from the warm and humid sea surface, which brought abundant precipitation and produced a subtropical humid climate. Due to the strong contrast between land and sea, a unique monsoon climate has been formed here, characterized by rainy summer and dry winter, with rainfall concentrated in summer. Meiyu-causes disease. Disease 1: Diarrhea and wet weather, the stomach is prone to "accidents". Disease 2: Gynecological diseases. It is necessary to do gynecological examination in summer. Disease 3: Joint pain and dampness give rheumatism an opportunity. Sickness 4: Don't let your mood "mold" together. Disease 5: Dermatosis It rains on sunny days.

Acid rain is a by-product of high industrial development. Due to the extensive use of fossil fuels such as coal, oil and natural gas, sulfur oxides or nitrogen oxides produced after combustion have complex chemical reactions in the atmosphere, forming sulfuric acid or nitric acid aerosols, or being captured and absorbed by clouds, rain, snow and fog, and falling to the ground to become acid rain. If there is no cloud and rain when the acid substance is formed, the acid substance will gradually fall to the ground in the form of gravity sedimentation, which is called dry sedimentation, which is different from wet sedimentation such as acid rain and acid snow. When dry sediment meets water on the ground, it will recombine into acid.

Due to the increase of cloud cover, sunshine hours and solar radiation in urban areas decrease. As a result of the increase of smog particles in cities, the atmospheric transparency becomes worse, and smog greatly weakens the ultraviolet part of the sun (it can even be reduced by 30%-50% when the sun is low), which is also unfavorable to the health of urban residents. Acid rain can lead to soil acidification.

After soil acidification, it can accelerate the weathering of primary and secondary minerals containing aluminum in the soil, release a large number of aluminum ions and form aluminum compounds that can be absorbed by plants. Long-term excessive absorption of aluminum by plants will lead to poisoning and even death. Acid rain will also accelerate the loss of soil minerals and nutrients; Changing soil structure leads to poor soil and affects the normal development of plants; Acid rain can also induce plant diseases and insect pests and reduce crop yield. 4. Acid rain can dissolve hardened cement on the surface of nonmetallic building materials (concrete, mortar and lime-sand brick), produce cavities and cracks, reduce strength and damage buildings. Building materials become dirty and black, which affects the appearance and landscape quality of the city.

The harm of acid rain is various, including direct and potential harm to human health, ecosystem and building facilities. Acid rain will reduce children's immune function, increase the incidence of chronic pharyngitis and bronchial asthma, and increase the prevalence of eyes and respiratory tract in the elderly. Acid rain will also greatly reduce the yield of crops, especially wheat. Under the influence of acid rain, the yield can be reduced by 13% to 34%. Soybeans and vegetables are also susceptible to acid rain, which leads to the decrease of protein content and yield. Acid rain is also harmful to forests and other plants. It often turns the leaves of forests and other plants yellow, aggravates pests and diseases, and eventually causes large-scale death.

Acid rain is very harmful to forest plants. According to the domestic simulation experiment on the influence of 105 woody plants, when the pH value of precipitation is less than 3.0, it can cause direct damage to plant leaves, making them turn green and yellow and begin to fall off. The longer the leaves are exposed to acid rain, the more serious the damage. Field investigation shows that in areas where the PH value of precipitation is less than 4.5, a large number of yellow leaves fall off in Pinus massoniana forest, Pinus armandii forest and Abies fir forest, and the trees decline and die in pieces. The economic losses caused by acid rain to forest destruction are extremely huge.

Topographic and geomorphological conditions

Topographically, the mountain is high and the ditch is deep, the terrain is steep, the longitudinal drop of the ditch bed is large, and the shape of the flow city is convenient for water flow collection. Geomorphology, debris flow landforms can generally be divided into three parts: formation area, circulation area and accumulation area. The topography of the upstream formation area is mostly surrounded by mountains on three sides, and the water outlet on one side is spoon-shaped or funnel-shaped. The terrain is relatively open, the surrounding mountains are steep, the mountains are broken and the vegetation grows poorly. This terrain is conducive to the accumulation of water and debris. The topography of the circulation area in the middle reaches is mostly narrow and steep canyons, and the longitudinal slope at the bottom of the valley drops greatly, so that the debris flow can flow quickly and directly; The downstream accumulation area is an open and flat piedmont plain or valley terrace, which makes the accumulation place.

Source conditions of loose materials

Debris flow often occurs in areas with complex geological structure, developed faults and folds, strong neotectonic activity and high earthquake intensity. The development of adverse geological phenomena such as surface rock breakage, collapse, strewn at random and landslide provides a rich source of solid materials for the formation of debris flow.

Various debris flow pictures (10). In addition, areas with loose rock structure, weak rock structure, easy weathering, developed joints or soft and hard stratification can also provide rich debris sources for debris flows due to their fragility. Some human engineering activities, such as deforestation, mountain mining, quarrying and slag abandonment, often provide a large number of material sources for debris flows.

Water source conditions

Water is not only an important part of debris flow, but also the excitation condition and transport medium (power source) of debris flow. The water sources of debris flow include rainstorm, snowmelt water and reservoir water bursting. The main water sources of debris flow in China are heavy rain and long-term continuous rainfall, which is harmful to residential areas.

One of the most common hazards of debris flow is rushing into villages and towns, destroying houses, factories, enterprises and institutions and other places and facilities. Flooding people and animals, destroying land, and even causing disasters such as village destruction and death.

2. Harm to roads and railways

Debris flow can directly bury stations, railways, highways, destroy subgrade, bridges and other facilities, cause traffic disruption, and also cause subversion of running trains and cars, resulting in heavy casualties. Sometimes, debris flows into rivers, causing great changes in rivers, indirectly destroying buildings such as roads and railways, and even forcing roads to change lanes, causing huge economic losses.

3. Harm to water conservancy and hydropower projects

It is mainly used to wash away hydropower stations, water diversion channels, bridges across ditches, dams and other buildings, bury drainage ditches of hydropower stations, deposit reservoirs and abrade dam surfaces.

4. Harm to mines

It is mainly to destroy the mine and its facilities, bury the mine roadway, hurt the mine personnel, and cause the production to stop or even scrap the mine.