| The Yellow River is the mother river of the Chinese nation and the cradle of Chinese civilization.As an important ecological barrier in China,ecological protection and highquality development in the Yellow River Basin have risen to a major national strategy.Vegetation construction is one of the important contents of ecological restoration.It is of great significance to understand the changes and driving factors of vegetation cover in the Yellow River basin in recent decades for the further development of vegetation protection and ecological construction in this area.Data used in this paper including GIMMS NDVI data with 8km spatial resolution of the upper and middle reaches of the Yellow River basin from 1982 to 2015,CRU TS4.02 meteorological dataset,vegetation type data and land use data.The methods used in this paper main including trend analysis,normalized multiple linear regression analysis and NDVI residual trend analysis.In order to provide scientific basis and theoretical reference for the ecological environment protection,restoration,construction,optimization and efficient management in the upper and middle reaches of the Yellow River basin,we analyzed the characteristics of vegetation cover changes in the upper and middle reaches of the Yellow River Basin from 1982 to 2015,and also analyzed the effects of climatic and non-climatic factors on the changes in vegetation cover during the growing season.The conclusions of this paper mainly include:Firstly,we studied the changes in vegetation cover in the upper and middle reaches of the Yellow River Basin.The research results showed that the consistency of changes in the time series vegetation GIMMS NDVI and MODIS NDVI data show high coincidence and strong consistency,and GIMMS NDVI data can be used to study vegetation cover changes and impact factors in the upper and middle reaches of the Yellow River basin over a long period of time.The temporal change characteristics showed that the growth rate of growing season NDVI showed a significant positive growth trend at 0.009/10a(P < 0.001),while the growth rate of NDVI in the upstream and middle reaches was 0.005/10a(P < 0.01)and 0.019/10a(P < 0.001),respectively.The growth rate of vegetation cover in the middle reaches was better than that in the upstream.The vegetation cover showed a significant positive growth trend in different seasons.The vegetation coverage in most areas showed an increasing trend.The areas with significantly increased vegetation cover were mainly distributed in Longzhong and Longdong Loess Plateau,Ningxia Plain,Ordos Plateau,Northern Shaanxi Plateau,Taihang Mountain and Lvliang Mountain.The areas with significantly decreased vegetation cover accounted for a relatively small area,only scattered.The change of vegetation cover in the study area was mainly in a stable state,and the vegetation growth was mainly in a stable increase.The areas with stable and significantly increased vegetation cover were mainly distributed in the northwest side of the study area and in Shanxi Province.The areas with stable and significantly decreased vegetation cover were only scattered.The future vegetation cover changes will show a strong sustainability,and the growing season NDVI change in 24.84% regional will show a continuous improvement trend,mainly distributed in the Loess Plateau of the Yellow River Basin.The growing season NDVI change in 6.34% regional will show a degrading trend,mainly distributed in Gansu,Ningxia,Inner Mongolia and Shanxi,scattered in Longzhong Loess Plateau,Ningxia Plain,Ordos Plateau and Taihang Mountain,and we need to further strengthen supervision in the future.Secondly,we studied the effects of climate factors on changes in vegetation cover in the upper and middle reaches of the Yellow River Basin.From 1982 to 2015,the temperature fluctuation in the growing season increased significantly.However,the proportion of precipitation and cloud cover increased but did not change significantly.The influence of single climatic factor on vegetation growth showed that temperature and precipitation can promote vegetation growth in most areas.The areas where the temperature and NDVI were significantly positively correlated(P<0.05)were distributed in the source region of the Yellow River,Hetao Plain,Ordos Plateau,and northern Shaanxi Plateau.The areas that the temperature and NDVI were significantly negative correlated(P <0.05)mainly concentrated in the Guanzhong Plain.The areas with significant positive correlation between precipitation and NDVI(P<0.05)were mainly distributed in Longzhong and Longdong Plateau,Loess Plateau in southern Ningxia,Hetao Plain and Mu Us Sandy Land,Northern Shaanxi Plateau,and Lvliang Mountain.The areas where NDVI and precipitation were negatively correlated were distributed in the upper Yellow River source area,and rarely in Shaanxi and Shanxi Province.In 93.94% of the regions,NDVI was negatively correlated with the proportion of cloud cover,but the correlation was not significant.In most regions,vegetation growth was positively correlated with solar radiation intensity.The results of normalized multiple linear regression between NDVI and multiple climate factors showed that the regional areas with temperature as the main climatic factor affecting the significant change of vegetation cover account for the largest proportion,which were distributed in Inner Mongolia,Shaanxi,Shanxi and Gansu provinces.The regions with the leading role of precipitation were mainly distributed in the Mu Us Sandy Land,and also in Gansu,Qinghai,Shanxi and other provinces.The areas where cloud cover was the dominant climate factor were only sporadically distributed.Thirdly,we studied the effects of non-climatic factors on changes in vegetation cover in the upper and middle reaches of the Yellow River Basin.Non-climatic factors have different effects on vegetation restoration in different areas and periods in the upper and middle reaches of the Yellow River Basin.The significant restoration of vegetation in the upper reaches was mainly affected by climatic factors;the significant restoration of vegetation in the middle reaches was affected by non-climatic factors more strongly than climatic factors.The significant vegetation restoration areas dominated by non-climatic factors in the study area were mainly distributed in southeastern and eastern Gansu,central and southern Ningxia,central Shaanxi and central Shanxi.The significant vegetation restoration areas caused by both climatic and non-climatic factors were mainly distributed in central Gansu,Ningxia,southern Inner Mongolia,northern Shaanxi and northern Shanxi.The significant vegetation degradation areas dominated by non-climatic factors in the study area were mainly distributed in southern Shaanxi and also scattered in other provinces.From 1982-1990 and 2000-2015,the effect of non-climatic factors on the significant vegetation restoration was obvious,and it played a positive role in the process of significant vegetation restoration.The effect of non-climatic factors on the significant restoration of vegetation during 1990-2000 were not obvious.The area of significantly restored vegetation dominated by non-climatic factors increased significantly after 2000 in the Yellow River Source Ecological Function Reserve and the Yellow River Midstream Shelterbelt Construction Project Area.It indicated that nonclimatic factors,especially ecological engineering,played an obvious role in vegetation restoration after 2000. |
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