Abstract
Abstract. Quantification of vegetation change and its coupling relationship with climate change has become the central topic in current global change researches. The Normalized Difference Vegetation Index (NDVI) time series data and meteorological data from 1998 to 2016 were collected to investigate the temporal and spatial variations of NDVI in growing season in the Yellow River source region and its response to climate change, based on the trend analysis, Mann-Kendall test and correlation analysis．The results indicated that: (1) In the past 19 years, the average NDVI in the region showed a slow increase, with a growth rate of 0.002/a and a catastrophe point in 2005, and the area with an upward trend accounted for 71.4% of the total area. (2) The climate of the area had been becoming warm and moist since the recent 19 years, both precipitation and temperature in growing season showed an upward trend. The partial correlation analysis showed that NDVI was positively correlated with precipitation and temperature, significantly relevant area accounting for 31.01% and 56.40% of the total area individually. The sensitivity of NDVI to temperature was higher than that of precipitation. According to residual analysis over the 19 years, human activities had negative effects on NDVI accounting 53.58% of the study area, and the implementation of a series of ecological protection engineering measures was the main cause leading to an increasing trend of NDVI after 2005.
Highlights
The global environmental change marked by "global warming" and its possible serious impacts on the ecosystems have attracted great attention of scientists around the world (Walther, 2002)
In the context of global climate change, it is of great significance to master the spatiotemporal variation of vegetation cover to regulate ecological processes and ensure ecological security
The study on vegetation cover in China from 1982 to 1999 using GIMMS Normalized Difference Vegetation Index (NDVI) data showed that 86.2% of China's area was an increasing trend, and the changes in vegetation NDVI were significantly affected by climate fluctuations and had obvious regional differences (Piao, 2001)
Summary
The global environmental change marked by "global warming" and its possible serious impacts on the ecosystems have attracted great attention of scientists around the world (Walther, 2002). Its time series can intuitively reflect the vegetation growth and coverage status(Zhang, 2014), and has been widely used in global and regional vegetation change research. The study on vegetation cover in China from 1982 to 1999 using GIMMS NDVI data showed that 86.2% of China's area was an increasing trend, and the changes in vegetation NDVI were significantly affected by climate fluctuations and had obvious regional differences (Piao, 2001). Many scholars (Xu,2007; Chen,2010; Zhang,2018) have research much about the vegetation changes in more regions of China. These studies show that vegetation coverage in different regions was increasing, and ecosystem of Qinghai-Tibet Plateau is very fragile, more sensitive and rapid response to climate change
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