Study On Correlation Between Net Primary Productivity Of Grassland And Climatic Factors In Xinjiang Based On Improved CASA Model

The Xinjiang Uygur Autonomous Region is located in the northwest of China,the central region of the Asia-Europe continental plate.Geographical area is vast,different landforms gave birth to different types of grassland.Xinjiang grassland have variety type of grass,including natural grassland distributed all over the region,which is the more important pastoral areas in China.Grassland is a major part of the terrestrial ecosystem and has a decisive impact on maintaining ecological balance,climate and environmental change.As the most important producer of grassland ecosystem,grassland is an important factor in regulating carbon saving and ecological processes.It is significance to understand and explore the climate change and carbon cycle in arid area of northwest China that study of the dynamic changes of NPP in Xinjiang grassland.According to the production unit and the project collaboration unit the Grassland master station in the autonomous region reflection that the introduction of the ministry of agriculture recommended a province of grassland estimation model and some other recommended models,which can't meet the Xinjiang arid area grassland NPP estimation accuracy requirements,and the actual measured value deviation.Therefore,it is necessary to consider the characteristics of regional grassland resources,adopt appropriate models for different regional scales,select the appropriate parameters,and then estimate the NPP accurately.Based on the data of MOD13A1 datasets and weather stations in Xinjiang form July 2000 to July 2014,the data of precipitations and radiation combined with grassland type,biomass measured data,DEM and so on.Through the optimization of meteorological data interpolation and the localization of CASA model parameters to improve the accuracy of NPP in Xinjiang grassland.Analysis of temporal and spatial distribution of NPP.Correlation between NPP and meteorological factors in Xinjiang grassland.This paper explores the driving effect of climate on the net primary productivity of grassland vegetation in Xinjiang,with a view to assessing grassland growth and rational use of grassland resources.The main conclusions of this paper are as follows:(1)Optimize meteorological interpolationUsing different interpolation methods,estimation of NPP in Xinjiang grassland based on CASA model.Combined with measured biomass data to evaluate the results of the three interpolation methods,the study show that the interpolation results of precipitations and temperature data,which based on the ANUSPLIN method is more reliable than other methods.(MAEp =6.45,RMSEp =8.77,MAEt =2.11,RMSEt =3.52)Different interpolation methods get different results of the NPP estimates,the correlation between the measured data and the simulated values of CASA model show that the accuracy of NPP estimation based on ANUSPLIN method is the highest than others(R2 =0.7947).NPP measured values have a good linear relationship with the simulated values,which is 13.23%higher than that of Corkiging interpolation and 20.13%higher than IDW interpolation.(2)Modification of parameters in the CASA modelThis paper based on the experiment of Zhu Wenquan simulating the ?_max of typical vegetation in China,combined with the measured biomass data of field and the main grassland types in Xinjiang to get the ?_max of different grassland vegetation types in Xinjiang.Comparing the field measurement data and other research results with the simulated values of CASA model has a good effect,(R2 =0.8379)which can estimate the grassland NPP in Xinjiang.(3)Temporal and spatial changes of NPP in Xinjiang grasslandFrom the space,the distribution characteristics of grassland NPP in Xinjiang from 2000 to 2014 are north high south low,west high east low.Among them,NPP is the highest in the Yili prefecture of western Tianshan Mountains,followed by NPP of Shihezi grassland,the lower areas of NPP in Xinjiang are basically distributed in southern and eastern of Xinjiang.There are also large differences in the NPP of the grassland type,which is generally reflected as Meadow>Alpine and sub-alpine meadow>Plain grassland>Alpine subalpine meadow>Desert grasslands.From the time scale,Xinjiang NPP has a certain fluctuation change from 2000 to 2014,and there is a slight downward trend,respectively,in 2005 and 2009 to 43.856 g C/(m2·a),41.898 g C/(m2·a).Different types of grassland have different variations,among them,meadow,plain grassland are fluctuation grows,Alpine and sub-alpine meadow,Alpine subalpine meadow,Desert grasslands showing a decreasing trend.(4)The effects of climatic factors on grassland NPPThere was a significant positive correlation between NPP and precipitation in Xinjiang grassland,and it was low correlation with temperature,indicating that precipitation is an important meteorological factor affecting vegetation NPP in this area.The correlation coefficient of different grassland types is different,but all grassland types have the highest correlation with precipitation and temperature data,which indicates that the temporal effect of NPP on meteorological factors is not obvious.