Spatio-temporal dynamics of NDVI and its response to climate factors in the Heihe River Basin, China

Ecosystem in the Heihe River Basin (HRB) is very vulnerable and sensitive to variations in the climatic conditions and human activities. In this study, The SPOT and MODIS NDVI time series data from 1998 to 2012 were used to analyze NDVI variation characteristics and its response to climatic factors in the HRB based on Mann-Kendall test, relative Sen's slope, linear regression and partial correlation analysis. The results indicate that: (1) There is an obvious decreasing trend during 1998-2001 and a significantly increasing trend from 2001 to 2012. The vegetation in the HRB was improved by 1.5% of annual average level from 1998 to 2012, and rate of change is greatest in the lower reaches. (2) During 1998-2001, the rainfall is proved to be the most significant factor influencing NDVI for each reaches, and temperature and radiation are also related significantly with NDVI in the middle and lower reaches respectively. However, during 2001-2012, all climatic factors are not significantly related with NDVI for each reaches, excepting rainfall in the middle reaches. This demonstrates that the climatic variation cannot totally explain the significant improvement of vegetation during 2001-2012 in the HRB, whereas ecological restoration projects implemented in this period might be a reasonable factor for the improvement of ecological environment in the HRB.