Temporal And Spatial Analysis Of NDVI Variation And Correlation Analysis Between NDVI And Temperature And Rainfall In The Natural Grassland Of Qinghai Province

Qinghai province ranks the five greatest grazing land of China,and it's natural grassland is over 3417ha,which is up to 49.3%of Qinghai total territory.It is not only the physical foundation of the local economical development,but it also plays an important role in maintaining the regional ecological balance and in the civilization of local minority nationality.The time series data of NOAA/AVHRR from 1982 to 2003,the vector data of Qinghai grassland type,monthly temperature and rainfall data of the same periods, DEM of this area are used in the study.Under the support of ENVI,ArcGIS and Anusplin,the seasonal and inter-annual feature of the NDVI variation were discussed in the article,the spatial trend distribution of Mean NDVI,mean temperature and mean rainfall over 22 years were analyzed in the study.Furthermore,the correlation analysis between NDVI and temperature and rainfall are also included in the study. The major conclusions draw from this study as follows:1)For all types of natural grassland,the NDVI value begin to increase greatly in May,and reaches to the max.in the second half of Jul.or in the first half of Aug. From then on,the NDVI value begin to decrease sharply,and in the first half of Nov., the NDVI value naturally back to the level of May.It is the reflection of natural grassland green and scorch time.2)Despite of the seasonal and inter-annual variation difference of all kinds of grassland type,the feature of Monthly mean NDVI,yearly mean NDVI,and max. NDVI of 5 types of grassland is same.the NDVI descending order is as follows: alpine meadow,mountain dry steppe,plain meadow,alpine dry steppe,mountain dessert.Compared with 80's,the fluctuation of NDVI in the 90's is enhanced.3)The correlation coefficient between Monthly mean NDVI and monthly mean temperature is 0.82;the correlation coefficient between Monthly mean NDVI and monthly mean rainfall is 0.89.The descending order of correlation coefficient of mean NDVI and temperature and rainfall is as follows:alpine meadow,mountain dry steppe,alpine dry steppe,mountain dessert,plain meadow.4)Mean NDVI of Qinghai natural grassland cover the scope of 0.075～0.43.The increase rate of NDVI from 1982 to 2003 is 0.0005/a.The increasing area and decreasing area of NDVI coexist.But the increasing amplitude is larger than the decreasing amplitude.The greatest increasing amplitude is 0.105/22a,the maximal decreasing amplitude is 0.068/22a.and there exist 4 NDVI decreasing area:①Yushu prefecture:TuoTuohe,Zhaduo,Zhiduo and southern part of Yushu county;②Guoluo prefecture:southern part of Dari county③Hainan prefecture:on the border of Gonghe county,Xinhai county and Guinan county(namely Long Yangxia reservoir area);④Qilian mountain area.5)The result of trend analysis of temperature and rainfall indicated that the temperature increasing rate covers the range of 0.018～0.145℃/a,that the rainfall change rate is between -5.32 and 2.01mm/a.On the whole,as to the lower temperature area,such as SanJiangyuan area QiLian mountain area,the ascending amplitude of temperature is relatively low.While in the middle range of the study area,the temperature is higher,and the rise amplitude is higher too.As to the rainfall, the rainfall in Southern Qinghai is larger than the north part of Qinghai,and the corresponding rainfall descendent amplitude is also relatively larger in southern area.6)There exists positive correlation between yearly mean NDVI and yearly mean temperature,and the coefficient is up to 0.59;But the correlation between yearly mean NDVI and yearly mean rainfall is -0.25(not significant).As to the spatial distribution,the positive and negative correlation area between NDVI and temperature coexist,so does NDVI and rainfall.Under the circumstance of temperature ascending speed covers 0.018～0.145℃/a,the NDVI will go down in the negative area of NDVI and temperature.The trend analysis of temperature and NDVI have proven this point of view.On the other hand,in the positive area of NDVI and temperature,the NDVI will go down or go up depending on the both of rainfall and temperature.7)The trend analysis of NDVI,temperature and rainfall suggested that the climate change will cause different influence on the different grassland in the certain area.In the future,the NDVI value in the Qilian mountain area and Dari will increase. But in the area of Long Yangxia reservoir area,the NDVI value will decrease further because of enhanced drought.