Studying Of Vegetation Spatiotemporal Variations On Qinghai-Tibet Plateau Based On Remote Sensing Vegetation Index

Terrestrial ecosystem is an important part of land surface and provides various supports for human survival and development.As a transit point for material exchange between biotic and non-biotic elements in the terrestrial ecosystem,vegetation growth is sensitive to climate change and also plays an important role in regulating climate and environment.The Qinghai-Tibet Plateau is a unique landform and climatic region on earth surface with some alpine vegetation communities are very sensitive to global changes.Due to the large area,the complex terrains,and various climate conditions,the variety of vegetations in different regions of Qinghai-Tibet Plateau have different responses and sensitivity to climate change.It is of great significance to study the spatiotemporal variations characteristics of vegetation by integrating various factors and analysis methods to obtain information of ecosystems structure and function and predict climate change.The paper discusses the spatial distribution,inter-annual variability and spatial autocorrelation of vegetation under three division systems which include land cover,altitude and eco-geographic regions using pixel statistics,least squares linear regression and spatial autocorrelation.Two remote sensing datasets,GIMMS AVHRR NDVI3 g from 1981 to 2015 and MOD13A3 from 2000 to 2019,is the representation of vegetation growth and CNLUCC dataset,SRTM DEM 90 m data and ecological geographic vector boundary is used for division.The conclusions are as follows:(1)Vegetation NDVI in is relatively homogeneous in the same division part but obviously different between different division parts;(2)Variations of vegetation on Qinghai-Tibet Plateau did not prominent from 1981 to 2015,and the area of improved vegetation was slightly larger than that of degraded vegetation.While the vegetation generally showed as improvement and the degraded area was small from 2000 to 2019;(3)From 1981 to 2015,the vegetation of higher NDVI values in regions with low altitude and humid climate was significantly degraded,and the vegetation of lower NDVI values in regions with high altitude and arid climate improved slightly.The average NDVI of all vegetation zones showed an increasing trend from 2000 to 2019.An inflection point of mean NDVI variation in vegetation division occuered around 2000;(4)There was strong spatial autocorrelation of vegetation on Qinghai-Tibet Plateau which often affected by the growth and aggregation of high-coverage vegetation variation;(5)The spatial autocorrelation between GIMMS NDVI and MOD13A3 NDVI showed greatly difference in regions that vegetation growth well,and spatial autocorrelation of GIMMS NDVI was stronger;(6)Vegetation spatial autocorrelation has two variation inflection,1993 and 2006.The change of vegetation gradually developed from random positions to the entire area.And vegetation migrated along the boundary of eco-geographic regions with the change of climate distribution pattern;(7)The area of cold spots decreased and the area of hot spots expanded from 1981 to 2015.While from 2000 to 2019,and the randomness of vegetation spatial distribution increased due to the decreasing of both cold spots and hot spots.And inter-annual variations of vegetation at the boundaries of eco-geographic regions show obviously spatial dependence.