## 6 Conclusions  
We assessed the dynamics of vegetation in a semi-arid region of Northwest China for the years from 2000 to 2019 through satellite remote sensing, and analyzed the interannual covariation between vegetation and three climatic factors--air temperature, precipitation, and VPD--at nine meteorological stations. The main findings of this research are: (1) herbaceous land greened up much more than forests (2.85%/year vs. 1.26%/year) in this semi-arid region; (2) the magnitudes of green-up for cropland and grasslands were very similar, suggesting that agronomic practices, such as fertilization and irrigation, might have contributed little to vegetation green-up in this semi-arid region since 2000; and (3) the interannual dynamics of vegetation at high altitudes in this region correlate little with temperature, precipitation, or VPD, suggesting that factors other than temperature and moisture control the interannual vegetation dynamics in this region. For follow-up research, it would be good to see if vegetation in other semi-arid regions exhibits similar characteristics of greening. **Supplementary Materials:** The following are available online at [[https://www.mdpi.com/article/10.3390/rs13214246/s1](https://www.mdpi.com/article/10.3390/rs13214246/s1)]([https://www.mdpi.com/article/10.3390/rs13214246/s1](https://www.mdpi.com/article/10.3390/rs13214246/s1)), Figure S1: Availability of remote sensing observations for the study. (a) Average number of months without valid NDVI in the period from 2000 to 2019. (b) Standard deviation of the number of months without valid NDVI in the period from 2000 to 2019. In regions other than the Lanzhou basin, the monthly NDVI estimates during the growing season are almost complete. Figure S2: Inter-annual covariation between growing season NDVI and temperature at the nine meteorological stations for the years from 2000 to 2016. NDVI for a meteorological station is the average of NDVI values in the 3 by 3 km square collocated with the meteorological station. One asterisk indicates the coefficient is at the 0.05 level of statistical significance, and two asterisks at the 0.01 level of statistical significance. NDVI for the nine stations all experienced positive trends, five of which were statistically significant. In comparison, one of the nine stations experienced statistically significant warming, one experienced statistically significant cooling, and the other seven stations experienced no statistically significant temperature trends. The detrended NDVI and temperature are correlated significantly at only two stations, the land cover types of which are barren land and cropland, respectively. Additionally, these significant correlations are negative. This suggests that temperature plays a minor role in vegetation inter-annual dynamics in the study region, and conversely, temperature is affected by vegetation dynamics at the inter-annual scale, probably through evapotranspiration. Figure S3: Inter-annual covariation between growing season NDVI and precipitation at the nine meteorological stations for the years from 2000 to 2016. NDVI for a meteorological station is the average of NDVI values in the 3 by 3 km square collocated with the meteorological station. One asterisk indicates the coefficient is at the 0.05 level of statistical significance, and two asterisks at the 0.01 level of statistical significance. The NDVI for the nine stations all experienced positive trends, five of which were statistically significant. In contrast, precipitation at the nine stations experienced large inter-annual variations, and hence no statistically significant trends. The detrended NDVI and precipitation are positively correlated at the nine stations, and seven of the correlation coefficients are larger than 0.5 and statistically significant. This suggests that precipitation plays a major role in the vegetation inter-annual dynamics in the study region.