Three decadal changes of vegetation cover and phenology over the arid and semi-arid regions in China
The arid and semi-arid regions in China cover nearly half of the national land area and are subjected to significant climate warming and intensive human activities. Concerns arise from the effects of the climate change and anthropogenic disturbance on vegetation dynamics in the arid and semi-arid regions. In this study, we used remote sensing dataset of vegetation index (GIMMS NDVI3g, 1982-2011) and corresponding climate and social economic dataset to (1) illustrate changes in the vegetation cover in the last three decades, (2) detect the interannual variations of the spring phenology using the fixed threshold method, ratio methods, and the curve fitting method and (3) analyze the driving effects of the climate change and anthropogenic disturbances on the vegetation change in the arid and semi-arid regions in China.
Vegetation cover generally has increased mostly occurring in the semi-arid regions. Specifically, NDVI increased in grasslands and croplands but there was no trend for the desert vegetation. Steppe NDVI increased in spring but decreased in summer especially in the Inner Mongolian plateau. Three methods were applied to recognize the growing seasons and the threshold method showed the most reasonable results. Spring phenology advanced in steppe vegetation in the Inner Mongolian plateau while it was delayed in the Qinghai-Tibet Plateau. Annual variations of precipitation in spring and summer had significant contribution to the NDVI variation, especially in the desert vegetation. Although no significant relationship was found between annual mean temperature and NDVI, green-up date was preceded due to spring warming in steppe and meadow vegetation. The enhancement of residential density showed significant correlation with the area of increased NDVI in Xinjiang and Gansu province, while an adverse relationship was found in Qinghai-Tibet Plateau because of overgrazing. Our results highlight a combined role of climate change and regional human activities in the control of vegetation dynamics in the arid and semi-arid regions in China.