Specifically, the following paper can be prepared to tell you the truth.
The formation of desertification in China is the result of both natural and human factors. The natural aspect is mainly affected by climate change, and the human aspect mainly includes land reclamation, overgrazing, unreasonable excavation and cutting of Chinese herbal medicines and trees, and unreasonable use of water resources.
(1) Climate change
Relevant research shows that the most prominent feature of global climate change in the past century is the significant increase in temperature.
/kloc-from the end of 0/9 to the 1990s, the global average temperature rose by about 0.6℃, and the warming rate was 0.5℃/ 100 years. The temperature changes in China in the last hundred years are basically similar to the world average. According to the research, the lowest temperature in northern China increased significantly from1951-kloc-0/999, and warm winter years appeared continuously, with an obvious drought trend in recent 50 ~ 100 years. The drought trend began to accelerate in the 1970s.
Northwest China, where desertification land is concentrated, is located in the hinterland of the mainland, which is the region with the least precipitation, the largest evaporation and the driest in the same latitude in the world. The climate is getting warmer and the precipitation is decreasing, which aggravates the drought of climate and soil in this area. This makes the vegetation coverage in this area decrease, the soil structure becomes looser and the land desertification accelerates. In addition, climate warming and persistent drought in a large area have a serious impact on various water resources (glaciers, lakes, rivers, etc.). ), leading to glacier retreat, rivers reduced or cut off, lakes shrunk or dried up, and groundwater level dropped. Vegetation died in a large area due to lack of water, which lost the function of protecting the surface soil, accelerated the expansion of sandy land on both sides of the river and the activities of sand dunes on the edge of the desert, and made the desertification area expand continuously.
(2) Reclamation
In the western region where desertification is relatively concentrated, a large number of grasslands and woodlands have been reclaimed as cultivated land. From 1995 to 2000, the cultivated land area increased by grassland reclamation accounted for 69.5%, and the cultivated land area increased by woodland reclamation accounted for 22.4%. Because this area belongs to arid and semi-arid area, after grassland and woodland are reclaimed as cultivated land, the soil loses the protection of vegetation in the slack season, and the technical and socio-economic conditions are limited, which leads to the continuous expansion of cultivated land desertification area.
(3) Overgrazing
At present, the phenomenon of overloading and overgrazing in northwest China is becoming more and more serious, and the overloading rates in Xinjiang, Guangxi, Ningxia and Inner Mongolia are higher, reaching 12 1%, 8 1%, 72% and 66% respectively. Take Inner Mongolia Autonomous Region as an example, the grassland area owned by each sheep has decreased from 3.3 hectares in the 1950s to 0.87 hectares in the 1980s, and now it is only 0.42 hectares. Overgrazing has caused excessive trampling on the grassland surface, and the soil structure on the grassland surface has been seriously damaged. After wind erosion, a large number of wind erosion gaps appeared. The more grasslands grazing by livestock, the more exposed soil and the larger desertification area.
(four) unreasonable excavation and felling of Chinese herbal medicine trees.
In recent years, in the northwest region where the ecological environment is relatively fragile, large-scale indiscriminate excavation of wild Chinese herbal medicines such as Nostoc flagelliforme, hay and ephedra has occurred from time to time. According to the investigation conducted by Nature Protection Department of State Environmental Protection Bureau1June 1997165438+1October to1March 1997, in recent years, 200,000 farmers have entered Inner Mongolia every year. Since June 1987, the number of people who have entered Inner Mongolia has reached 1.9 million. The grassland covered by the "Cuofacai" army covers an area of about 220 million mu, covering five league cities including Xilin Gol League and Wulanchabu League in central and western Inner Mongolia. The grassland area of1.900 million mu has been seriously damaged, accounting for about 1.8% of the total grassland area in Inner Mongolia, and a considerable part of it is in the process of desertification. About 60 million mu of grassland area has been completely destroyed and has been desertified. Because 65.438+0.9 billion mu of grassland has been seriously damaged, it is impossible to graze, while other grasslands are forced to graze more than 65.438+0.9 billion mu, which is too heavy for grassland and accelerates the spread of desertification.
Unreasonable felling of trees leads to the sharp decrease of trees, which is another important reason for land desertification and frequent sandstorms in some areas. For example, in the early 1950s, there were 3.54 million mu of natural vegetation in Dunhuang in Hexi region, including 2 1.6 million mu of shrubs and 0/0.35 million mu of grassland. This 3.54 million mu green barrier is a very important shelter forest system directly facing the wasteland of Kumtag and Lop Nur on the periphery of Dunhuang Oasis. However, since the end of 1950s, there has been predatory utilization from near to far in Dunhuang, from cutting branches on the ground to digging roots underground, destroying 2 million mu of natural forests, and the vegetation died due to the drop of groundwater level. By 1980, the remaining area of natural forest is only 390,000 mu. The original sand-fixing vegetation in Qaidam Basin of Qinghai Province is more than 30 million mu. By the mid-1980s, due to deforestation, vegetation was destroyed and more than 1/3 of the land was desertified. Since 1970s, local residents in Jilantai Town, Inner Mongolia have cut down/kloc-0.05 million mu of natural forest in the northwest of Salt Lake to about 300,000 mu. Due to the loss of vegetation protection, more than half of Jilantai Salt Field, the largest lake salt production base in China, has been buried by quicksand. In order to prevent sandstorms, since 1980, Manshuitan Village in Jiuquan City has planted more than 20,000 trees in Nantan, built Nantan Forest Farm, and gradually improved the land once hit by sandstorms. However, since 1998, more than 4000 poplar trees have been cut down wildly, and only 4000 poplar trees remain in the forest farm in 200 1 year. After the trees in Manshuitan village were cut down, the land has begun to desertification, and the improved land is threatened by sandstorms again. The wind rises slightly and quicksand flies.
(e) Unreasonable use of water resources
The proportion of agricultural irrigation in the western region is significant, and the area of agricultural and forestry land continues to increase, which leads to the increase of water demand and the intensification of water shortage contradiction, especially in the downstream areas. In addition, the groundwater in this area continues to be overexploited, which leads to the continuous decline of groundwater level in the western region. For example, the annual decline rate of groundwater level in various water sources in Guanzhong area of Shaanxi Province is more than 2 meters. The decline of groundwater level directly leads to the decrease of surface vegetation and the acceleration of land desertification. According to relevant research, it is more suitable to maintain the ecological environment in arid and semi-arid areas, and the groundwater depth is 2 ~ 4 meters, otherwise the normal water use of natural plants will not be achieved. For example, in the Tarim Basin, the 246-km-long Tarim River below Britain and the Soviet Union was cut off in 1972, and the groundwater level in the south of Arakan dropped from 3m~5m ~ 5 m in the 1950s to 6m ~1m, which exceeded the groundwater level on which plants depended. Here, the forest lost its regeneration ability, and the young trees could not grow and died in pieces. The decrease of surface plants has accelerated the desertification of land. From 1958 to 1993 in the lower reaches of Tarim River, the area of mobile sand dunes increased from 44.34% to 64.47%, and the intensity and extreme intensity of desertified land increased by 3. 12% and 3.56% respectively.