Estimation Of Vegetation Net Primary Productivity In The Three Gorges Reservoir Region Based On The MODIS Data

With the development of economic, the greenhouse gas emissions have become increasingly prominent over the past few decades, which lots of scientists believe contribute to global warming. The world is facing massive environmental issues. There needs to be an international response to this problem. The global climate change is interrelated to the surface carbon cycle and ecosystem, and vegetation plays a crucial role in the carbon circle. Vegetation net primary productivity (NPP) is the important parameters to investigate the ecosystem, and it is also the basic factor of the surface carbon cycle.Because of the natural disasters and human negative activity, the ecosystem problem of the Three Gorges Reservoir Region has become severe. In recent years, there have been many environmental problems such as vegetation decreases, soil erosion, destruction of ecological balance and so on. These have threatened the life of local people. The reservoir is significance to the protection and sustainable development of the middle and lower reaches of Changjiang River. Carrying out research on NPP, is helpful for people to understand the overall environment condition, analyze and evaluate the reservoir status, make reasonable protection policy, and to make decision for natural environment management.In this study, the Three Gorges Reservoir Region was chosen as a sample region. Based on the CAS A model and MODIS data, a model was set up to estimate the vegetation NPP of the reservoir, which the solar radiation data, meteorological data and relative information were used as main remote sensing data input in it. Supported by ArcGIS, ENVI, ERDAS and GIS technology, the NPP of the reservoir in each type of vegetation and in different regions from March to November during 2000-2009 was estimated and compared. And the spatial pattern and the relationship between vegetation NPP and climatic conditions were also analyzed. The main involved work and conclusions of the study as follows:(1) The study outputted many CAS A model parameters, including Simple Ratio, Fraction of Photosynthetically Active Radiation Absorbed by the Canopy, Absorbed Photosynthetically Active Radiation by the vegetation, Te, Topt,Wε, E, Ep, et al. All this data were produced as public production for users. Their spatial resolution is 500 m, and the temporal resolution is per 1 month. The data covered the Three Gorges Reservoir Region from 2000 to 2009.(2) This study build an improved CASA model by revise the calculation of FPAR, the values of NDVI, SR and 8max. By comparing the results of vegetation NPP with other models, it proved that the improved CASA model high accuracy in the Three Gorges Reservoir Region scale.(3) The mean vegetation NPP in the Three Gorges Reservoir Region from March to November during 2000-2009 was between 451.77gC/m2.yr to 515.37gC/m2.yr, and the average mean value was 487.21gC/m2.yr. The total vegetation NPP was between 2.61×1013gC/yr to 2.98×1013gC/yr, and the average total value was 2.82×1013gC/yr. From 2004 to 2009, the NPP altered enormously. From 2004 to 2009, the NPP did not change much, but gradually stabilized overall. The seasonal changes of NPP were significantly, presented the characteristics of the single peak distribution. From May to September were the major months for NPP accumulate. The maximum NPP value for month appeared in July, shared 18.76% of the average NPP from March to November. There was a downward trend in the NPP after August, and slowly reduced from October to November. The minimum NPP value for month appeared in November, shared 2.58% of the average NPP from March to November.(4) Got the NPP that respectively corresponding to the different types of vegetation by mask processing the mean NPP. The mean NPP value of evergreen broad-leaved forest was the highest, about 858.19 gC/m2.yr. The second was deciduous broad-leaved forest, the mean NPP value was 630.01 gC/m2.yr. The values of mixed forest, farmland and grassland had all reached above 500 gC/m2.yr. The waters and cities were the lowest, only 178.15 gC/m2.yr and 180.1 gC/m2.yr. The NPP value of forest and farmland shared 77.41% of the total NPP in the reservoir. But the waters and cities were lower than other types. The seasonal changes of all types of vegetation NPP were significantly, presented the characteristics of the single peak distribution just as the total NPP trend.(5) The study had shown that the NPP values gradually decrease from east to west, from north to south in the reservoir. Wuxi owned highest gross NPP of 2.18 X 1012 gC/yr, which accounted for 7.74% of total vegetation NPP, while Yilin and Badong 2.13×1012 gC/yr and 1.93×1012 gC/yr, accounted for 7.56% and 6.86% of total vegetation NPP. Whereas the Yuzhong had very small NPP, the gross NPP was 8.1×109 gC/yr, which accounted for 0.03% of total vegetation NPP.(6) By analyzing the relationship between vegetation NPP and solar radiation, temperature, precipitation and NDVI, it concluded that NPP in the Three Gorges Reservoir Region is the complex result of multiple factors. But it was closely related to the temperature and precipitation. At the same time, the Three Gorges Reservoir has also been impacted by human activities. The construction of Three Gorges Project and immigration also interfere the stability of the ecosystem. After the implementation of a series of environmental protection measures, the ecological environment of the reservoir has been recovered, the ecological carrying capacity has been gradually improved.