Analysis on Jinghe watershed vegetation dynamics and evaluation on its relation with precipitation

Vegetation degradation is one of the key subjects in the study of global environmental changes, and the Normalized Difference Vegetation Index (NDVI) is generally recognized as a good indicator of terrestrial vegetation productivity and growth status. To evaluate the vegetation dynamic changes in the Jinghe watershed on Loess plateau from 1982 to 2003, major methods of change slope, principal component analysis and correlation analysis were employed with 8 km resolution NOAA-NDVI time series data. Based on these analyses, the relationship between precipitation and NDVI was discussed. Results show that there has been little change in both amplitude and variety of NDVI during the past 22 years. Vegetation in the upper stream areas, typically the watershed marginal mountain areas, changes significantly. A trend analysis shows that the similar finding on vegetation dynamics in different areas tends to be induced by climate changes and human land use transformation. A standardized principal component analysis indicates that the first two components, PC1 and PC2, are closely related to vegetation and climate changes, while PC3 and PC4 are connected with floodwater in flooding seasons, and PC5 and PC6 reflect the effects of human activities. Finally, the correlation analysis shows that there is a close positive relationship in this region between NDVI and precipitation. The rainfall sensitivity threshold reaches 550 mm or even higher.