Causes of desertification

Desertification is a natural (unnatural) phenomenon that the productivity of soil is reduced or lost in a large area due to drought, lack of rain, vegetation destruction, wind erosion, running water erosion, soil salinization and other factors. ?

There are narrow sense and broad sense, which originated in the late 1960s and early 1970s. The severe drought in the Sahara region of West Africa caused unprecedented disasters, and the word "desertification" began to spread.

The final result of desertification is mostly desertification, and China is one of the countries with serious desertification in the world. Desertification control needs extensive international cooperation and the participation of all countries in the world.

1, narrow sense

Desertification in a narrow sense is desertification. Under the sandy surface conditions in extremely arid, arid, semi-arid and semi-humid areas, due to the influence of natural factors or human activities, the balance of natural fragile ecosystems has been destroyed, and the land degradation process characterized by sandstorm activities has gradually formed wind erosion and aeolian landform landscape.

The key to the definition is "sandy surface conditions". Because of this, any land with desertification process is called desertification land. Desertification land also includes places where sand dunes move forward and invade under the action of wind, and sand dune activation areas where the original fixed and semi-fixed sand dunes produce quicksand activities due to vegetation destruction. ?

2. Universal

It refers to the total process of natural environment degradation (including salinization, grassland degradation, soil erosion, soil desertification, narrow sense desertification, vegetation desertification, sand dune intrusion in historical period and other specific natural environment degradation marked by certain environmental factors) in arid, semi-arid or even semi-humid areas.

Extended data:

I. Present situation of desertification

Dryland accounts for 40% of the world, of which 70% in Africa is desert and dryland. Although there are rainforests in Latin America and the Caribbean, 65,438+0/4 of its land is desertification or arid land. There are 400 million people living in desert or dry land in Asia, and the area of dry land is increasing by about 2500 square kilometers every year. Of course, dry land does not mean barren land. ?

Human activities such as production, life, war and agriculture have long influenced the process of natural desertification. Such as over-planting, leading to nutrient loss and soil erosion; Overgrazing beyond the carrying capacity leads to vegetation loss and soil erosion, which is difficult to recover.

About half of cattle,13 of sheep and 2/3 of goats in the world graze in arid areas. Overirrigation leads to water evaporation, while salt remains in the soil, and the formed salinized land also belongs to degraded land.

Irrigated cultivated land in the world accounts for 17% of the total cultivated land and contributes 40% to the world grain output. However, partly due to floods and salinization, crop yields have declined, resulting in the degradation of about 2 million hectares of land. ?

More seriously, desertification and poverty aggravate each other and form a vicious circle. In the short term, poverty will lead to more unreasonable use and development of land and natural resources. At the same time, desertification threatens food production, affects biodiversity, affects political stability, leads to migration, and causes and aggravates poverty.

The United Nations Environment Programme estimates that desertification directly affects the lives of 250 million people in more than 1 10 countries. Threatened arid land accounts for 40% of the land area, involving about 2 billion people, both developed and developing countries, such as southern Africa, the Middle East, southern Russia, Australia, the United States, Mexico, northern Brazil, western South America and even Iceland.

Desertification has affected 16% of global agricultural land, and 75% of agricultural land in Central America, 20% of agricultural land in Africa and 1 1% of agricultural land in Asia have been seriously degraded. Due to desertification, the annual crop loss in the world is estimated at 42 billion dollars, mainly in developing countries in Asia and Africa. China loses $6.5 billion annually due to desertification, and rural GDP in sub-Saharan Africa loses 3% due to desertification.

The International Committee of the Red Cross estimates that half of the refugees in the world are environmental refugees. Many Mexicans who immigrate to the United States illegally come from arid areas. 16 of Niger's population has moved because of desertification.

Two. Types of desertification

1, wind erosion

The area of wind erosion and desertification land in China is 6.5438+0.607 million square kilometers, mainly distributed in arid and semi-arid areas, which is the largest and most widely distributed among all kinds of desertification land.

Among them, the arid area is about 876 thousand square kilometers, which is generally distributed in the west of Langshan Mountain in Inner Mongolia. The Tengger Desert and the north of Longshou Mountain include the north of Hexi Corridor, the Qaidam Basin and its north, and the west of Tibet.

The semi-arid area is about 492,000 square kilometers, which is generally distributed in the east and south of Langshan Mountain in Inner Mongolia, passing through Hangjinhouqi, Chengkou County and Wuhai City, and then passing through the central and eastern Hexi Corridor to Subei Mongolian Autonomous County, showing a continuous large-scale distribution. The sub-humid arid area is about 239,000 square kilometers, mainly distributed in the east of the Mu Us Desert and the east of Inner Mongolia, east longitude 106 degrees.

2. Water erosion

The total area of water erosion and desertification in China is 205,000 square kilometers, accounting for 7.8% of the total area of desertified land. It is mainly distributed in the Wuding River, Kuye River and Tuwei River basins in the northern part of the Loess Plateau, and mainly distributed in the middle and upper reaches of Xiliao River and Daling River in the northeast.

3, freezing and thawing

The area of freeze-thaw desertification land in China is 366,000 square kilometers, accounting for 13.8% of the total area of desertification land. Freeze-thaw desertification land is mainly distributed in high altitude areas of Qinghai-Tibet Plateau.

4. Soil salinization

The total area of salinized land in China is 233,000 square kilometers, accounting for 8.9% of the total area of desertification. The areas where soil salinization is concentrated are Qaidam Basin, Oasis around Tarim Basin, piedmont alluvial plain at the northern foot of Tianshan Mountain, Hetao Plain, Yinchuan Plain, North China Plain and Yellow River Delta.

References:

Baidu encyclopedia-desertification