Ecological Risk Assessment And Forecast Of Gannan Rangeland

Gannan state is a poll of forage in the western part of China, which holds a unique ecological environment and a large rangeland. The rangeland is not only ecological resources but also economy base of nomads. However, special physic geographic condition together with unreasonable behavior of human cause rangeland deterioration, the ability of water conservation reduction, soil erosion aggravation and make various disasters more common, which restrict the development of agriculture and animal husbandry seriously. In this paper, the theory of vegetation index dynamic changes was introduced to grassland classification in Gannan state, and the result of classification was used as risk receptor. In addition, grassland aboveground biomass, on the base of PVI which is good at weakening the effect of soil, was chosen as ecological endpoint. According to almanac and probability, intensity and influence range of risk, five risks was selected. Among them, two (grazing overloaded rate and urbanlization) are anthropic factors and three (snowstorm, soil erosion and extreme change of climate) are natural damages. Finally, principal component analysis was adopted to calculate the weight of risks, which lead us to obtain synthetical harm of rangeland through 2001 to 2009. The result shows that:the ecological risk intensity of Lintan County is the highest one among all the counties, and the intensity of 9 year almost remains the same; the risk strength of Zhouqu County is a little lower than that of Lintan county, and that of Hezhuo City is a little lower that of Zhouqu County, and the risk intensity of Zhuoni County is the lowest of all the counties, moreover, the risk strength of this three counties was trending up but not changed a lot; however, the ecological risk intensity of Diebu County extremely rised through first level to the fifth level among 9 years; the risk strength of Luqu County also increased a lot but not as that of Diebu; among all the counties, risk intensity has a large irregular change because of snowstorm. The prediction result indicates that risk intensity of Lintan County is the largest; the intensity of Zhouqu County is a little lower than Lintan; that of Zhounni County is the lowest and that of Maqu county, Luqu County, Diebu County and Xiahe County is medium; the intensity of Hezuo City is a little larger than the four counties above.