Vegetation Changes and Their Causes in the Yellow River Basin under the Background of Climate Change

Understanding the spatiotemporal variations of vegetation in the Yellow River basin and their influencing factors is important to formulate policies for the construction of ecological civilization. Based on the MODIS (Moderate Resolution Imaging Spectroradiometer) vegetation index (normalized difference vegetation index, NDVI) data and meteorological observations from 2001 to 2020, this study investigates the spatiotemporal evolution characteristics and driving factors of vegetation through the mean method, unary linear regression, partial correlation analysis, and multivariate residual trend analysis. The results show that the increased NDVI dominates most of the Yellow River basin but with large spatiotemporal variability. In particular, the largest increased NDVI approaches to 0.0496 per 10 years in the middle reaches of the Yellow River basin. In the growing season, areas with significantly positive NDVI increase mainly in the western and southeastern of the Yellow River basin, most evidently in irrigated areas along the Ningxia and Hetao Plain. Both precipitation and temperature play an important role in the NDVI changes for most areas of the Yellow River basin. For the Yellow River basin as a whole, contributions from the precipitation and temperature to the NDVI change approach to 32.6% and 15.9%, respectively. Contributions from the precipitation are mainly found in the upper reaches (50.7%), while those from the temperature are mainly seen in the lower reaches (32.3%). On the other hand, human activities and climate change can account for 78% and 22% of the NDVI changes in the Yellow River basin, respectively. In particular, contributions from human activities are more than 80% in the central region of the Loess Plateau. Meanwhile, the drought is also a key driver to cause the increased NDVI changes in the Loess Plateau in central Gansu and the Hedong sand area (with a correlation of 0.6), which is especially higher in the upper reaches of the Yellow River basin.