Spatial-temporal Variation Of NDVI And Analysis Of Climate Response In The Source Region Of The Yellow River From 2000 To 2014

(1)In the source region of the Yellow River, the tendency of the vegetation coverage increased greatly in recent 15 years.On the season, the summer vegetation growth rate is the largest, the second is the average annual vegetation; on vegetation types, the largest growth rate is alpine grassland. The distribution of the vegetation coverage decreased gradually from southeast to northwest. vegetation coverage is the best in the east of the source region of the Yellow River and Ruoergai Basin, the main types of vegetation coverage are alpine meadow and alpine swamp; the annual cumulative average NDVI is the second, in the central of the source region of the Yellow River, the main vegetation types are alpine shrub, needle broad-leaved forest and alpine meadow.In the northwest of the Yellow River source area, the vegetation coverage is less, the main vegetation types are alpine steppe, alpine meadow,and a small amount of alpine vegetation.(2)In the source region of the Yellow River, the tendency of temperature and precipitation increased greatly in recent 15 years.The maximum rate of temperature increase is spring with a rate of 0.0677 ?/a, The maximum precipitation increase rate is average annual NDVI with 6.712 mm/a.(3)The significant horizontal spatial distribution of average annual NDVI and temperature and precipitation is consistent with the significant test results of that.Only the alpine meadow and coniferous broad-leaved forest pass the significant test, in the correlation test of temperature and NDVI of different vegetation coverage types. Positively related to vegetation type is mainly alpine meadow and broad-leaved forest, In the spatial distribution of annual NDVI and temperature. Alpine meadow, needle broad-leaved forest and alpine grassland pass the significant test, only alpine grassland pass the significant test of 0.01, in the correlation between NDVI of different vegetation coverage types and precipitation. In the significant horizontal spatial distribution between annual NDVI and precipitation, extremely significantly positively correlated vegetation is alpine grassland, significantly positively correlated vegetation is alpine swamp. Alpine meadow and needle broad-leaved forest is mainly the impact of temperature.It is show that alpine meadow and needle broad-leaved forest is mainly the impact of temperature, alpine grassland and alpine swamp is mainly affected by precipitation.(4) The driving effect of NDVI is different by climatic factors, because of its unique natural conditions.NDVI is mainly influenced by precipitation in the north of the source region of the Yellow River. As It is close to the Qaidam Basin which is arid climate, high temperature, water shortage, low soil moisture content, the vegetation growth is limited by moisture, the increase of precipitation can promote the photosynthesis of plants, the increase of precipitation can promote vegetation growth, while the temperature increases may enhance the evaporation of water and will exacerbate the trend of drought. The vegetation is mainly influenced by temperature factors in the southwest and central of the source region of the Yellow River. As it is the high altitude areas which has high soil moisture content, the growth of vegetation will not be restricted by the water condition and the increase of precipitation may also cause regional cloudiness, vegetation photosynthesis will be limited and the increase of temperature can promote the photosynthesis of plants.