Change in NDVI of northern Tibet and root cause analysis from 1982 to 2014

Vegetation growth in Nagqu exhibited an marked variation in status in the last 5 years under the grassland reform ecological compensation project. GIMMS, MODIS-NDVI, meteorological observations, and data on social statistics from 1981-2014 have been used to investigate spatial and temporal variations in vegetation along with the effect of meteorological factors and human activities on vegetation distribution. The results showed that interdecadal variations in vegetation exhibited a periodic increasing tendency, while interannual variation did not change substantially in the past 34 years. The trend showed by vegetation in most parts of Nagqu indicated a stable variation, and the areas constituted 57.82% of the total region; areas with slight improvement and decrease constituted 32.84% and 14.06%, respectively, and areas with significant variation represented 7%. Areas with serious degradation were mainly concentrated in the eastern and southeastern counties of Nagqu, while stable areas were situated to the west of the middle region and northern counties; vegetation in certain areas even tended to improve. Variations in precipitation, air temperature, and livestock density constitute the main reason for the uneven spatial distribution of vegetation in Nagqu.