【摘要】 【目的】分析黄土高原砒砂岩区植被覆盖的时空动态变化特征,探讨土地利用类型对归一化植被指数（NDVI）的影响及植被盖度与水热因子的空间和时滞关系,为黄土高原砒砂岩区退化植被恢复重建和黄河粗泥沙的综合治理提供思路,改善当地生存条件和生态环境。【方法】在皇甫川流域,利用2000—2015年MODIS13Q1共192期产品,以ENVI为技术平台,计算NDVI,采用一元线性回归分析法和Spearman相关分析法分析其在不同时间尺度上的动态变化和不同空间尺度上的分布格局,基于地理空间系统分析其在不同土地利用方式下（分辨率30 m）的时空特性,并运用Spearman相关分析法详细分析NDVI和水热因子间的响应关系。【结果】2000—2015年,皇甫川流域NDVI平均值为0.429～0.630,呈线性增加趋势,增长速率为0.004 2·a^-1,生长季与非生长季差别显著,5月出现最大值,气温和降水量亦呈增加趋势,增长速率为0.034 8℃·a^-1和6.27 mm·a^-1;空间上,纳林川子流域16年来NDVI为0.1～0.3,十里长川子流域为0.25～0.4,均呈"沟道高-坡面低"的空间格局;不同土地利用类型下NDVI为0.2～0.25,表现为林地>耕地>草地>未利用地,16年的增长速率表现为草地>未利用地>林地>耕地;纳林川支流沟道附近NDVI呈下降趋势,变化率为-0.09～0,而远离沟道的坡面地区呈上升趋势,变化率为0～0.12;十里长川支流沟道附近NDVI变化率为0～0.4,而沟道周围地区变化率为0.04～0.12;整个流域内NDVI的增长趋势在空间上呈坡面极显著、沟道附近显著、沟道不显著的空间格局; 16年间生长季NDVI与气温无明显相关性,与降水的相关系数为-0.41～0.87,相比沟道附近植被而言,坡面上的植被更易受降水量影响;植被生长对降水的响应存在1年（P=0.036<0.05）和1个月（P=0.001<0.01）的滞后期,对气温存在2个月（P=0.002<0.01）的滞后期。【结论】时间上,皇甫川流域NDVI在不断波动中呈显著上升趋势,生长季与非生长季均值变化表现出明显不同。空间上,皇甫川流域NDVI在沟道均值高,但增长率低,甚至出现退化现象,在坡面均值低,但呈极显著增长。林地和草地增加最多,说明近年来退耕还林工程效果显著。NDVI与降水相关性较高并与气温和降水都存在一定滞后现象。更多还原

【Abstract】 【Objective】The purpose of this article is to explore the characteristics of temporal and spatial dynamic changes of vegetation coverage within Pisha sandstone area in Loess Plateau, to analyze the impact of the normalized difference vegetation index（NDVI） under different land use patterns,to discuss the spatial and time-delay relationship between vegetation coverage and hydrothermal factors. It provides ideas for the restoration and reconstruction of degraded vegetation within Pisha sandstone area in the Loess Plateau and the comprehensive management of the coarse sediment of the Yellow River. And it is beneficial to improving local living conditions and ecological environment in the Pisha sandstone area. 【Method】Huangfuchuan basin was chosen as the study area, and a total of 192 MODIS13Q1 products between 2000—2015 were used to obtain NDVI values based on ENVI technique. Characteristics of NDVI in temporal dynamics and spatial distribution were investigated with methods of univariate linear Regression（ULR） and Spearman correlation analysis. Spatiotemporal characteristics under different land use types, the resolution of which is 30 m, was statistically analyzed and the responses of vegetation coverage to changes of precipitation and temperature factors during growing season was further emphasized. 【Result】The average NDVI value of Huangfuchuan basin is ranged between 0.429 and 0.630, showing a linear increasing trend. The growth rate is 0.004 2·a^-1. Significant difference between the growing and non-growing seasons was detected, and the maximum value appeared in May. The temperature and precipitation also showed an increasing tendency with growth rates of 0.034 8 ℃·a^-1and 6.27 mm·a^-1, respectively. Spatially, the NDVI values range between 0.1-0.3 in subbasin of Nalin, and in the range of 0.25-0.4 within subbasin of Shilichangchuan. The vegetation shows a spatial pattern of "high in gully and low on slope" in two subbasins. The NDVI values of different land types were all between 0.2-0.25. The NDVI values in different land use types ranked as forest> cultivated land>grassland > unused land. The growth rate in past 16 years ranked as grassland > unused land> forest > cultivated land. For tributary of Nalin, NDVI near the gully decreased by-0.09-0, while NDVI on slopes far away from the gully increased by 0-0.12. For tributary of Shilichangchuan, NDVI near the gully increased by 0-0.4 while by 0.04-0.12 on slopes. Over the whole basin, variation tendency of vegetation cover shows a spatial increase pattern of "very significant on slope surface nearly significant in the vicinity of gully,non-significant in gully ". During the past 16 years, there was no significant correlation between NDVI and temperature in the growing season. The correlation coefficient between precipitation and NDVI was-0.41～0.87. Compared with the vegetation near the gully, vegetation on the slope was more susceptible to precipitation. Vegetation has 1-year（P=0.036< 0.05） and 1-month（P=0.001<0.01） lag time for precipitation, and 2-month（P=0.002<0.01） lag time for temperature. 【Conclusion】Temporally, NDVI in Huangfuchuan basin showed a significant decreasing trend of fluctuations, and obvious distinction was detected between the growing season and non-growing season. Spatially, in accordance with the gully-slope distribution, the gully showed high NDVI but low increasing rate and even appeared the phenomenon of degradation; meanwhile, the slopes showed low NDVI but high increasing rate. NDVI with land use types of forest and grassland increased the most, indicating the validity of the returning farmland to forest projects. The correlation between vegetation and precipitation is high, and there is a certain lag.更多还原