Causes of Land Desertification in Northwest China

Evolution of water resources under the background of climate change

Northwest China is an arid and semi-arid region with vast land, but relatively poor water resources, which is the main limiting factor for local economic and social development and ecological protection. Under the background of global climate change, what will happen to the water resources in northwest China in the future? This is not only an important scientific issue, but also of great practical significance for planning local development strategies.

Shi Yafeng has done a lot of research on the changes of climate and water resources in northwest China. He thinks that the arid area in northwest China was in the process of climate drought and water resources shrinking in the 20th century (Shi Yafeng,1995; 200 1), while the climate in the northwest and west of Wushaoling and Sun Moon Mountain changed from warm and dry to warm and wet in the late 1980s (Shi Yafeng et al., 2002). In June, 2005, at the meeting of "Science and China" in Lanzhou, he further clarified the following views: "With the increase of precipitation and glacial meltwater in the future, the runoff or surface water resources in the northwest and Qinghai-Tibet Plateau will also increase, and the drought in the northwest and Yellow River source areas will turn into rainy season, but the specific wet year cannot be accurately predicted" (Song Hualong, 2005).

Since the end of 1980s, precipitation in the west of northwest China has been increasing, which has been confirmed by meteorological and hydrological data (Liu Chunqi, 2000; Ren Guoyu et al., 2000; Zhou et al., 2005). However, there are different understandings about the changing trend of evaporation after heating. Some studies think that surface evaporation will increase, while others think that evaporation will decrease (Ren Guoyu, 2005). In particular, the comprehensive impact of the runoff changes of ice and snow belts and forest belts in the inland river basin caused by warm and humid (or warm and dry) climate changes on the total runoff changes in mountainous areas needs further discussion.

At present, one of the biggest obstacles to answer this question is the lack of comprehensive observation (model simulation) in different mountainous areas to meet the research needs. In the future, on the basis of strengthening the observation of runoff changes in snow and ice belts and forest belts, we will focus on the following issues: (1) Climate change of warm, dry and warm humidity in northwest China on the time and space scale; (2) Under the background of climate change, how will the evaporation in northwest China change? (3) The overall impact of climate change on the runoff changes of snow and ice belts and forest belts in mountainous areas.

The second is the coordination between ecological water use and production and domestic water use.

Watershed ecological water demand refers to the amount of water resources that must be stored and consumed in order to maintain the normal ecological and environmental functions of the watershed (Liu Changming, 2004). For a long time, due to insufficient attention to ecological water demand, the phenomenon of over-exploitation and utilization of water resources in arid areas of northwest China is widespread. The ecological water demand has been squeezed a lot, and the quality of ecological environment has deteriorated very seriously. Such as Tarim River, Heihe River and Shiyang River, due to the excessive development and utilization of water resources, the water resources in the lower reaches of the rivers have dropped sharply, the rivers have been cut off, lakes and swamps have shrunk (taitema lake, Juyanhai and Qingtu Lake have dried up), the groundwater level has dropped, and vegetation (Populus euphratica, Salix psammophila, etc.). ) has died and the biological habitat has been broken and disappeared.

In the arid area of northwest China, water has become a key factor to maintain the ecosystem due to the scarcity of precipitation. Only in mountainous areas with more rainfall and on both sides of rivers in plains can there be better vegetation distribution. The contradiction between production, domestic water use and ecological water use in northwest China is very prominent. In order to solve this contradiction and rationally allocate the water consumption of the two, a key problem is the quantitative estimation of ecological water demand.

The common methods for estimating ecological water demand are: (1) traditional hydrological flow calculation method (standard flow method); (2) Hydraulic method based on hydraulics; (3) Biological habitat method based on biology. However, there are still many problems in the traditional estimation method of ecological water demand in northwest inland river basin. For example, how to determine the suitable ecological water level downstream? What does it have to do with coastal vegetation growth? What does it have to do with the water level and flow of rivers? To what extent should Tail Lake be protected? How to determine the water demand? What is the relationship between the change of natural oasis and river water quantity? What is the relationship with flood discharge and inundation range? Wait, the existing methods are difficult to determine. Lack of sufficient observation data is also one of the important reasons.

The key scientific research work in the future includes: (1) strengthening the study of eco-hydrology, especially the study of the regularity of the relationship between water and ecosystem changes; (2) Combining the allocation of ecological water, production water and domestic water with river basin water cycle and water balance; (3) Comprehensively study the ecological, environmental and economic effects under different water resources allocation.

Third, grassland degradation.

According to the measured quadrat data in the northern region, the total grassland area in the five northwestern provinces is119.75 million ha, and the total degraded grassland area caused by various factors is 69.6 million ha, accounting for 58% of the total grassland area. Among them, the lightly degraded area is 30.209 million hectares, accounting for 43.4% of the total degraded area; Moderately degraded 26.507 million hectares, accounting for 38% of the total degraded area; The severely degraded area is 654.38 028900 hectares, accounting for 654.38 08.5% of the total degraded area. Compared with the investigation results in the 1980s and 1990s, grassland degradation has a tendency of aggravation (Hong Maozeng, to be published).

How to control grassland degradation and take the road of sustainable grassland animal husbandry management in arid areas of northwest China is the focus of debate: should it be extensive or intensive in fragile areas of northwest China? Is it natural rotational grazing or large-scale settlement (Li Xianglin, 2002)? The viewpoint supporting intensification holds that (1) intensive grassland animal husbandry production is the development direction of modern grassland industry; (2) Artificial grassland construction is an effective way to solve the problem of stable forage source for livestock; (3) Artificial grassland construction is beneficial to grassland management; (4) It can reduce the pressure of natural grassland; (5) It is beneficial to community construction and education development in grassland areas. However, the viewpoint supporting extensive production holds that (1) nomadic and seasonal migration modes of production are the crystallization of thousands of years' wisdom of herders in almost all animal husbandry areas in the world (including grassland areas in northern China), which accords with the characteristics of uneven spatial distribution and large seasonal differences of grassland resources in northern China. However, high-intensity grassland animal husbandry production in arid areas of north and northwest China is more likely to cause grassland degradation; (2) Australia and other countries, similar to the arid inland areas in northwest China, also implement extensive management methods and do not advocate intensive production; (3) Large-scale artificial grassland construction consumes soil moisture and causes soil dryness (Wei Yongsheng et al., 2004).

In fact, it is the right choice to adjust measures to local conditions and rationally allocate intensive and extensive management in space. However, to achieve this, there are still many scientific problems to be discussed: (1) How to reasonably determine the grazing "pressure" and calculate the grassland carrying capacity in northwest China with large fluctuations in climate season and year? In particular, how to choose a reasonable management model according to the temporal and spatial changes of grassland carrying capacity? (2) How to comprehensively consider grassland degradation and herdsmen's livelihood, and reasonably determine the proportion of operational grassland and protective grassland area?

Four. Sandstorm disaster and desertification

The aggravation of sandstorm disaster in northern China in 2000 and the following years has aroused people's extensive concern about the ecological situation in China, and it is also one of the main driving factors for the government to increase investment in ecological construction projects. However, to what extent is the intensification of sandstorms caused by human activities in recent years? Or how much does it have to do with desertification? And to what extent is it related to climate fluctuation? Scholars have different opinions.

The focus of the debate is the source and development trend of sandstorm. As for the source of sand dust, the theory of human activities leads to a low percentage of sand dust in the desert, and only 5% of sand and clay are in the sand flow of quicksand. Therefore, it is inferred that the material source of dusty weather is desert land on the edge of desert. According to the theory of climate fluctuation, the low dust content in quicksand does not deny that the main material source of dusty weather is desert, and not all desert landscapes are quicksand with a lot of fine materials. The desert and Gobi are constantly producing fine substances, and its mechanism is still unclear.

With regard to the development trend of sandstorm weather after the founding of the People's Republic of China, the theory of human activities is mainly based on the intensity of media reports, and sandstorm weather has an increasing trend in the 1950 s and 1990 s; Scholars who hold the theory of climate fluctuation think that this statistic is not comprehensive enough. According to the record of North 68 1 weather station, during the 45 years (1954- 1998), except for Zhu Rihe and Haixing Station (Zhou Zijiang, 200 1), all three kinds of sandstorm weather (sandstorm, sand blowing and floating dust) showed a weakening trend.

Understanding the source and formation mechanism of sandstorm determines what countermeasures and measures should be taken to deal with this natural disaster. The key problems to be studied in the future include: (1) the formation mechanism of desert fine matter; (2) Quantitative monitoring of dust sources; (3) Regularly draw desertification land change maps with uniform standards.

Verb (abbreviation of verb) is a deep-seated problem that needs overall coordination in ecological construction.

Nature is an organic whole formed by the close contact and interaction of various elements, and the interests of all parties using natural resources and ecological services are different. Only by coordinating the contradictions and conflicts between industries, between urban and rural areas, between upstream and downstream, between natural ecology and human development, and between short-term interests and long-term interests can we truly embark on the road of sustainable development. At present, the deep-seated problems that need to be coordinated in the ecological construction in northwest China are mainly manifested in the following aspects:

(1) The policy of forbidding grazing and returning farmland and the overall livelihood of farmers and herdsmen. People living in the northwest farming and pastoral areas are generally poor, and there are few employment opportunities outside the farming and pastoral areas. Their livelihood mainly comes from agricultural and pastoral areas, that is, the utilization of ecosystem productivity. It is doomed that there are contradictions and conflicts between the development of agriculture and animal husbandry and ecological protection, especially in dry years, it is difficult for farmers and herdsmen with productive land to make a living, and it is very difficult to implement "grazing prohibition" in some areas.

(2) The "one size fits all" problem in the implementation of ecological construction measures. Northwest China has a complex environment and great regional differences, so ecological construction should be adapted to local conditions. However, this is difficult to manage. Afforestation, pasture introduction, artificial grassland cultivation and grassland restoration in many areas all violate the principles of zonality and local conditions, resulting in a "one size fits all" phenomenon, which violates the laws of natural ecology and brings damage to the development of agriculture, forestry and animal husbandry.

(3) Coordination of interests between regions, especially between upstream and downstream. The basin is a whole with complementary and interrelated functions of the upper, middle and lower reaches. However, in the utilization of resources, especially the scarce water resources in northwest China, and the environmental effects of industrial development, there are often conflicts of interest between the upstream and downstream of the basin. Without the joint efforts of the upper and lower reaches of the river basin, it is impossible to improve the overall ecological quality in northwest China.

(4) It involves the coordination of ecological construction departments (agriculture, forestry, water conservancy, soil and environment). Nature is a whole, and any human activity has many influences on nature. However, the government can only manage the natural environment, resources and ecology by departments. All departments hope to make more contributions to ecological construction and do more work. Sometimes, the comprehensive characteristics of nature and departmental management will conflict. For example, for some areas and some ecosystems, natural restoration may be the best way. Only the coordination among agriculture, forestry, water, soil and environment can achieve the goal of ecological protection.

In view of the above problems, we should strengthen the interaction between resources and environmental science, economics and law, and strengthen the comprehensive study of the relationship between man and land. Social scientists should actively explore the root causes and key links of economic and social conflicts, and natural scientists should provide accurate evaluation information for key natural science problems. Only through the cooperation of natural science and social science can we find effective and feasible ecological construction strategies.