Spatio-Temporal Variation in NDVI in the Yarlung Zangbo River Basin and Its Relationship with Precipitation and Elevation

Vegetation is a crucial indicator of climate change. Quantitative studies of spatiotemporal variation in vegetation cover as well as its relationship with topographic and climatic factors are central to understanding regional environmental change and the prediction of future tendencies. In this study,the spatio-temporal pattern of NDVI in the Yarlung Zangbo River Basin from 2001 to 2012 and variation were analyzed using MODIS monthly NDVI data,and a quantitative analysis of the relationship between NDVI with precipitation and elevation was conducted using the TRMM monthly precipitation product and SRTM DEM data. The analysis indicated that in general,NDVI increased from the upper reaches to lower reaches,and that NDVI was stable with a slow uptrend during 2001 and 2012. In the lower reaches,annual average NDVI was over 0.6,while in the upper reaches it was less than 0.2. The spatial pattern of seasonal NDVI was in accordance with that of annual NDVI. The area where NDVI was improving was larger than where it was worsening. In general,NDVI increased gradually within the basin,but the sustainability of this trend was spatially varied. A clear and positive correlation existed between NDVI and precipitation and the determination coefficient was 0.496. The NDVI rate of increase with precipitation was 0.052/100mm. Annual average NDVI was near 0.7 in areas with annual precipitation over 1000 mm,and dropped to 0.155 when annual precipitation was less than 400 mm. The negative correlation between NDVI and elevation was evident with a determination coefficient of 0.574. The NDVI rate of decrease with elevation was about-0.016/100m. When the elevation was below 2000 m,average annual NDVI was 0.8.