China’s deserts greening and response to climate variability and human activities

Impact of human activities The impact of human activities was calculated by residual analysis. Areas where human activi- ties caused NDVI variations were greater than climate variability were classified as human activities impact areas. Fig 7 shows the region where NDVI variations were caused by human activities, where considerable greening trends were observed. This region included the south- ern part of the Gurbantunggut Desert, the edge of the Taklimakan Desert, and the Kubuqi Desert. To further identify which human activities caused the deserts greening, we compared Land- sat images and Google Earth images of the desert greening areas with those of the desert non- greening areas. The images for 2000 and 2017 indicate that land cover changes can be clearly observed. By comparison, there were two main types of human activities that caused deserts greening: oasis expansion and sand stabilization measures. Specifically, the areas showed greening trends in the southern part of the Gurbantunggut Desert, the northwestern edge of the Taklimakan Desert, the eastern Kumtag Desert, the Badain Jaran Desert, and the Tengger Desert were transformed into cropland due to the expansion of oasis. The greening areas in the Kubuqi Desert changed into shrubs and grass grids due to sand stabilization measures. Due to the space limitation, only a few image comparisons before and after the greening of the deserts caused by human activities are shown in Fig 7. More remote sensing image evidence

Fig 6. Spatial distribution of the Pearson correlation coefficient for the relationships between the NDVI and climatic factors. (a) Correlation between the monthly NDVI and temperature. (b) Correlation between the monthly NDVI and precipitation. (c) Correlation between the annual NDVI and temperature. (d) Correlation between the annual NDVI and precipitation. https://doi.org/10.1371/journal.pone.0256462.g006 PLOS ONE China’s deserts greening and response to climate variability and human activities PLOS ONE | https://doi.org/10.1371/journal.pone.0256462 August 30, 2021 12 / 20