Change Characteristic Of Vegetation NDVI And Its Response To Climate Change In Qilian Mountains

As the best indicators of the vegetation growth conditions and vegetation coverage, Normalized Difference Vegetation Index(NDVI) is also the most effective regional or global indicators for monitoring vegetation and ecological change. Study on the change of vegetation NDVI and its response to climate factor are important to land use, regional and global climate change and environmental change in Qilian Mountains. Based on the data of GIMMS NDVI for 8km from 1982 to 2006 and MODIS NDVI for 1km from 2000 to 2014 provided by NASA and the meteorological data of 37 meteorological stations in conjunction, average annual growing season, different seasons, different spatial and temporal changes of vegetation types and vegetation NDVI and climatic factors relevance were studied by maximum synthesis method, average method, slope analysis, correlation analysis after like extraction and analysis of meta-information in Qilian Mountains. Research indicates:(1) Variation of NDVI in Qilian Mountains is decreasing from east to west. Maximum value of cumulative average NDVI range 3 to 5.7 in eastern Qilian Mountains where the main vegetation cover types are forest, grassland and temperate typical steppe. It ranges 2 to 3 in middle Qilian Mountains where the major vegetation types are humilis alpine shrub and alpine meadow. It ranges 1 to 2 in western Qilian Mountains where the main vegetation types are alpine and alpine desert steppe. It ranges 0 to 1 in the most western region of Qilian Mountains, where are largely bare, desert, gravel, lakes and glacier area.(2) From 1982 to 2006, vegetation improvement is the most obvious in the fall for change rate of NDVI is the largest, followed by summer and winter, but it is the smallest in spring. From 2000 to the 2014, that is the most obvious in summer because change rate of NDVI is the largest, followed by winter and autumn, while it is also the smallest in spring. On the whole, vegetation index show a decreasing trend in spring, autumn and winter since 15 years, among decreasing trend is the most evident in spring, followed by autumn and winter.(3) There are significant spatial differences about seasonal variation of vegetation NDVI in Qilian Mountains. From 1982 to 2006, the area of the increasing NDVI in spring, summer, autumn and winter are 47019 km~2, 61841 km~2, 50612 km~2 and 20445 km~2, accounting for the proportion of the total area of Qilian Mountains are 25.01%, 32.88%, 26.91% and 35.67%. The area of the decreasing NDVI in spring, summer, autumn and winter are 19974 km~2, 47508 km~2, 49953 km~2 and 67088 km~2, accounting for the proportion of the total area of Qilian Mountains are 10.62%, 25.26%, 26.61% and 10.87%. Overall, the region of vegetation increase in four season are mainly distributed in Qinghai Nanshan, Morgan Hill, Buha River Basin and other places, but the region of vegetation reduction are mainly concentrated in Wushaoling, Lenglongling, Daban Mountain and Heihe river valleys and other places. From 2000 to 2014, the area of the increasing NDVI in spring, summer, autumn and winter are 77691 km~2, 50 298 km~2, 23747 km~2 and 26164 km~2, and the proportion of the total area of Qilian Mountains are 41.31%, 26.74%, 12.63% and 13.91% respectively. The area of the decreasing NDVI in spring, summer, autumn and winter are 2558 km~2, 8887 km~2, 45312 km~2 and 17452 km~2, and the percentage of the total area of Qilian Mountains are 1.36%, 4.73%, 24.09% and 9.28%. The region of vegetation increase in four season are mainly distributed in Qinghai Nanshan and Lajishan where mainly locate high altitude region with evergreen coniferous forests and evergreen shrub, that the vegetation show an increasing trend for temperature raise of nearly 10 years.(4) From 1982 to 2006, the change trend scale of vegetation NDVI are descending desertification > meadow > steppe > shrub > alpine vegetation > vegetation cultivation > swamp > broadleaf forest > other vegetation > coniferous, that they show an increasing trend with different scale. From 2000 to 2014, the change trend scale of vegetation NDVI are descending > coniferous forest > grassland > cultivated vegetation > broadleaf forest > other vegetation > bush > alpine vegetation > meadow> swamp, that they also show an increasing trend except for other vegetation. There are differences of vegetation NDVI of different types in different seasons from 1982 to 2006 or from 2000 to 2014.(5) Monthly average NDVI significantly correlate with sunshine hours and relative humidity, and significantly correlate with temperature and precipitation very much, so temperature and precipitation are major climatic factors to changes of vegetation NDVI. The overall interannual change trends of precipitation and temperature are more similar to that of vegetation NDVI which indicate the change of vegetation NDVI is sensitive to temperature and precipitation changes. In some years, the precipitation and temperature increase but vegetation NDVI decrease, which indicate the change of vegetation NDVI exist a certain lag to change of temperature and precipitation.