Relative contributions of natural and man-made factors to vegetation cover change of environmentally sensitive and vulnerable areas of China

Vegetation in arid and semi-arid regions is extremely sensitive to climate change and human activities, and when disturbed, it is prone to irreversible degradation. However, the mechanisms of how natural and anthropogenic factors drive vegetation variations remain unclear for environmentally sensitive and vulnerable areas. To understand the relationships between vegetation variation, climate change, human activities, relief degree of the land surface, and El Nino-Southern Oscillation (ENSO), trend analysis, partial correlation analysis, residual trend (RESTREND), and wavelet coherence approach were utilized. Normalized difference vegetation index (NDVI), meteorological data, and ENSO were used as data sources to determine the spatial response of vegetation growth to climate change and human activity from 1982 to 2018. This study defined the 400 mm annual precipitation fluctuation zone in China (APFZC) for the first time, involving 15 provinces, accounting for 27.37% of China. Vegetation activity was mainly driven by precipitation, temperature, sunshine duration, and wind speed. Precipitation and temperature promoted vegetation activity, while the wind speed inhibited it. Moreover, vegetation variation exerts an obvious topographic effect and is deeply affected by ENSO. Under the influence of climate change from 1982 to 2018, the vegetation became greener in the Loess Plateau, North China Plain, Qinghai, and the border regions of Inner Mongolia and Liaoning; however, in the northeastern part of Inner Mongolia and the western part of Heilongjiang, vegetation was browning. In 1982-1998 and 1999-2018, the contribution rates of climate change to vegetation variation were 50.36% and 42.89%, respectively, and human activities were 49.64% and 57.11%, respectively. This information is crucial for alleviating climate change and for the ecological restoration of vegetation, especially in environmentally sensitive and vulnerable areas.