Spatiotemporal Distribution Of GPP In The Arctic And Its Response To Climate

In the context of rapid global climate change,the carbon cycle of terrestrial ecosystem has been seriously affected,especially for the Arctic with"amplification effect"of climate.Therefore,it is important to investigate the spatiotemporal of Gross primary productivity(GPP)and its response mechanism to climate in the Arctic.Thus,we first evaluated the accuracy of the MOD17A2H GPP product using the FLUXNET2015 dataset,then explored the spatial patterns,seasonal variations and interannual trends of GPP in the Arctic,and investigated the dependence of the spatiotemporal variations in GPP on land cover types,latitude,and elevation from 2001-2019.In addition,this study explored the response mechanism of the Arctic gross primary productivity(GPP)to different climatic factors such as temperature,precipitation,and fractional snow cover(FSC),analyzed the time lag of the impact of climate factors on GPP under different response directions.Finally,in order to detect the uncertainty of remote sensing products caused by spatiotemporal scale differences,this study taken trend detection as an example to quantify the spatiotemporal scale effects of remote sensing products with different spatiotemporal scales.The following conclusions are drawn:(1)MOD17A2H was consistent well with in situ measurements(R=0.8,RMSE=1.26 g C m^-2d^-1).Utilizing MOD17A2H to analyze the spatiotemporal distribution and interannual trend of GPP in the Arctic,it is found that the spatial variation of GPP and its interannual trends is partly related to land cover types,peaking in forests and lowest in grasslands.The interannual trend of GPP decreased as the latitude and elevation increased,except for the latitude between 62°N?66°N and elevation below 700 m.(2)Temperature has the strongest impact on GPP,FSC follows,and precipitation ranks last.When considering the time-lag effects,the influence direction of temperature and precipitation on GPP is consistent as that without considering the lag effect,and the positive response of GPP to temperature and the negative response to precipitation do not show time lag effects in most areas.Nevertheless,The response direction of GPP to snow is positive when considering the time lag,which is quite opposite to the case without considering the time lag.In addition,the response of GPP to these climate factors show dependence on temporal scales.The change of GPP on the monthly scale mainly depends on the spatial distribution of these climate factors.On the annual scale,GPP is also affected by the interannual change of these climate factors.(3)The magnitude of the spatiotemporal scale effect is related to the spatiotemporal scale of satellite datasets and their spatiotemporal scale difference.The spatial scale effect depends more on the dataset with the coarser spatial resolution,and the spatial scale effect is related to the dataset with the fine spatial resolution when the coarser spatial resolution dataset is fixed.For different temporal scales,the GPP difference between annual and 8-day is weaker than other temporal scale differences,which is inconsistent with our common sense.This study is of great significance to understand the carbon cycle of Arctic terrestrial ecosystem and its response to climate,and provides a reference for the development direction of terrestrial ecosystem carbon cycle in the future.In addition,this paper has a quantitative understanding of the uncertainty of remote sensing products caused by scale effect.