The Research Of The Vegetation Change And The Sensitivity Between NDVI And Climatic Factors In Qilian Mountains From2000to2012

As the best instruction factor of vegetation coverage, NDVI is regarded as themost effective indicator to monitor regional or global changes of vegetation andecological environment. Based on MODIS NDVI data with spatial resolution of250mand climate data from2000to2011, this article studied the spatiotemporal variationof growth vegetation changes and its correlation with climatic factors in the QilianMountains which is analyzed by using the maximum value composites method、average method、trend line analysis method and correlation analysis method. It willhave profound significance to research the vegetation cover change and its responserelation with the climatic factors of Qilian Mountains for the region land usecharacteristics as well as for regional and global climate and environment change.The results show that:(1) In Qilian Mountains, the vegetation coverage increased gradually from thewest to east; the distribution of the vegetation coverage in the eastern parts werelarger than that in the western parts; the tendency of the vegetation coverage increasedgreatly in recent13years and the trend of the vegetation coverage of every month ingrowing season increased as well, the biggest increase in May, July take second placeand smallest increase in August; precipitation increasing caused by global warmingwas the main reason of the vegetation coverage increasing, and the increasing trend ofthe vegetation coverage in spring is the most obvious, the vegetation coverage inautumn take second place.(2) There are some significant spatial differences of the vegetation coveragechanges in different seasons, the increased area of vegetation in summer is the largestand the area is91669km2which accounted for48.7%of the total area, mainlydistributed in Qinghai nanshan, the valley of Buha and Huangshui river, Danghenanshan, Shule nanshan, Tuole nanshan, Corridor nanshan and other places; and thearea of decreased vegetation coverage accounted for13.7%of the total area, mainlyconcentrated in Daban mountain, Datong mountain, Tuolai mountain, Lenglong ridge,Wushao ridge, Datong river basin and other place at the eastern parts of QilianMountains. The area of increased vegetation coverage was83779.75km2whichaccounted for40.9%of the total area in spring and mainly distributed in the southern of Qinghai lake, Laji mountain, Buha lake basin, Datong mountain, Daban mountainand Qinghai nanshan; the area of decreased vegetation coverage accounted for18.8%of the total area which mainly concentrated in Lenlong ridge, Corridor nanshan,Wushao ridge, Tuolai nanshan, Shule nanshan, Daxue mountain and other place. thearea of increased vegetation coverage in autumn which mainly distributed in Lajimountain, Qinhai nanshan, Danghe nanshan, the vally of Huangshui and the area ofdecreased vegetation coverage which mainly distributed in Lenlong ridge, Wushaoridge, Daban mountain, Datong river basin, Tuolai nanshan, Shule nanshan andCorrider nanshan. The decreased area of vegetation in winter is the largest and thearea is55501.75km2which accounted for29.5%of the total area, mainly distributedin Wushao ridge, Lenlong ridge, Daban mountain, Tuolai mountain, Corrider nanshan,Daxue mountain and Hala lake basin; the increased area of vegetation distributed inQinhai nanshan, Laji mountain and other place.(3) In Qilian Mountains, there are some significant spatial differences of thevegetation coverage changes just like it increased in the middle and western parts ingrowth season, meanwhile, it decreased in the eastern part; the area of increasedvegetation coverage was79149km2which accounted for52.93%of the total area,mainly distributed in Laji shan, Daban mountain, Toler nanshan, Shule nanshan,Qinghai nanshan, Lenglong ridge, Tuolai nanshan, Corridor nanshan, Danghenanshan, Xining basin, as well as the valley area of Qinghai lake, Hala lake andHuangshui; and the area of decreased vegetation coverage was22865km2whichaccounted for11.09%of the total area respectively, mainly distributed in Wushaoridge and the valley of Shiyang river, Heihe river, North river, Shule river.(4) There are obvious differences of the time lag effect between NDVI andclimate factors in different seasons in Qilian Mountains. The correlation coefficientbetween NDVI and temperature in spring is the highest and the correlation coefficientis0.721, the correlation between NDVI in spring and precipitation at different periodsis low; the correlation coefficient between NDVI in summer and the period ofprevious and cumulative precipitation is the highest, it states that NDVI in summerand precipitation in spring has a certain lag correlation; the correlation coefficientbetween NDVI in autumn and the temperature in the same period is negative, and there is a lagged relationship between NDVI in autumn and precipitation in summer,but the lag effect is not obvious; the correlation between NDVI and precipitation inwinter is negative and the correlation coefficient with temperature is positive, as wellas with the temperature in the same period is higher.(5) The relevance between vegetation NDVI and temperature, precipitation ishigher in growth season in Qilian Mountains, there is also a lag time between them.The lag time between NDVI and precipitation in June and July respectively are oneand two month, the correlation coefficient are0.788,0.684, The lag time betweenNDVI and temperature in August and September respectively are zero and one month,the correlation coefficient are0.825,0.829.(6) The spring vegetation growth was mainly affected by temperature, thecorrelation with temperature and NDVI in Daban mountain, the valley of Datong riverand Huangshui river is significant, the correlation between NDVI and precipitation inspring is low at the eastern parts and the correlation is negative at the middle andwestern areas; the correlation between NDVI and temperature in summer is negativecorrelation and the temperature and NDVI in Daxue mountain, Danghe nanshan andsome parts of Lenglong ridge is uncorrelated, the correlation between NDVI andprecipitation is the highest and in most of the western region was significantlycorrelated to the NDVI and precipitation; the correlation between NDVI andtemperature, precipitation in autumn is low and correlation coefficient in Lajimountain, Lenglong ridge and Huangshui valley are the highest; the correlationbetween NDVI and temperature in winter is low as well as with precipitation has asignificant negative correlation.(7) The correlation coefficient between NDVI and temperature in growingseason at Trgdaban mountain, Danghe mountain, the east of Daxue mountain, thenorthwest of Tuolai nanshan, Wushao ridge achieve significant correlation, thecorrelation between NDVI and precipitation in Laji mountain, the east of Qinhainanshan, the east of Wushao ridge and the surrounding region of Qinhai lake achievesignificant correlation and the correlation coefficient is0.698; but the correlationbetween NDVI and precipitation is unobvious in the northeast of Qilian mountains,Daxue mountain and Danghe basin and the correlation is low, the correlation between NDVI and precipitation, temperature at the edge of Qilian mountains under3000meters above sea level are low.