| The net primary production of vegetation (NPP) is a key parameter and indicator for us to research many kinds of ecological processes of ecosystem as well as human-natural system sustainable development and effective utilization. This paper mainly uses the meteorological data and SPOT/VEGETATION NDVI data of Heihe River Basin from1999to2010, and the modified CAS A model to simulate the net primary production of vegetation in Heihe River Basin. The spatial-temporal characteristics of related factors of NPP and the NPP in subregions of Heihe basin and different vegetation types have been profoundly analyzed. The results are as follows:(1) The climate change shows the trend of warming and wetting during the period from1961to2010in Heihe River Basin, the annual average temperature is4.7℃and the precipitation is192mm; the increasing trend of annual average temperature and annual total precipitation is0.37℃and6.03mm per ten years. The spatial distributions of annual average temperature are decreasing from northeast to southwest and annual precipitation is increasing from north to south; the tendency of annual average temperature is decreasing from northeast to southwest and the annual precipitation is increasing from north to south. The spatial distribution characteristics of annual total radiation of Heihe Basin is decreasing from north to south; the maximum value of annual total radiation is located at the northern area of Ejina and the minimum value is located in Jiuquan and the southeast areas of Heihe Basin. The annual total solar radiationof the entire basin has increased in nearly12years, the highest added value is17.28MJ/m2, the minimum value is2.95MJ/m2.(2) The vegetation coverage is not high overall in Heihe River Basin, which gradually changes with the trend of desertification from the southeast to the northwest; the vegetation types in the basin is less and coverage areas are smaller; the present vegetation coverage shows the ribbon change trend of "reducing-remains the same increasing-reducing " from south to north of Heihe River Basin from1999to2010; the vegetation coverage level of the seasons in the year gradually improved except winter, the improved area is38081.12km2, accounting for26.65%of the total area; Because of the climate and human factors affect together, it’s found that there are still vegetation coverage degenerations in the middle and upstream area of the Basin, which covers an area of2233.83km2.(3) Verification analysis shows that the modified CASA model is suitable for the simulation of NPP in Heihe River Basin. The analysis finds that the total NPP amount of the Heihe River Basin present an increasing trend in volatility, which increased by31011gC/yr. The annual NPP value of the entire basin changes between0.19and601.09gC/m2.NPP in the upstream region is increasing with the trend of3.5gC/m2/yr, and the multi-year mean value is157.62gC/m2. NPP in the middle region has increased in volatility, with the trend of2.06gC/m2/yr, the multi-year mean value is57.92gC/m2. The increasing trend of NPP in downstream of the basin is0.31gC/m2/yr, the multi-year mean value is10.55gC/m2.(4) In recent12a, the NPP in January and February of Heihe River Basin both has a weak decreasing trend, the average change value is between-0.01and-0.02gC/m2/yr, the rest of the year show an increasing trend, especially in June, July, August and September, the NPP have increased greatly. In the all seasons, vegetation NPP in summer and autumn is the largest. NPP distribution in Heihe River Basin is generally more in the south than in the north, and it’s more on both sides of the river and Oasis than other regions; the total production of NPP in the upstream area is the largest, but its volatility is greater than the region in middle and downstream areas whose total NPP production is less than the upstream area.(5) Compared with1999, NPP production capacity of the ten vegetation types all have an increasing trend, average increased value is21.02gC/m2, the increase of NPP in Heihe River Basin has great significance to the sustainable and healthy development of the regional ecosystem. The increase of swamp vegetation NPP is46.24gC/m2, which is the greatest in the all vegetation types; The NPP increase of the cultivated vegetation, grassland and meadow is the second, followed by39.22gC/m2,32.49gC/m2and27.63gC/m2. The total NPP of the grassland ecological system in Heihe river basin is the most, which has an important significance to the basin ecological environment.(6) The average annual accumulated NPP production in Heihe River Basin is negatively correlated with the annual average temperature and total annual amount of solar radiation, but positively correlated with total annual precipitation, so moisture is the limiting factor of NPP in Heihe River Basin. The average annual accumulated NPP production in the upstream area is positively correlated with the total annual amount of solar radiation and annual total precipitation, but negatively correlated with the annual average temperature; The average accumulated NPP production in the middle region is negatively correlated with the annual average temperature and weakly negatively correlated with total annual amount of solar radiation, and positively correlated with total annual precipitation. The average annual accumulated NPP production in the downstream area is positively correlated with the annual average temperature, and negatively correlated with annual total precipitation, but it has no significant correlation with the total annual amount of solar radiation. |
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