Abstract:  

The relationship between fractional vegetation cover and environmental factors is one of the important contents for the study of the ecosystem in arid regions.In this paper,we analyzed the temporal and spatial variation characteristics of fractional vegetation cover from 2000 to 2015 in the Qaidam Basin,Qinghai Province,China based on MODIS-NDVI.Combined with DEM data and meteorological data of the basin,the correlation analysis,partial correlation analysis or overlay analysis between fractional vegetation cover and precipitation,temperature,sunshine duration,relative humidity,evapotranspiration,and altitude were calculated to explore the response characteristics of fractional vegetation cover to major environmental factors.The results showed that the fractional vegetation cover in the Qaidam Basin displayed a semi-annular decreasing trend from the southeast to the northwest.The overall fractional vegetation cover was below 20%.The human activities and the distribution of runoff broke the regularity of vegetation zonal distribution and thus affected fractional vegetation cover significantly.In the context of global warming,the fractional vegetation cover was increased significantly during the time period from 2000 to 2015,with most of the regions being widely distributed in the central and western and parts of the eastern mountainous region of the basin.Furthermore,the most obvious inter-annual variation occurred from 2001 to 2002.Especially the improvement trend of forest,grassland and meadow vegetation was particularly obvious.The relationship between fractional vegetation cover and different meteorological elements was different.The fractional vegetation cover was positively correlated with precipitation and relative humidity,and negatively correlated with sunshine hours and evapotranspiration.The relationship between fractional vegetation cover and temperature was not significant.Among them,the precipitation contributed the most to the fractional vegetation cover and was the major limiting factor to affect the growth of vegetation in the basin.Temperature indirectly affected fractional vegetation cover by affecting evapotranspiration,and contributed more to evapotranspiration than precipitation.Meanwhile,the influence of soil evaporation to evapotranspiration was much higher than that of vegetation transpiration.There was consistency of the spatial distribution between fractional vegetation cover and altitude,which meant that fractional vegetation cover had a good consistency with the spatial distribution of contour lines.Vegetation vertical differentiation was evident.Two peak values occurred in the areas of 2 800-2 900 m and 4 600-4 700 m respectively due to the influence of water source and temperature,while fractional vegetation cover was decreased rapidly above 4 700 m.This paper clarifies the relationship between multiple environmental factors and fractional vegetation cover,and makes clear the response characteristics of vegetation to major environmental factors under the background of global warming and drying,which has a great significance for the study of other ecological environment and climate change in arid regions.

Key words: fractional vegetation cover')">">fractional vegetation cover, inter-annual variation, environmental factor, correlation analysis