Remote Sensing Monitoring And Analysis Of Vegetation Cover Change In The Heihe River Basin From 2000~2012

The ecological environment has a close relationship with the survival and development of human society. Vegetation ecosystem plays a decisive role in terrestrial ecosystems and it faces enormous challenges with the global climate change. Alpine area is regarded as one of the most sensitive areas of global climate change, my research area is located in the northern foot of the Qilian Mountain where the sea level elevates from 1500 m up to 5500 m. This area is affected by southeast monsoon and west-wind drift, its precipitation and temperature is greatly varied with seasons and ecological environment is extremely unstable. The upstream of the Heihe River Basin is the major water source for industrial and agricultural production in the middle section of Hexi Corridor, and is also for the existence of the oases in the downstream. Therefore monitoring and analyzing the variation of vegetation coverage in this area by remote sensing technique and studying the distribution characteristics of protection zone of vegetation are of significant importance for protecting its ecological environment.This paper focused on the vegetation coverage in the mountainous area of upstream of Heihe River Basin by applying remote sensing and GIS techniques on MODIS NDVI data, DEM data, soil data, land use types data and meteorological data. I estimated the surface vegetation coverage from 2000 to 2012 by pixel dichotomy, analyzed the correlation between vegetation coverage and climatic factors, the seasonal and annual variation characteristics of vegetation coverage, and the relationship between vegetation coverage and terrain factors. In addition, I categorized the research area into five grades in terms of change span of vegetation coverage, they are no change, low change, medium change, medium-high change, and high change, respectively. And the vegetation protection area is further delimited on the basis of this category.The vegetation coverage in research area is bounded into two parts by, from the East to the West, the Malian gully——Guogai gully——Dahong gully ——Henan platform. To the north it is characterized of low and low-medium vegetation coverage and to the south it is medium to high vegetation coverage. The boundary shifts back and forth on both sides as the seasons change. From spring to winter, the curve of the ratio of areas occupied by the low and high vegetation coverage shows a “n” type, while the one of low-medium, medium, medium-high vegetation coverage presents a “u” type. The primary variation of the area of vegetation coverage is taken place from spring to summer, the second variation is from autumn to winter, while the least is from summer to autumn; The maximum vegetation coverage is in the range of 3000m-3500 m, the average of vegetation coverage increases with the increasing slope gradient. The fastest increase of vegetation coverage is in the southeast slope, while the slowest is in the north slope and the northeast slope. The vegetation coverage of the research area basically maintains unchanged from 2000 to 2012, and the increased area is greater than the reduced area; the stability of vegetation coverage decreases year by year. The worst regions are approximately 3100km2, mainly located in the upstream of the Toler River, of the Heihe River and of the North River. These areas are the key protection regions of vegetation.