| Precipitation use efficiency (PUE), a ratio between the vegetation net primary productivity (NPP) and the annual precipitation, can be regarded as a key index to reflect the ecosystem water-carbon coupling. Shiyang River Basin is one of the ecological fragile zone in china, the temporal and spatial distribution characteristics of NPP、PUE from the regional scale and analysis of the influence mode of climate factors, not only helps to have important theoretical meaning and realistic significance for the response of water-carbon cycle in the region to climate change, but also has a certain reference value in recovery vegetation and desertification governance based on the PUE in the future.In this study, by means of remote sensing and geographic information system, using the modified CASA model, the PUE and NPP value were simulated during 2000-2012 in the Shiyang River Basin, and the space-time distribution of vegetation NPP and PUE were analyzed, the relationship between vegetation NPP、PUE and climate factors were initially revealed. The following important conclusions were obtained:1) Through the analysis of climatic change characteristics, we could find that climate factors had the certain features of the temporal and spatial distribution during 2000-2012 of the Shiyang River Basin. From the annual distribution of view, the average annual temperature and annual total solar radiation showed a downward trend; while the annual precipitation showed weak increasing trend. From the spatial distribution, the warming trend of average annual temperature gradually increased from east to west, the increasing amplitude was not obvious; in the whole area, the average annual temperature has a relatively small change. The annual precipitation showed a gradually decreased trend from northeast to southwest; areas with the high average annual precipitation were the lager in the increasing amplitude. Total solar radiation showed a gradually increased trend from southeast to northwest; the whole area has a trend of decrease, and the more distribution the more decreased trend, the less distribution the less decreased trend.2) The spatial and temporal distribution of NPP and PUE in Shiyang River Basin was the long-term effect and the implications results of regional environment, climate, vegetation and human activities. The annual mean values of vegetation NPP in Shiyang River Basin reached 114.86 gC·m-2·a-1 in 2000-2012, which varied in the range between 0 and 577.1 gC·m-2·a-1; the annual mean values of vegetation PUE was 0.51 gC·m-2·mm-1, which varied in the range between 0 and 2.51 gC·m-2·mm-1. In 2000-2012, the spatial pattern of the vegetation NPP and PUE value showed gradually decreased from Northeast to southwest in Shiyang River Basin, and showed a slightly upward trend year by year. Qilian Mountain in the Southern area was the high value of NPP and PUE, the hilly area in northern area was low, central plain was somewhere in between.3) Under different vegetation types of distribution of NPP and PUE were the highest in broad-leaved forest. After contrast was found, NPP and PUE distribution in different vegetation types was similar, the annual NPP was ranked from large to small as follows:broad-leaved forest, coniferous forest, cultural vegetation, shrub, grassland, barren vegetation and desert; the annual PUE was ranked from large to small as follows: broad-leaved forest, cultural vegetation, coniferous forest, shrub, grassland, barren vegetation and desert. In order to improve the ecological degeneration of Shiyang River Basin, we could develop the forestry and cultivated vegetation types.There is a strong relationship between the vegetation of annual average NPP、PUE and the elevation, vegetation distribution of NPP and PUE with the change trend of rising altitude were increased first and then reduced. The annual average NPP and PUE achieved the highest when the altitude ranged from 3000 to 3500m; and rised with the increase of altitude under the altitude of 3000m; but,the annual average NPP and PUE had a gradually reduces with the increase of altitude above the altitude of 3500m.4) The annual average NPP has a negatively correlation with the average temperature, a highly positively correlation with annual precipitation, and a slight positive correlation with the annual total solar radiation in the most area of the basin from 2000-2012. The change of vegetation NPP was mainly influenced by temperature factor in the Qilian Mountain; and the change of vegetation NPP was mainly influenced by rainfall factor in the northern mountainous and the Central Plains. The annual average PUE was positively correlated with annual average temperature and total solar radiation in most areas of Shiyang River basin. But in the whole region, the annual average PUE and annual precipitation showed a significant negative correlation. |
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