Vegetation dynamics and the relations with climate change at multiple time scales in the Yangtze River and Yellow River Basin, China

Understanding the vegetation dynamics and their responses to natural and anthropogenic factors plays a key part in improving ecosystem structure and function in the context of global warming. In present study, the spatio-temporal heterogeneity of vegetation coverage and their relationships with climate change at different time scales in the Yangtze River and Yellow River Basin (YZYRB) were analyzed based on the Ensemble Empirical Mode Decomposition (EEMD). The results showed that the growing-season Normalized Difference Vegetation Index (GSN) increased by 0.011/decade (z = 4.09) during 1982-2015. The areas with significant improvement trend were mainly distributed in the central and eastern Yellow River Basin (YRB) and the central Yangtze River Basin (YZRB), while the east YZRB was significantly degraded. The correlation analysis based on multiple time scales illustrated that as the time scales increased, the response of vegetation to climate variations became more prominent. Especially under the long-term trend, the significance of the correlations between vegetation and precipitation/temperature increased with the area percentage increasing up to 81.5% and 93.62%, respectively. The relationship between GSN and precipitation was mainly driven by climatic conditions and vegetation types at 3-year time scale, altitude and vegetation types for the long-term trend. The relationship between GSN and temperature was mainly related to the climatic conditions and elevation at 3-year time scale, the vegetation types and climatic conditions at 6-year time scale and for the long-term trend. Multivariate regression analysis confirmed that the climate change had greater influences on vegetation than that of anthropogenic activities in 50.8% of the study area, which distributed in the central area of the YZYRB.