Causes of frequent natural disasters

The reasons for frequent natural disasters are:

① The destruction of vegetation and overgrazing have caused grassland degradation and desertification, and the land desertification is serious, which poses a serious threat to agricultural production and human life.

(2) The sharp decline of forests, unreasonable utilization of forest resources, cutting the superior and leaving the inferior, and deforestation have led to the decline of forest ecosystem.

(3) Over-reclamation has seriously degraded the land, the per capita forest area has decreased year by year, and the soil water storage capacity has weakened, leading to an increase in sandstorms and serious soil erosion. Overexploitation and unreasonable production and lifestyle have destroyed the ecological balance and caused serious environmental deterioration.

Species extinction is a natural process, but at present, human activities have greatly accelerated the speed of species extinction. Once a species is extinct, it cannot be regenerated.

⑤ Population expansion and social growth have a great impact on resources, environment and social development, and the increasing population has put great pressure on social economy.

Classification of natural disasters

Natural disasters are divided into eight categories: meteorological disasters, marine disasters, floods, geological disasters, earthquake disasters, crop biological disasters, forest biological disasters and forest fires.

Meteorological disaster

There are more than 20 kinds of meteorological disasters, mainly including the following types:

(1) rainstorm: mountain torrents, river flooding and urban water accumulation;

(2) Rain and waterlogging: waterlogging;

(3) Drought: drought in agriculture, forestry and grassland, water shortage in industry, cities and rural areas, and land desertification;

(4) Dry-hot wind: dry-hot wind and foehn wind;

(5) High temperature heat wave: extreme heat and high temperature, human diseases, burns, and crop ripening;

(6) Tropical cyclones: gale, rainstorm and flood;

(7) Cold damage: crops, livestock and fruit trees are harmed by strong cooling and low temperature;

(8) Freezing injury: frost, crop and livestock freezing injury, water pipes and oil pipes freezing injury;

(9) Freezing rain: wires, branches and roads are frozen;

(10) Freezing: rivers, lakes and seas freeze, and roads freeze after rain and snow;

(1 1) Snow damage: snowstorm, snow;

(12) Hail disaster: destroying crops and houses;

(13) Wind disaster: falling trees, reversing houses, reversing cars and reversing boats;

(14) Tornado: local destructive disaster;

(15) Lightning: lightning casualties;

(16) dense fog: human diseases and traffic jams;

(17) low-altitude windshear: aviation accident;

(18) Sandstorm: human and animal deaths, building collapse, agricultural production reduction, air pollution and topsoil loss.

Marine disasters

(1) Storm surge: The interaction between cold air from high latitudes and tropical cyclones from the sea leads to the occurrence of coastal strong winds and huge waves one after another, thus forming a storm surge. The western Pacific is the area that produces the most storm surges.

Storm surge type: typhoon type; Cold high pressure combined with cyclone type in the Yellow Sea and Bohai Sea; Transverse cold and high pressure type; Strongly isolated yellow sea and Bohai sea cyclone type; Strong Mongolian low pressure type.

Spatial distribution of storm surge disasters. Storm surges in China are all over the coast, but the main concentrated areas from north to south are: Laizhou Bay; Jiangsu Xiaoyanghekou to Zhejiang Dehaimen; Wenzhou, Taizhou, Shacheng to Minjiang Estuary; Shantou, Guangdong to the Pearl River Estuary; The east coast of Leizhou Peninsula and the northeast coast of Hainan Island.

(2)? Catastrophic waves: The waves that cause disasters at sea are called catastrophic waves.

Formation of disastrous waves: caused by typhoon, temperate cyclone, cold wave and other weather systems and formed by strong winds.

According to the type of weather system, disastrous waves are cold and high pressure (also called cold wave type); Typhoon type; Cyclone type; Cold high pressure combined with cyclone.

(3) Sea ice: Sea ice is frozen by harmful water, including river ice and icebergs flowing into the ocean. Sea ice is one of the outstanding marine disasters in polar oceans and some high latitudes.

Disaster caused by sea ice. Pushing down offshore oil platforms, destroying offshore engineering facilities and waterway facilities, or colliding with ships, causing major shipwrecks; Obstruct the navigation of the ship, damage the propeller or hull, and lose navigation ability. Sea ice blocks the harbor, which leads to the normal operation of the port or greatly increases the cost of using icebreakers to break ice and pilot; The fishing moratorium is too long, and mariculture facilities and places are destroyed, resulting in economic losses.

The main characteristics of sea ice disasters are the Bohai Sea, the northern Yellow Sea and the coastal waters of Liaodong Peninsula, as well as some bays of Shandong Peninsula, which are easy to freeze in winter in China.

(4)? Tsunami: Tsunamis are mainly marine disasters caused by violent earthquakes in countries along the Pacific Ocean.

Conditions for tsunami formation: the focal point of the submarine earthquake that caused the tsunami is shallow, generally less than 20 km to 50 km; The magnitude is generally above 6.5 on the Richter scale; There must be a large-scale vertical movement on the seabed; The sea area where submarine earthquakes occur must have a certain depth, especially the transoceanic tsunami, which is generally above 1000 meters.

Hazards of Tsunami: The form of tsunami in coastal areas is the sharp rise of seawater, which suddenly forms a "water wall" marching towards the shore, accompanied by rumbling noise, and instantly invades coastal land, engulfing fertile fields and villages and towns, and then the seawater suddenly recedes, or rises first and retreats, and sometimes appears repeatedly, causing huge losses to human life and property.

(5)? Red tide: the concept of red tide: Red tide is the phenomenon that seawater changes color for a certain period of time due to the sudden increase of some tiny phytoplankton, protozoa or bacteria in seawater under certain environmental conditions.

Harm of red tide: causing marine variation, partially interrupting the marine food chain and threatening the survival of marine life; Some red tide organisms excrete or decompose mucus after death, which makes marine animals filter food and breathe, thus suffocating them. Or the toxins contained in red tide organisms are ingested by marine animals, resulting in poisoning and death of fish, shrimp and shellfish. Some will poison vertebrates and humans after eating. In the following sections, we will introduce several common natural disasters with large destruction areas, and also introduce some disaster prevention and relief measures.

(6) El Nino phenomenon: refers to the abnormal continuous warming of seawater temperature in the tropical ocean in the eastern and central Pacific Ocean, which changes the global climate pattern, causing drought in some areas and excessive rainfall in some areas.

Flood damage

(1) rainstorm disaster;

(2) mountain torrents;

(3) snowmelt flood;

(4) ice flood;

(5) dam-break flood;

(6) Debris flow and cement flood.

geologic hazard

Both natural variation and human activities may lead to changes in geological environment or geological body. When this change reaches a certain level, landslides, debris flows, land subsidence, ground collapse, rock swelling, sand liquefaction, land freezing and thawing, soil salinization, land desertification, earthquakes, volcanoes, geothermal disasters and other consequences will do harm to human beings and society. This phenomenon is called geological disaster. Geological disasters also include derivative disasters.

(1) Debris flow: Debris flow is a special torrent containing a lot of sediment and stones, which is triggered by heavy rain, melting of snow and ice and other water sources in mountain valleys.

The formation of debris flow: the following three conditions must be met at the same time: steep terrain is convenient for water collection and water collection; Abundant loose matter; There is a lot of water in a short time.

The material composition of debris flow can be divided into three categories: debris flow consists of a large number of cohesive soil, sand particles and stones with different particle sizes; Mainly cohesive soil, containing a small amount of clay particles and stones, with high viscosity, which is called mud flow when it becomes thick mud; Water-rock flow consists of water, sand and stones of different sizes.

Hazard of debris flow: hazard to residential areas; Harm to roads and railways; Harm to water conservancy and hydropower projects; Damage to mines;

(2)? Landslide: the phenomenon that the rocky mountain on the landslide slides down along a weak surface (or weak zone) due to various reasons, which is called landslide. Commonly known as "walking mountains", "crossing mountains" and "sliding soil".

Conditions of landslide: Only when the rock and soil mass of the slope is cut and separated into a continuous state by various structural planes can it have the conditions of downward sliding.

The activity intensity of landslide is mainly related to the scale, speed, distance, accumulated potential energy and generated kinetic energy of landslide.

Activity time of landslide: it is mainly related to various external factors that induce landslide, such as earthquake, rainfall, freezing and thawing, tsunami, storm surge and human activities.

(3)? Collapse: Collapse, also known as caving, collapse or collapse, is a geological phenomenon in which the rock mass on the steep slope suddenly breaks away from the parent body under the action of gravity and accumulates at the toe of the slope (or gully rock).

According to the material composition of collapse, collapse can be divided into two categories: soil collapse and rock collapse.

Activity time of collapse: collapse generally occurs during or after heavy rain and long-term continuous rainfall; In the fierce process; During or after the excavation of slope toe; The initial stage of reservoir impoundment and the peak period of rivers; After strong mechanical vibration and big blasting.

Regionality of collapse: Southwest China is the main area of collapse distribution in China.

(4) Land subsidence: Land subsidence is the crustal deformation caused by long-term drought, which lowers the groundwater level and over-exploits groundwater.

(5) Earthquake: Earthquake is a devastating natural disaster. Earthquakes not only directly cause landslides, ground fissures and house collapses, but also cause secondary disasters such as fires, floods, explosions, landslides, mudslides, the spread of toxic gases and plagues.

earthquake disaster

(1) tectonic earthquake;

(2) Collapse earthquake;

(3) mine earthquake;

(4) Reservoir earthquake, etc.

Crop biology

(1) Crop diseases: mainly including more than 240 kinds of rice diseases, more than 50 kinds of wheat diseases, more than 40 kinds of corn diseases, more than 40 kinds of cotton diseases and many diseases such as soybean, peanut and hemp;

(2) crop pests; There are mainly 252 kinds of rice pests, more than 0/00 kinds of water wheat pests, 52 kinds of corn pests, more than 300 kinds of cotton pests and many other crop pests.

(3) Crop weeds: about 8,000 species;

(4) Rat damage.

Forest life

(1) Forest diseases: 29 18 species;

(2) Forest pests: 5020 species;

(3) Forest rodents: 160 species.

In addition to earthquakes, floods, typhoons, plagues and other disasters that seriously affect our lives and even threaten our lives, we should constantly raise our awareness and strengthen our ability to prevent other disasters such as lightning, fog and hail.