Causes of land desertification

Land desertification simply means land degradation, also called "desertification". The 1992 United Nations Conference on Environment and Development defined the concept of desertification as follows: "Desertification is the occurrence of land degradation in arid, semi-arid and sub-humid areas with drought disasters due to factors such as climate change and irrational human economic activities. Degradation. On the second World Day to Combat Desertification and Drought on June 17, 1996, the Secretariat of the United Nations Convention to Combat Desertification issued a communiqué stating that the current phenomenon of desertification in the world is still intensifying, among which more than 1.2 billion people are directly threatened by desertification. 135 million people are in danger of losing their land in the short term. Desertification is no longer a simple ecological and environmental problem, but has evolved into an economic and social problem. As of 1996, it has brought poverty and social instability to mankind. The global desertified land has reached 36 million square kilometers, accounting for 1/4 of the entire earth's land area, which is equivalent to the combined land area of ??Russia, Canada, China and the United States. There are more than 100 countries affected by desertification in the world. People are fighting against desertification, but desertification is expanding at a rate of 50,000 to 70,000 square kilometers per year, an area equivalent to Ireland. By the end of the twentieth century, about one-third of the world's cultivated land will be lost. Among the environmental problems, desertification is one of the most serious disasters. For people threatened by desertification, desertification means that they will lose the most basic basis of survival-the disappearance of productive land.

Desertification in the narrow sense (i.e., desertification) refers to an environmental change process similar to desert landscapes in areas that were not originally deserts due to excessive human economic activities under fragile ecosystems. Any land that undergoes desertification processes is called desertified land. Desertified land also includes areas where sand dunes move forward due to wind force on the edge of the desert and areas where original fixed or semi-fixed dunes undergo sand dune activation due to vegetation destruction. < /p>

Desertification in the broad sense refers to the degradation of the natural environment in arid, semi-arid or even semi-humid areas due to the combined effects of man-made and natural factors (including salinization, grassland degradation, soil erosion, soil desertification, desertification in the narrow sense, The overall process of vegetation desertification, sand dune advance and invasion in historical periods and other specific natural environment degradation marked by a certain environmental factor)

From a global perspective, the United Nations Resolution on Environmental Protection in Environmental Protection adopted in 1994. Countries experiencing severe drought and/or desertification, especially in the African Convention to Combat Desertification, desertification refers to drought (arid), semi-arid (semi-arid) and subtropical regions caused by various factors including climate variability and human activities. Land degradation in dry subhumid areas

This definition clarifies three issues:

① "Desertification" is caused by various factors including climate variability and human activities. Originated and developed under the influence of factors;

② "Desertification" occurs in arid, semi-arid and subhumid arid areas (referring to the ratio of annual precipitation to potential evapotranspiration) between 0.05 and 0.65 (but excluding the polar and subpolar regions), which gives the background conditions and distribution range of desertification;

③ "Desertification" occurs in arid, semi-arid and subtropical regions. Land degradation in humid and arid zones places desertification within a broad global land degradation framework, thereby defining its regional scope.

In the late 1960s and early 1970s, successive years of severe drought in the Saharan region of western Africa caused unprecedented disasters and caused the international community to pay close attention to land degradation in dry areas around the world. The term "desertification" began to spread. According to the United Nations, one-fifth of the world's population and one-third of the world's land are currently affected by desertification. At the World Conference on Environment and Development in June 1992, the prevention and control of desertification was listed as a priority area for development and action by the international community. In 1993, the United Nations Convention to Combat Desertification in Countries Experiencing Serious Drought or Desertification (especially in Africa) was launched. 》intergovernmental negotiations. The text of the convention was officially adopted on June 17, 1994. In December 1994, the United Nations General Assembly passed a resolution to designate June 17 every year as the "Global Day to Combat Desertification and Drought" from 1995 to publicize it to the public. Our country is one of the parties to the Convention.

What is desertification? In the past, we often understood it as "the desert continues to expand, spreading the sand in the desert to an increasingly wider area of ??fertile land." This is inaccurate. The definition adopted at the World Conference on Environment and Development in 1992 is "land degradation in arid, semi-arid and sub-humid areas caused by various factors, including climate and human activities." That is, the decrease or loss of soil productivity caused by strong wind erosion, water erosion, soil salinization, etc. is called desertification.

my country's desertification situation is very serious. According to materials published by the State Forestry Administration's Desertification Prevention and Control Office and other government departments in 1998, my country is one of the countries with serious desertification in the world. According to the national desert, Gobi and sandified land census and desertification survey results, my country's desertified land area is 2.622 million square kilometers, accounting for 27.4% of the country's land area, and nearly 400 million people are affected by desertification. According to research from the China-U.S.-Canada International Cooperation Project, China's direct economic losses caused by desertification are approximately 54.1 billion yuan.

Among the desertified lands in my country, the area of ??wind-eroded desertification caused by strong winds is the largest, accounting for 1.607 million square kilometers. According to statistics, since the 1970s, the land desertification area has expanded at a rate of 2,460 square kilometers per year.

The desertification of the land creates a material source for the sand blown by strong winds. Therefore, sandstorms in northern my country (strong sandstorms are commonly known as "black winds" because it is often difficult to see when entering a sandstorm) are occurring more and more frequently, with high intensity and a wide range. On May 5, 1993, severe sandstorms occurred in Xinjiang, Gansu, and Ningxia, resulting in 116 people dead or missing, 264 injured, tens of thousands of livestock lost, 337,000 hectares of crops affected, and direct economic losses of 540 million yuan. From April 15 to 21, 1998, a severe sandstorm swept across my country's arid, semi-arid and sub-humid regions from west to east, passing through Xinjiang, Gansu, Ningxia, Shaanxi, Inner Mongolia, Hebei and western Shanxi. On April 16, dust floating in the sky settled in Beijing, Tianjin and the area north of the lower reaches of the Yangtze River, forming a large area of ??floating dust weather. Among them, in Beijing, Jinan and other places, "mud rain" fell from the sky due to the encounter between floating dust and rainfall clouds. Due to the continuous rain of sand in Yinchuan, Ningxia, planes were grounded and people found it difficult to breathe.

According to records, from the 3rd century BC to 1949, there were 70 recorded severe sandstorms in northwest my country, occurring once every 31 years on average. This has happened 71 times in the past 50 years since the founding of the People's Republic of China. Although there are large differences in standards between historical records and current meteorological observations, there is no problem in proving that sandstorms are much more common now than in the past.

Based on the analysis of land satellite image data of 17 typical sandy areas in my country at the same location in different periods, it also proves that the development situation of desertification in my country is very serious. Mu Us Sandy Land is located at the junction of Inner Mongolia, Shaanxi and Ningxia, covering an area of ??approximately 40,000 square kilometers. In the past 40 years, the area of ??quicksand has increased by 47%, the area of ??forestland has decreased by 76.4%, and the area of ??grassland has decreased by 17%. Due to overgrazing and firewood cutting in the southern part of the Hunshandake Sandy Land, the area of ??shifting sand increased by 98.3% in just 9 years, while the area of ??grassland decreased by 28.6%. In addition, the shrinkage of the Minqin oasis in Gansu, the demise of the Populus euphratica and tamarisk forests in the lower reaches of the Tarim River in Xinjiang, the degradation of pastures and the disappearance of the Haloxylon ammodendron forest in the Alxa region of Gansu... a series of grim facts have sounded the alarm to us.

The final result of land desertification is mostly desertification.

Types and distribution of desertification in my country

There are four types of desertified land in my country: wind erosion desertification, water erosion desertification, freeze-thaw desertification, and soil-inlaid salinization.

The area of ??wind-eroded desertified land in my country is 1.607 million square kilometers, mainly distributed in arid and semi-arid areas. It is the largest and most widely distributed among various types of desertified land.

kind. Among them, there are about 876,000 square kilometers of arid areas, generally distributed west of Langshan Mountain in Inner Mongolia, north of Tengger Desert and Longshou Mountain, including the north of Hexi Corridor, Qaidam Basin and its north , west to

northern Tibet. The semi-arid area is about 492,000 square kilometers, generally distributed from the east to the south of Langshan in Inner Mongolia, passing through Hangjinhou Banner, Chengkou County, Wuhai City, and then westward through the central part of the Hexi Corridor. It is distributed in a continuous large area from the east to Subei Mongolian Autonomous County.

The subhumid and arid area is about 239,000 square kilometers, mainly distributed from the east of the Mu Us Desert to the right east of Inner Mongolia and 106 degrees east longitude.

The total area of ??water-eroded desertification in my country is 205,000 square kilometers, accounting for 7.8% of the total desertified land area. It is mainly distributed in the Wuding River, Kuye River, Tuwei River and other river basins in the northern part of the Loess Plateau. In the northeastern region, it is mainly distributed in the middle and upper reaches of the Xiliao River and the Daling River

of the upstream.

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

The total area of ??salinized land in my country is 233,000 square kilometers, accounting for 8.9% of the total desertification area. Comparison of soil salinization

The areas with concentrated and contiguous distribution include the Qaidam Basin, the oases around the Tarim Basin, the piedmont alluvial plains at the northern foot of the Tianshan Mountains, the Hetao Plain, and the Yinchuan Plain , North China Plain and Yellow River Delta.