Vegetation index is an important parameter that reflects the status of vegetation in an area. Analyzing the relationship between climatic factors and the vegetation index is helpful to fully understand the impact of climate change on vegetation. However, some conclusions on the relationship between the vegetation index and climatic factors are inconsistent across various time scales. Thus, this issue is addressed in the present study to enhance our understanding of the relationship between vegetation and climatic factors. With the use of the Normalized Difference Vegetation Index（NDVI） data of moderate resolution imaging spectroradiometer（MODIS）during the growing seasons from 2000 to 2009, the monthly climatic factors（i.e., mean air temperature, accumulated temperature above0 °C, and monthly precipitation） of three observations in the northern Tibetan Naqu were combined, and the within-growing-season and cross-growing-season correlations between the NDVI and the climatic factors were analyzed. First, we preprocessed the data. To eliminate the interference of human factors, especially the urban buildings in the near site, we obtained the NDVI values outside the radius of 25 km around the meteorological station. Second, we calculated the correlation coefficient between the NDVI and the monthly mean air temperature. Similarly, the correlation coefficient between the mean air temperature for the month ahead and NDVI was also calculated using the NDVI（4–9 months） and the monthly mean temperature series（3–8 months）. The same process is applied to the two months ahead and the other factors. Third, we calculated the correlation coefficient between the NDVI and the mean air temperature of the month. Similarly, the correlation coefficient of the mean air temperature for the month ahead and the NDVI for April was calculated using the NDVI for April and the mean air temperature for March. The same process is applied to the two months ahead and the other factors. The within-growing-season correlations between the NDVI and the temperature and precipitation factors were highly and positively significant, and the lag effects of the climatic factors on NDVI were most obvious for the one-month lag. By contrast, the inter-growing-season correlation between NDVI and precipitation was not significant, and the lag effect was much weaker than the within-growing-season lag effect. Therefore, the correlations between the NDVI and climatic factors vary between the within-growing-season and the inter-growing-season. Such a variation can be attributed to two aspects: the within-growing-season correlation fully considered the synchronization of the rainfall and temperature, whereas the inter-growing-season did not; the difference in sample sizes resulted in different results. In this paper, the relationship between NDVI and climatic factors is discussed at different time scales. Results show differences in some aspects. At present, most of the studies are based on the relationship between vegetation changes and climate factors in the growing season.The analysis of the relationship between vegetation development and climatic factors are more scientific and persuasive. In conclusion, much more attention should be paid to the different approaches to obtain the various correlations between NDVI and climatic factors. spects: the within-growing-season correlation fully considered the synchronization of the rainfall and temperature, whereas the inter-growing-season did not; the difference in sample sizes resulted in different results.

NDVI;气候因子;时间尺度;气候变化;MODIS;植被指数