The Spatial And Temporal Distribution Pattern Of Vegetation Net Primary Productivity In Xinjiang And Its Climate And Anthropogenic Contribution

Xinjiang is an important hub of the “The Belt and Road”.With the continuous advancement of the “The Belt and Road” strategy,Xinjiang's economy has been developing rapidly.However,this has also brought pressure on ecological protection in Xinjiang,so it is imperative to strengthen the environmental protection.NPP is an important part of the surface carbon cycle process.It can not only directly reflect the productivity of vegetation in the natural state,but also measure the environmental quality of the ecosystem.Therefore,under the background of "warm and wet" in Xinjiang,it is very important to study the impact of climate change and human activities on NPP,for Xinjiang's ecological recovery and the healthy development of the environment.Based on the improved CASA model and Human impact model based on coefficient of variation,this paper used NDVI data,meteorological data and land use data during 2001 and 2018 to analyze the spatiotemporal pattern of NPP changes in Xinjiang in the past 18 years and the impact of land use changes on NPP.On this basis,the relative contribution of climate change and human activities to NPP in Xinjiang was calculated.The main findings are as follows:(1)From the perspective of temporal NPP change in Xinjiang,from 2001 to 2018,NPP generally showed a fluctuating upward trend,in which the annual mean value of NPP in grassland and cultivated land was the largest.From the perspective of the spatial NPP changes of Xinjiang,NPP generally showed a trend of decreasing from north to south and from west to east in the past 18 years.The area of NPP increased was greater than that of NPP decreased.In the past 18 years,the NPP in Xinjiang has been in a relatively stable state.In the future,it would continue to maintain an upward trend and the ecological environment would continue to improve.(2)From the perspective of changes in land use types in Xinjiang,from 2001 to2018,the area of grassland and unused land accounted for the largest proportion of land in Xinjiang,and they were also the main contributors to land use conversion.The other four types of land use,according to the area size,it was cultivated land,water area,woodland,and town in order.From the perspective of the impact of land use types in Xinjiang on NPP,compared with that of 2001,the total NPP of grassland,towns,and arable land increased in 2018,while the total NPP of forest land,waters,and unused land decreased.The unchanged land use types contributed the most to the total NPP change in Xinjiang,with a contribution rate of 60.88%.Among the changed land use types,the conversion of grassland,unused land and woodland to cultivated land was the main influencing factor of the total NPP growth,while the conversion of woodland area to grassland and water area to unused land had a negative impact on the total NPP change.(3)From the perspective of the impact of climate change on Xinjiang's NPP,from2001 to 2018,the temperature,precipitation and solar radiation in Xinjiang all showed an upward trend,and the three climatic factors were all positively correlated with NPP.From the perspective of the impact of human activities on NPP,from 2001 to 2018,the human impact on Xinjiang's NPP was mainly negative,with a positive impact of only27.45%,of which only cultivated land and swamp had a positive anthropogenic impact,and woodland,shrub,grassland,and desert were all negative.(4)From the perspective of the relative impact of climate change and human activities on NPP in Xinjiang,the contribution of human activities to the increase of NPP from 2001 to 2018 was higher than that of climate change,and the contribution ratios of human activities and climate change were 64.62% and 35.38%,respectively.In terms of NPP reduction,the reduced area of vegetation NPP in Xinjiang is smaller than the increased area,and human activities had a greater impact on the reduction of NPP.From the perspective of the impact of climate change and human activities on NPP increase in land use transfer,in the land types without transformation,except for cultivated land and water area,the contribution of climate change to NPP increase of vegetation is higher than that of human activities,In the transformation of land use types,climate change is the main factor for the increase of vegetation NPP in the transformation from grassland to town,from woodland to grassland,from water area to grassland,from water area to woodland,and from water area to unused land,in addition,human activities were the leading factor for the increase of vegetation NPP;From the perspective of the impact of climate change and human activities on NPP reduction in land use transfer,the contribution of human activities in land use transfer was much higher than that of climate change,and human activities were the main factor of NPP reduction in land use transfer.