Characteristics Of Vegetation NDVI Change In Northeast Asia And Its Response To Climate Factors

In recent years,global warming has become an important issue concerning the development of all mankind.Vegetation,as the primary producers in the ecosystem,serve as the main bridge connecting to the atmosphere,water and soil,the important material basis for the global cycle of material energy,and the indicator of global climate change.Therefore,monitoring and analysis of vegetation change is of great significance to research on global climate change and regional climate change.Northeast Asia is an important ecological defense for our country and a sensitive area of global change,research on the response relation between the change of vegetation cover and climate in which area will provide a positive guidance on the coordinated sustainable development in the middle latitudes of the northern hemisphere.In this paper,referring to VIPPHEN?EVI2 phenological data,GIMMS NDVI3g vegetation data,CRU climate data,CRU-NCEP climate data and VPD data from Wang et al.,the temporal and spatial variation of vegetation NDVI and precipitation,temperature,VPD and radiation is evaluated with trend analysis,removing linear trend from vectors,partial correlation analysis,sensitivity analysis and other methods.The spatial-temporal pattern of vegetation NDVI in Northeast Asia was assessed,the degree of influence of climate factors on NDVI changes was quantified,and the contribution of different climate factors was clarified.The main conclusions obtained are as follows:Main conclusions reached are as follows:(1)The vegetation coverage in Northeast Asia increases gradually from inland to coastal areas.During the growing season from 1982-2015,the vegetation NDVI showed a rising greening trend with fluctuations,the mean value over the years being0.63.Among others,the annual average forest NDVI is 0.67,and the annual average cropland NDVI 0.54.Vegetation greening trend shows latitudinal zonality-gradually descending from south to north.(2)The variation trend of the vegetation in Northeast Asia through the years shows significant spatial difference.Though the overall trend over the years is still vegetation greening,in the 00s,there was large-scale forest browning,and large-scale change of cropland for the better;in the 90s,however,there was a large-scale cropland browning trend.(3)Vegetation greening in Northeast Asia is mainly caused by global warming.However,the large-scale forest browning in the 00s is the result of the mitigated trend of global warming,substantially increased precipitation,and vegetation growth suppressed by excess water;the large-scale change of cropland for the better,on the other hand,is caused by climate warming and wetting.Browning of vegetation(especially cropland)in the 90s is the result of the hot and dry climate induced by decreased precipitation,rise of temperature and increase of VPD,and the affected photosynthetic rate because of stomatal closure under high VPD and water stress.(4)In 1982-2015,for every 10 mm increase in precipitation,NDVI increased by0.57×10^-4 on average;for every 1?increase in temperature,NDVI increased by1.51×10^-2 on average;for every 1 Pa increase in VPD,NDVI increased by 0.31×10^-1on average;for every 10 W/m² increase in radiation,NDVI increased by 0.22×10^-4 on average.Forest's sensitivity to temperature and VPD is higher than that of cropland,of which its sensitivity to VPD is 4.4 times that of cropland.Cropland's sensitivity to precipitation and radiation is higher than that of forest,of which its sensitivity to precipitation is 2.3 times that of forest.