Study On Eco-environmental Fragility And Assessment In Upper Reaches Of Minjiang River

With the degradation of eco-environment, the restoring and rehabilitating of regional ecological and economic system have attracted more and more attention in China. The upper reaches of the Minjiang River is an important economic protective to Sichuan province and the west of China, while the eco-environmental fragility in this region has endanger the Changjiang River basin and been main restrictive factor of economical development. The research of the eco-environmental fragility in upper reaches of the Minjiang River is important to guide not only the restoring and rehabilitating of regional ecological system , but also the sustainable development of this region.The upper reaches of the Minjiang River area include Wenchuan, Li county, Mao county , Songpan and Heishui county, the total area is 25426.875km2. This region is a typical fragile ecological system based on dry valley. The eco-environmental fragility displays in these respects: soil erosions increases, water and soil loss seriously, forest decreases, ecological function reduces, dry valley increases, disasters happen frequently, amount of the river runoff reduces, hydrological changes violently, grassland deteriorate seriously. Eco-environmental fragility is caused by the nature fragility and people action. This article has done the research on the main cause about eco-environmental fragility of the upper reaches of the Minjiang River, analyzed the evolution processes of climate, forest, people action, population vary, land utilization, and etc.To research the happening mechanism and changing regularity and to set the basis of searching the methods of recovering and rebuilding, this paper especially decides 20 influencing factors and 25 specimen years(2500 data in total) and it adopts the methods of factor analysis and so on. This paper researches in the occurring mechanism and driving power and initially determines the 6 driving factors which are influencing eco-environmental fragility, that is soil running off condition, industry structure condition, land utilization condition, investment level and structure condition, population bearing condition. It is showed from the time alternativeness of regional eco-environmental fragility, due to the structure fragility and forcing fragility's common effect. Before 1985, the upper reaches of Minjiang river's fragility was worsening continuously. After 1985, we put more and more attention to protection of eco-environment, and the action of humanbeing are confined. So forcing fragility has descended. The upper reaches of Minjiang river now mainly are influenced by structure fragility, comprehensive fragility also shows stable condition. This paper analyze the upper reaches of Minjiang river fragile special distribution pattern And then it concludes that the fragility is weakened from the dry valley region to south and north. Therefore, the problems of the upper reaches of Minjiang river fragility result from nature and human effect.The comprehensive assessment of the eco-environmental fragility in upper reaches of Minjiang River is a pattern recognition problem. Combined with the result of ambiguity assessment, this article applies creatively the techniques of artificial nervous network and projection for seeking trace, which have been applied extensively and developed very fast in pattern recognition, to overall quantitatively analyze and assess the upper reaches of Minjiang River. Through the results above all, it is obvious that the eco-environmental fragility in upper reaches of Minjiang River is fragile very much, and especially in the structure fragility indexes of drying degree index-, evaporation coefficient, deteriorated grassland, desert rate, the forest covering rate, and etc, which seriously restricts the eco-environmental equality and the human action intensity of this region. Based on which have been mentioned so far, this article aims at all the problems and puts forward the principles and measures of the restoring and rehabilitating in upper reaches of Minjiang River, mainly including returning land...