The Evaluation Of Vegetation NPP In The North China Plain Using Remote Sensing Data Of MODIS

Vegetation, an indispensable factor of the terrestrial ecosystem, plays an important role in global change. Vegetation Net Primary Productivity (NPP) is helpful to studying carbon cycle and carbon trend, and its sensitivity is also important to global climate. The evaluation of the vegetation NPP on a large scale by remote sensing information is useful to understand the carbon store, carbon cycle and carbon balance on the earth.Based on Geographic Information System, the vegetation NPP is evaluated by integrating multi-temporal remote sensing information, meteorologic data, and ecological information in the North China Plain. The involved work and conclusions as follows: (1) The applied NPP evaluation model is based on the theory of material—energy transformation—energy balance, and the simulation of the crop environment, biological and biochemical processes involving the photosynthesis, respiration during crop growth, development and production. The model is described as where, Pc is the gross photosynthetic rate; Rd is dark respiration rate; ( is initial photochemical efficiency; I is photosynthetical active radiation; Pmax is maximum photosynthesis efficiency; θ is the convexity; LAI is leaf area index; t is time, Ts is temperature of surface; Ta is temperature of air; a0 is parameter; Vm is the maximum catalytic capacity of Rubisco per unit leaf area. Meanwhile, the Evolution Water Difference Index (EWDI) is improved and applied, which is proved that it is feasible in spring in this area. (2) Moderate-resolution imaging spectroradiometer (MODIS) data (500 m spatial resolution) are much suitable to monitor vegetation on large scale. The Normal Difference Vegetation Index (NDVI) and Evolution Vegetation Index (EVI) are compared, and the fractional vegetation cover and EWDI are retrieved by MODIS data. Then the vegetation NPP in Spring (from March to April) is evaluated in the North China Plain by MODIS data. This shows that EVI is more suitable to monitor vegetation situation than NDVI.(3) The vegetation NPP in the North China plain in Spring is high in south and low in north. The distributions of vegetation NPP are related with climate and spatial pattern of vegetation. In the China North Plain from March to April of 2000, the maximum of vegetation NPP is 994.21 gC/m2, and the minimum is 7.80 gC/m2. (4) In the North China Plain from March to April, the correlation between vegetation NPP and solar illumination, temperature and precipitation are analyzed. The light energy is abundant, but its effect to NPP is not significant. The spatial distributions of vegetation are determined by temperature, also its effect is not significant. However, precipitation is variable largely, and its effect is significant to NPP. Thus the areas where water is short, is the areas where potential production is the largest. The proper measurements to decrease or eliminate effect of water shortage, are necessary for the agriculture activities in these areas.