Guojing Yang

Analysis on driving factors of desertification in northern china: A case study of yanchi county

Taking Yanchi County as a case study, the driving factors of desertification had been analyzed. The results show that the remarkable feature of desertification of Yanchi County is the landscape changing from grassland and farmland to desert. At the same time, the fragmentation of grassland landscape is increasing continually, while the farmland is linked up on space with the decreasing landscape fragmentation. Land desertification was influenced mostly by the distribution of settlement, and the affected distance of habitation to the farmland extended gradually. Human activities and policies can dramatically change land-use patterns. Therefore, it is important to analyze the human activities and implement appropriate state policies to combat desertification in China. The conclusions of this research can provide the scientific basis of desertification control for Yanchi County and other similar regions.

Oasis land-use dynamics and its influence on the groundwater in arid Northwest China A case from terminal oasis of Shiyang River Basin

Oasis is a specific landscape, usually distributed along the sides or terminal of the inland river. In China, oases are mainly located in the deserts and gobies of arid Northwest China (1). For thousands of years, the oases have played a significant role in the development of the local economy or in maintenance of the ecological safety of China. Although the area of these oases takes up only 4–5% of the total area of the arid regions in Northwest China, more than 90% of the population and more than 95% of social wealth are concentrated within the oases (2). The oases are not only the most concentrated area of human activities in arid regions, but are also the largest area where artificial disturbances happen at the regional scale. During the last 50 years, as the population grew and cultivated land area increased, the balance between supply and demand of water has become more serious: on the one hand, the quantity of water flowing into the downstream sharply decreased; whereas on the other hand, the water requirement greatly increased in the terminal oasis, which induced excessive exploitation of the groundwater there. This resulted in some ecological problems in the downstream oases, such as descending groundwater table depth, deteriorating water quality, death of vegetation, and land desertification, and so on (3). The aims of this article are i) to report the changes of land use and detect its impacts on groundwater in Minqin Oasis, and ii) to propose some countermeasures for ecological reconstruction in the Minqin Oasis.

Variations of NDVI Over Elevational Zones During the Past Two Decades and Climatic Controls in the Qilian Mountains, Northwestern China

Abstract Trends of Normalized Difference Vegetation Index (NDVI) from 1982 to 2006 in the upper mountainous areas of three inland river basins (Shiyanghe, Heihe, and Shulehe, from east to west) in the Qilian Mountains, northwestern China, were analyzed based on the Global Inventory Monitoring and Modeling Studies (GIMMS) NDVI data. The relationships between NDVI and climatic factors such as air temperature, precipitation, and evaporation were also analyzed. The results indicate that changes of NDVI over time had an obvious elevational difference. NDVI has decreased in the northern lower-elevation (<3000 m) areas, which account for 31% of the total area, and increased in the southern higher-elevation (3000–4100 m) areas, which occupy 32% of the total area. In addition, 37% of the area did not show an obvious change in NDVI and was distributed in the periglacial belts with elevations higher than 4100 m. The decrease of NDVI in the lower elevations was controlled by a decrease in precipitation and an increase in air temperatures, whereas the increase in the higher elevations was mainly controlled by an increase in air temperature alone. With a continuous increase in air temperature in the future, vegetation would suffer from more serious water stress in the elevations lower than 3000 m, but become more flourishing between 3000 and 4100 m in the Qilian Mountains. This information is critical for understanding how climate warming may affect hydrology and ecology in the Qilian Mountains and for managing water resources for the lowlands in the Hexi Corridor adjacent to the mountains.

Dynamics of oasis landscape in inland Shule River basin in arid northwest China

Oasis is a specific landscape that exists with deserts in arid regions. In this paper, the oasis landscape changes in middle-lower reaches of Shule River basin had been analyzed. Using the Landsat TM imagines of June in 1987 and August in 2003 as the digital sources, the vector and grid landscape maps of distributions of the study area were derived. The dynamics variation of the oasis landscape in that basin was got on the basis of the software of ArcGIS 9.0, and the forecast on the dynamic variation of landscapes was executed using the software of the Matlab 6.3. At the same time, the eco-environmental effects of landscape change had been analyzed. The results showed that the landscape change with the main feature of increasing cropland area led to a series of ecological environment problem, such as deterioration of water quality, natural vegetation decreasing, and the eco-environmental system deteriorating. Human activities, especially in relation to water utilization and population increment, have gradual became the most active and dominant driving factors in the landscape change.

Impact of Land-Use Changes on Intensity of Soil Erosion in the Mountainous Area in the Upper Reach of Shiyang River in Arid Northwest China

In arid and semi-arid areas, a large area of soil erosion in the upper reaches will not only aggravate drought of atmospheric and soil, but also induce deterioration of grasslands and desertification. In this paper, as the Shiyang River upper reaches a case, we analyzed how the changes of land use and land cover influence the soil erosion, based on remote sensing satellite date and DEM, using ArcGIS software and soil erosion formula (RUSLE). The results show that: (1) the soil erosion intensity of farmland was the most serious among the vegetation types. The ability of soil and water conservation of forest, shrub and high covered grassland was the best, and which can effectively prevent the soil loss caused by the increase of slope gradient. (2) Lapping the land use changes map, soil erosion changes map and the slope map, the result indicated that reclamation high covered grassland to farmland in the areas of slope gradient exceeding 15 was the most mainly cause.

Landscape change and the driving forces in source area of Shule River in arid northwest China

Being source of Inland River in arid areas, the mountain landscape pattern influence the hydrological process, and play an important role in ecological balance. It is essential for us to understand landscape pattern dynamic changes and the driving forces to estimate the characteristics of development the landscape pattern and water resource. However, knowledge of the grassland degradation in vertical variation and the dominant factors of in arid mountain areas are largely limited. On the basis of Landsat TM images and DEM data, the changes of landscape pattern and the driving factors were analyzed in different altitude zones in the source area of Shule River. The results indicated that: The grassland in the altitude zone of 3800∼3900 m degraded markedly obvious, and the altitude where the grassland degenerated had gone upwards slightly. The most efficient driving force of grassland degradation is that the permafrost degradation caused by rising temperature.

Analysis on factors affecting the development of alpine permafrost in Central-Eastern Qilianshan Mountains, Northwest China

Using data from 190 boreholes drilled in 2004, an analysis of the factors affecting the development of alpine permafrost was carried out using the statistical analysis software of SPSS. The factors considered in this case were the terrain factors of elevation, slope, aspect, curvature, plan curve and profile curve, the climatic factors of latitude, longitude, and the potential incoming solar radiation, as well as the topographic wetness index and the vegetation abundance indicating factor NDVI. The results indicated that longitude had the most significant negative effect on the presence of permafrost. Elevation, the potential incoming solar radiation and latitude had significant positive correlations with the occurrence of permafrost.

The change of landscape pattern in arid mountain of the upper reaches of Shule River basin in Northwest China

Landscape changes are among the most important socio-economic forces of global as well as local environmental change. Mountain is a source of water in the arid regions, playing an important role in keeping ecological balance. This study focuses on the changes of mountain landscape in Shule River basin located in arid Northwest China. Based on the Landsat TM remote sensing satellite date of the study areas taken in 1986 and 2000, DEM (1:100000), using ArcGIS software, the landscape changes had been analyzed in the different elevation zones. The results show that: (1) Area of the sparse grassland is the largest in all the landscape types, the followed is rock. The vegetation of the study is 50%, and the dense grassland accounted for only 4.5%. (2) During the 15 years, the area of the dense grassland decreased 299.45 km2 because of degradation, the mid-density grassland decreased 91.5 km2. On the other hand, the area of the swamp meadow increased 168.92 km2, the freezing-throwing rock increased 101.28km2, and the sparse grassland increased 95.3 km2. (3) The grassland in lower elevation with 3500m-3800m were undergoing degeneration because of the global warming and overgrazing, and the altitude of 3500m-3800m was just the lower limit of permafrost distribution.

Response of vegetation coverage on climate change in arid mountain of Northwest China

Arid and semi-arid areas are very easily influenced by global warming because of the simple structure of landscape. The change of climate conditions affected the land vegetation coverage and its distribution in arid areas. As an indicator of vegetation growth and its spatial distribution, NDVI has a close relationship with climate conditions. Based on the remote sensing data GIMMS NDVI and software of ArcGIS, it was analyzed that the spatial-temporal correlations of NDVI with the precipitation and temperature in the Qilian Mountain located in the arid Northwest China in this paper from 1982 to 2003. The results showed that: (1) There was significant positive correlation between NDVI and temperature in the areas above the elevation of 2500 m, and significant negative correlation between NDVI and temperature in the areas below the elevation of 2500 m. (2) The value of NDVI was not visibly related with the precipitation in the both elevation areas. It can be concluded from the results that the vegetation coverage in lower elevation areas in Northwest China will be worse with the global warming.