Spatio-temporal Dynamic Of The NDVI And NPP In The Liaohe River Basin,China

The impact of global change on terrestrial ecosystem is gradually deepening.Vegetation is the center of material circulation and energy exchange in terrestrial ecosystem.The NDVI and NPP can reflect the vegetation dynamics with varying degrees in terrestrial ecosystem.The factors that affect the change of vegetation growth are various and complex,among which climate change and anthropogenic activities are the key driving factors.The Liaohe River Basin(LRB)is an important part of ecological security in China.In recent decades,driven by a series of ecological restoration projects,the ecological environment in the LRB has been greatly affected by climate change and human activities.Yet,how the driving factors contribute quantitatively to vegetation dynamics is not well carried out.Under the background of global warming,quantitatively distinguish the impacts of various driving factors on vegetation dynamics in the LRB is of great significance for ecological environment construction,especially in areas with weak ecosystem stability.Here we based on MODIS-NDVI remote sensing data with a resolution of 250 m × 250 m and meteorological data in the same period from 2000 to 2018,the net primary productivity(NPP)of vegetation in the LRB was simulated by CASA model.Meanwhile,we investigated spatiotemporal variability of vegetation coverage in terms of the NDVI and NPP and analyzed he effects of main climatic factors(temperature,precipitation and sunshine hours)on the change of vegetation parameters.Further analysis quantifies the contributions of climatic change and humaninduced to vegetation dynamics variations utilizing a partial derivatives analysis.The following conclusion are obtained.(1)The NDVI had a slow upward trend,and the spatial distribution decreased from east to west.In the change trend,46.51% of the area vegetation cover has been improved,36.99% of the area vegetation cover has not changed.(2)The NPP had an upward trend in fluctuation change,and spatial distribution is characterized by "high margin and low middle".In the future trend change,vegetation parameters are weak and reverse persistent.In the fluctuation degree,the variation degree of vegetation parameters tends to be relatively stable,and the fluctuation is not large.On the whole,the growth status of vegetation in LRB is relatively good.(3)The average contribution of temperature,precipitation,and solar radiation to the NDVI interannual changes over the entire region are 0.00142/a,0.00014/a,-0.00008/a,respectively.Compared with human activities,climate variability was the dominant factor to affect vegetation activities since their impacts respectively account for 69.81% and 30.19%,among which precipitation was the main climate factor.Human activities,especially ecological afforestation projects,were of great importance to vegetation growth.However,urbanization have destroyed the growth space of vegetation,which has caused a negative effect on vegetation activities.Results of this study will provide scientific support for the vegetation status monitoring in the LRB,and have practical implications for government policy in the vegetation area.