Estimation Of Net Primary Productivity Of Vegetation In Huaihe River Basin Based On CASA Model

Net Primary Productivity of vegetation(NPP,Net Primary Productivity)is one of the important research contents of environmental ecology,an important indicator of life activities and energy conversion of vegetation,and a major factor for determining carbon source,carbon sink and regulating ecological process of ecosystem.Huaihe River Basin is an important base of grain production,energy and mineral resources and manufacturing industry.The ground level is flat and open,and the alluvial plain and floodplain at low altitude and low altitude are widely distributed.The climate is a transitional zone between north and south,mild and humid.Henan province occupies the largest area in the basin,followed by Anhui,Jiangsu,Shandong and Hubei provinces,which flow through about40 cities.Both economic growth and population growth are at a relatively fast level.Based on the CASA(Carnegie Ames-Stanford Approach)model,the use of NDVI and land cover,RS/GIS data and meteorological data,such as temperature,evaporation is the Huaihe River Basin in the study area of vegetation NPP estimate in 2007-2016,and carefully to the Huaihe River and watershed partition spatial distribution of vegetation NPP,time changing and change trend are analyzed,in order for the Huaihe River Basin ecosystem research,the carbon cycle and ecological restoration,environmental protection,etc.To provide reference and reference.Based on the results of model analysis,it is found that:(1)from the perspective of spatial distribution,the spatial heterogeneity of vegetation NPP in Huaihe River Basin is obvious.The maximum value of vegetation NPP is 965.17g C/m~2,and the average annual value is 332.57g C/m~2,decreasing from southwest to northeast.The distribution of NPP was different in subregions.In the secondary subdivision,the average annual NPP of the upper reaches of Huaihe River is 367.39g C/m~2,the highest value from west to south,and the second highest value from northeast.The middle reaches of The Huahei River are345.29g C/m~2,and a small part of the south and west have high values concentrated.The NPP in the eastern Hongze Lake is low,and the NPP gradually decreases from the central to the south and west.The lower reaches of Huaihe River are 331.53g C/m~2,high in the west and low in the east.Yi Shusihe District is 298.66g C/m~2,with high in the south and low in the north and low in the west and low in the east.The vegetation NPP of each region in the three-level subregion is in descending order:the South Bank of Wangbanglan Interval,the South Bank of Wangjiaba Interval,the North Bank of Wangjiaba Interval,the North Bank of Lixia River Interval,the North Bank of Xianbanghong Interval,the South Bank of Bangbanghong Interval,the West Bank of Nansihu,Gaotian District,Yi Shuhe District,Zhongyunhe District,Rigan District and the East Side of Nansihu.(2)From the perspective of time scale,vegetation NPP in the Huaihe River Basin showed a wavy rising trend from 2007 to 2016,a slow decline from 2008 to 2011 and from 2013 to 2015,and a rapid increase in 2012 and 2016.The change of sub-region is basically consistent with that of Huaihe River Basin year by year and presents an upward trend.In each month of the year,vegetation NPP first increased and then decreased,concentrated from May to September.In July,the highest vegetation NPP was 64.63g C/m~2,making the largest contribution to the annual vegetation NPP,accounting for nearly one-fifth of the annual proportion.In February,the lowest vegetation NPP was2.63g C/m~2.In terms of seasons,it is concentrated from the end of spring to the beginning of autumn,and the highest in summer,with an average of 162.05g C/(m~2·a),followed by spring,followed by autumn,and the lowest in winter.(3)Using trend analysis method,it is found that the variation trend of Huaihe River Basin from 2007 to 2016 is an average annual growth of 14.27g C/m~2,about 89.34%of the area is an increasing trend,and 10.66%is a decreasing trend.The growth trend is in the range of 0.01—20.58 g C/m~2,accounting for about 71.41%.The growth trend of Huaihe River Basin is higher in the south and lower in the north,while it is more obvious in the south,southwest and western mountain areas.The average monthly change trend of each month was about 1.19 g C/m~2annual growth,which showed a downward trend only in November and an increasing trend in the rest months,among which the growth trend was the highest in July and August and the weakest in December.The summer trend was strongest,followed by spring,followed by autumn and followed by winter.(4)Impacts of precipitation and temperature on vegetation NPP:There is a significant climate difference in the Huaihe River Basin.The average precipitation from2007 to 2016 is 881.38mm,and the variation trend is-3.39 mm/a.74.65%of the region shows a decreasing trend,while 25.35%shows an increasing trend.The perennial average temperature was 15.08℃,and the variation trend was 0.02℃/a.17.56%of the regional temperature changes showed a decreasing trend,while 82.44%showed an increasing trend.The average partial correlation between vegetation NPP and precipitation was-0.1933,and the negative correlation was closely related to the special plum rain weather in the Huaihe River basin and the rainstorm caused by vortex shear and typhoon.The area of positive and negative correlation is 22.50%and 77.50%of the Huaihe River Basin respectively,and the average temperature partial correlation coefficient is-0.0781.The area of positive and negative correlation occupies 41.24%and 58.76%of the Huaihe River Basin respectively.Most areas are moderately and weakly correlated.The relationship with precipitation is stronger than that with temperature.According to the research findings of this paper,CASA model has been well applied in the NPP estimation of vegetation in the Huaihe River Basin,and the model has good applicability and systematicity.Through the analysis and discussion of the temporal and spatial pattern and change of vegetation NPP in the Huaihe River basin,it can provide reference for the management of the Huaihe River Basin,and provide theoretical basis and decision-making reference for promoting the stability and smoothness of the ecosystem,ecological restoration,environmental protection and green development in the Huaihe River Basin.