Study On Ecological Environment Evolution And Driving Force In Source Regions Of The Three Rivers Based On RS And GIS Technology

Three rivers source in Qinghai-Tibet Plateau is the source region of the Yangtze River, Yellow River and the Lancang River, which has a high density of rivers, abundance of lakes and wetlands, and far-flung of mountain glaciers, known as "the river source" and " the water tower of china". However, in the context of global warming, due to the natural conditions restrictions and human activities effects, the ecological environment problems in the three rivers source have become increasingly prominent, such as the temperature raise, precipitation reduction, glaciers shrinkage, the grassland degradation, the water and soil serious erosion, and the ability of water conservation debasement, and so on. The deterioration of headstream ecological environment had negative effects on the economy and social sustainable development of the middle or lower reaches of the Yangtze River, Yellow River and Lancang River.Source regions of the three rivers were the most sensitive and vulnerable areas of ecological environment changes in Qinghai-Tibet Plateau. In recent years, the deterioration of the three rivers source's ecological environment had caused widely attention. The previous studies of ecological environment degradation in the three rivers source were mainly focused on the analysis of certain particular factor of the ecological environment degradation, such as the climate variety, grassland degradation, land use change, the vegetation coverage change and so on. In this paper, taken the ecological environment of the three rivers source as research object, analyzed the ecological environment changes from two elements that was natural factors and human factors, in which that natural factors were used to analyze the natural characters of the environment, such as the conditions of regional hydrology, vegetation, climate and so on, and that human factors mainly considered the human population and the graze activities effects on the ecological environment. In this paper, taken remote sensing and geographic information systems as technical support, on the principle of the landscape bionomics, multivariate statistical analysis, and the environment evolution of the regional differentiation, based on the space-time series analysis method to study the ecological environment variance of the three rivers source, which analyzed each factor's characters of dynamic changes, the rules of dynamic changes and development trends in spatially and quantitatively, furthermore, analyzed the mainly driving force of the ecological environment changes in the study region, in order to providing a reference to the three rivers source ecological environmental protection.Based on the multi-source remote sensing data, the thematic data and climate statistics data, extracted the elements data of ecological environment changes such as water resources, vegetation index, climate change and so on. In this paper, based on DEM data extracted the terrain factors of the gradient and slope length; making use of meteorological data to calculate the regional wetness index; and using the MODIS data combined with meteorological data based on the surface energy balance equation to estimate the regional evaporations. Based on the two periods of land use data, explored the area changes, the types of transformation and the spatial change characteristics about the land use, and combined with the landscape analysis, analyzed the changes of land use spatial patterns in study area. Based on the meteorological data, explored the characteristics of the climate changes among temperature, precipitation and evaporation. Carrying through the margin analysis, the percentage change analysis, the change vector analysis and the linear regression trend analysis, explored the spatio-temporal changes of vegetation coverage, intensity of changes, as well as the trends of changes. Making use of lakes and wetlands data in different periods, explored the spatial distribution of lakes and wetlands change intensity. Using the space-time series analysis, analyzed the climate, water resources and vegetation changes. By statistical analysis methods, analyzed the status of population changes and the human grazing activities variations in the three rivers source. Synthetically analyzed the status of all the natural environment elements changes in each district units, and attempting to analyze the influence relationship among the topography, evaporation and any other environmental factors. Finally, making use of principal component analysis, from two aspects of ecological environment changes that were the natural factors and the human activities, explored the driving force of ecological environment dynamic changes.Under the study of this paper, we can gain the following conclusions:1. The climate change laws in the three rivers source in the past 30 years: temperature in the study region presented a fluctuation upward trend, particularly in the post 2000 the temperature ascending trend enhanced obviously; the precipitation showed the changes trend of "from increase to reduction"; the regional evaporation increased evidently, and it restricted by the variations of the topography, vegetation coverage and spatial distribution of water and hydrothermal conditions, and the temperature and precipitation were the mainly influenced factors of regional evaporation; the wetness indexes of study region were between 0.20 and 0.50, on the whole, the study region belongs to semi-arid areas, and the wetness index values showed upward trend in the study region. Integrated analysis of climate changes indicated that the climate of three rivers source presented the warm and wetness trend.2. The regional land use change analysis results showed that: grassland was the main type of land use in three rivers source, and the unused land or woodland distributions less than grassland were the secondary land use type. The vegetation coverage in study region showed a significant decline, the grasslands and the woodlands reduced at a large area, and the desertification degree presented increasing trend. The landscape pattern analysis showed that the grassland was the dominant type of landscape in three rivers source, and the increasing number of unused land speckles indicated that the unused land showing a fragmentation trend.3. In three rivers source, lakes showed the trends from increasing to reducing and wetlands degraded continually, and the number of lakes and wetlands speckles increased obviously, which indicated that the lakes and wetlands fragmentation trends presented obviously, the lakes shrinking and expansion trend were evidence in the surrounding areas of Zhaling Lake and Eling Lake in the Yellow River basin, and the phenomenon of wetlands severe degradation in the Yangtze River should be paid more attention to it.4. The spatial distribution of yearly NDVI had regional differences in the study region. The NDVI value was higher in southeast region, and lower in northwest region. Based on a linear regression method, we analyzed the NDVI change trends and the NDVI increasing extents, the results showed that due to the NDVI degradation region areas accounting for a larger proportion in the study region, the vegetation coverage presented downward trend in source region.5. Integrated analysis the correlations among the ecological environment elements in the source region, the results showed that: in general, the altitude was sensitive to the conditions of temperature and precipitation; in the height of 3500 to 4000 meters, the vegetation coverage increased, lakes expansion, wetlands degradation, and human activities also focus on this height.6. The evaporation increasing was the main factor of Zhaling Lake's surface water shrinking, moreover the evaporation decreased obviously in the shrinking lakes region; but the evaporation in the Eling Lake which was a stable lake had no significant changes, indicated that evaporation was sensitive to the lake shrinking areas, and the temperature, precipitation and evaporation together affected the wetland region changes in the source region.7. The main factor of ecological environment changes in the three rivers source was the syntheses of natural factors, mainly including temperature, precipitation, lakes and wetlands of the water resources.