Analysis Of Global NPP Spatial-temporal Variation In A Data-driven Perspective

The terrestrial ecosystem is an important carbon sink in the global carbon cycle,which can fix C02 in vegetation or soil to offset carbon emissions,providing a solution to the reduction of atmospheric C02 concentration.As an important part of the terrestrial carbon cycle,vegetation net primary productivity(NPP)represents the fixed atmospheric carbon in the vegetation,which is an important indicator for the level of the ecosystem carbon sequestration.Some studies have explored and analyzed global or regional NPP variations,when these traditional methods analyze NPP variations,they will divide the region according to geographical location,vegetation type,temperature zone,etc,and then compare the NPP variation of different areas.However,the method of regional division may introduce the prior information to the conclusion,and the results of different partitioning methods vary significantly as well.In view of the above problems,this paper uses GLOPEM AVHRR NPP during 1990-1999 and MODIS MOD17A3 NPP during 2000-2014,the support vector clustering method is used to analyze the temporal-spatial variation of global NPP from a data-driven perspective,geographic information technology and mathematical statistics method were used to compare the relationship between different NPP categories and climate types and vegetation types.The main research contents and conclusions of this article include:(1)The temporal and spatial variations characteristics of global vegetation NPP were analyzed.The global total NPP shows an increasing trend during the period from 1990 to 2014.Areas with higher levels of NPP shows increased NPP recent years.The 12 NPP variation patterns were obtained using support vector clustering method.The NPP variations in tropical low latitudes are more complex and the level of NPP is higher.SVC3 and SVC4 have higher NPP than at similar latitudes elsewhere.The NPP of the same vegetation varies in different NPP patterns affected by climate condition.(2)This paper analyzed the temporal and spatial changes of global forest NPP and the spatial malconformation of global forest carbon absorption.Under similar climatic conditions,forests with more evergreen broad-leaved trees may achieve higher NPP,and the climate difference at the same latitudes is an important factor of affecting NPP levels.In recent years,the spatial distribution malconformation of global forest carbon absorption has declined.The difference in the relative intensity changes of forest carbon absorption is more significant in tropical low latitudes and the distribution of the forest carbon absorption is imbalance,while there were fewer variation patterns in middle and high latitudes,the distribution of the forest carbon absorption is more balanced.(3)This paper analyzed the temporal malconformation and the temporal and spatial coupling changes of global forest carbon absorption.From 1990 to 2014,the absorption of forest carbon in most parts of the world shows a weakening trend,and the forest carbon absorption near the Andes was enhanced.There is a significant difference in forest carbon absorption of the tropical savanna and tropical rainforest regions,and the temporal malconformation is even more pronounced.The difference of temporal-spatial coupling changes of forest NPP is more significant from high latitudes to low latitudes.