| Based on satellite remote sensing data and meteorological data, this research simulated surface solar radiation over the Tibetan Plateau in three elevation levels, with which the CASA model was drived to estimate vegetationnet primary productivity (NPP) on Tibetan Plateau from 1983 to 2012. Then the spatial-temporal variation patterns of NPP and its responses to climate factors were studied based on pixel spatial scale. The results showed:(1) The solar radiation model this research established in three elevation levels could reflect spatial distribution characteristics of surface solar radiation over the Tibetan Plateau more reasonably. This research had a higher precision in solar radiation than other related model (2) The spatial changes of NPP on the Tibetan Plateau were remarkable and they decreased from southeast toward northwest, correspond with the hydrothermal conditions and vegetation types. Vegetation productivity was conditioned by different meteorological factors in the southeastern and northwestern plateau. The dominant factor of vegetation NPP was temperature in southeast (precipitation more than 400 mm), and NPP increased dramatically with the rise of temperature, while the dominant factor was precipitation in northwest (precipitation less than 400 mm). Precipitation showed weak inhibitory effect on productivity increase in areas where precipitation was more than 900 mm. Probably because precipitation increased soil erosion to some extent, and soil erosion decreased the soil organic matter content, therefore, reduced productivity. (3) Interannual variability of NPP on Tibetan Plateau had a significant spatial difference. Vegetation NPP remained relatively stable in northwest plateau for many years. From 1983 to 1992, areas where NPP increased concentrated in the centralplateau, while areas where NPP decreased concentrated in the southeast plateau. From 1993 to 2002, most areas of the plateau showed an increase trend in NPP, while areas where NPP decreased concentrated in the eastern plateau. From 2003 to 2012,NPP showed an increase trend in the eastern and southern plateau, while NPP showed a decrease trend in the southeast plateau. (4) The total net primary productivity of Tibetan Plateau fluctuated in the range of 0.494 to 0.590 Pgc/a, with a trend of “slow increase -slow decrease -rapid increase”. This research showed that the increase of annual mean temperature had a significantly positive effect on the vegetation net primary productivity(R2=0.456, P<0.001). |
