2001-2010年疏勒河流域植被净初级生产力时空变化及其与气候因子的关系

通过改进的光能利用率CASA模型估算2001-2010年间疏勒河流域陆地生态系统的净第一性生产力（NPP）,采用线性趋势分析、变异系数和Hurst指数等方法,分析了NPP的时空变化特征及其与气候因子的相关性。结果表明：①疏勒河流域NPP的空间分布具有明显差异,空间上呈现西北低、东南高的趋势,且具有较明显的经向"条带"分布特征,2001-2010年,NPP平均值为102.26 gC m^-2 a^-1。②2001-2010年,疏勒河流域NPP总体呈增长趋势,年际波动较大,NPP明显增加的区域占总面积25.15%,明显减小的区域约占11.93%。③Hurst指数分析显示,疏勒河流域NPP变化的同向特征强于反向特征,其中持续改善地区占总面积的78.3%,21.7%的区域将由改善转为退化。④在年尺度上,降水是植被NPP变化的主要影响因素,NPP与降水呈弱的正相关关系,与温度相关性不显著;在月尺度上,温度是NPP变化的主要控制因子。疏勒河流域NPP对气候因子不存在明显的时滞和累积效应。

Spatio-temporal variation in vegetation net primary productivity and its relationship with climatic factors in the Shule River basin from 2001 to 2010

Vegetation net primary productivity (NPP) is the solar energy fixed by vegetation during photosynthesis, which can be described as the net increase in biomass per unit time per unit area. The NPP, which plays an important part in the terrestrial carbon cycle, directly reflects the production capacity of terrestrial vegetation under natural conditions, and determines the ability of ecosystems to store carbon. The Shule River basin, located in northwest Gansu Province, is an important water source and ecological division within the Hexi Corridor. Increasing human populations and regional economic development have resulted in severe environmental problems within the study area, including natural disasters, vegetation degradation, and soil erosion. The study of NPP in the Shule River basin can provide a scientific basis not only for the prevention and control of natural disasters but also for the improvement of the ecological environment. This is important for local sustainable ecological development in the context of global climate change. The NPP in the Shule River basin was calculated using Moderate Resolution Imaging Spectroradiometer (MODIS) images, meteorological data, and vegetation type maps, along with an improved Carnegie-Ames-Stanford Approach (CASA) NPP model. The spatio-temporal characteristics of NPP in the Shule River basin were analyzed for the period 2001-2010, using linear trend analysis, the coefficient of variation, and the Hurst index. The relationship between NPP and climatic factors was investigated. The results showed that: (1) NPP in the Shule River basin had considerable regional differences. NPP gradually decreased from southeast to northwest in the Shule River basin, and presented a noticeable linear pattern in a longitudinal direction. The inter-annual variability showed overall growth from 2001 to 2010. The annual NPP value ranged from 99.97 to 127.2 gC m^-2 a^-1, with the minimum value occurring in 2001 and the maximum in 2010. The average annual NPP was 125.08 gC m^-2 a^-1 over the period 2001-2010; (2) however, within this overall increase, the annual NPP across the Shule River basin varied from 2001 to 2010. Of the total area of the basin, 25.15% showed a significant increase in NPP, whereas 11.93% showed a significant decrease; (3) the Hurst index analysis indicated that the majority of changes in NPP followed the same direction; 78.3% of the entire study area was predicted to follow a continuously increasing trend, while 21.7% of the total area will decrease in future; and (4) there was a weak relationship between NPP and annual precipitation, and no significant relationship between NPP and average temperature at an annual scale, indicating that precipitation was the key influencing factor. However, at a monthly scale, temperature was the dominant climatic factor affecting NPP in the study region. Analysis of the relationships between NPP, precipitation, and temperature showed that correlations at an annual scale were lower than those at a monthly scale. Precipitation and temperature exerted a variety of influences on different parts of vegetation NPP. The relationship between NPP and climatic factors suggested that NPP displayed no obvious time lag or cumulative effect due to climatic factors.