| The Loess Plateau is a region with the most serious soil erosion in the world.It has a harsh ecological environment and poor natural geographical conditions.In order to improve the ecological environment of the Loess Plateau,the state initiated and implemented the Grain for Green Program in 1999.Since the implementation of this project,the vegetation coverage of the Loess Plateau has been greatly improved.But such a large-scale vegetation restoration is bound to have an impact on the terrestrial water storage of this region.However,the existing research is limited by data collection and local computer performance,which result the study sequence of the vegetation coverage is short and the spatial resolution is low.In addition,the change of water storage on the Loess Plateau has been considered mostly from the point scale,which lacks the research on the regional scale.In order to analyze the dynamic change of the vegetation coverage on the Loess Plateau and to explore its impact on water storage from the regional scale since the implementation of the Grain for Green Program,this paper has used Landsat Surface Reflectance data to monitor the spatial distribution and spatial-temporal dynamic change of the vegetation coverage on the Loess Plateau from 1987 to 2015 based on Google Earth Engine.Then,combined with meteorological data,land use types data,and socio-economic data,the effects of climate change and human activities on the vegetation coverage on the Loess Plateau were analyzed.Finally,using the GRACE gravity satellite data and the Global Land Data Assimilation System from 2003 to 2015,we have studied the response of water storage to vegetation coverage change on the Loess Plateau.The main results are as follows:(1)The annual vegetation coverage significantly increased from 41.78%in 1987 to53.23%in 2015(P<0.05),especially after the implementation of the Grain for Green Program(2000?2015)with a significant increase of 0.59%/a(P<0.05).However,no significant change was observed for the vegetation coverage during 1987?1999(P>0.05).At a pixel scale,about 72.93%of the research area showed an increasing vegetation coverage and 38.31%of the research area had a significant increase in vegetation coverage(P<0.05).(2)Vegetation coverage change was affected by both climate and human factors.Taking 1987?1999 as reference period,the relative contributions of climate change and human activities to vegetation coverage change were 23.77%and 76.23%during2000?2015,respectively.Therefore,human activities were the dominant factors for vegetation coverage change on the Loess Plateau.The Grain for Green Program has greatly improved the vegetation status on the Loess Plateau,but the expansion of city has caused significant degradation of vegetation coverage in some areas.(3)The terrestrial water storage decreased significantly(P<0.05)by a rate of-6.31mm/a during 2003?2015 and the annual reduction of the terrestrial water storage was about3.94*10~9 m~3.From the spatial analysis,the terrestrial water storage in most area of the Loess Plateau was decreasing,and the decrease degree in the eastern region was higher than that in the western region.The deep-water storage was the main reduction of the terrestrial water storage.As one of the components of the deep-water storage,groundwater was stable during 2003?2015,and had little impact on the change of the deep-water storage.The implementation of the Grain for Green Program caused excessive consumption of deep soil moisture,which was the main reason for the decrease of the deep-water storage on the Loess Plateau. |
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