Abstract:

At present, there are few studies using NDVI data to evaluate the vegetation change trend of the Fenhe River Basin by considering the absolute area difference of different terrains over long time spans, so as to scientifically understand the vegetation change and topographic effect of the Fenhe River Basin. Based on MODIS NDVI data from 2000 to 2021, coupled with topographic data, this paper analyzes the spatial and temporal distribution and evolution characteristics of vegetation in the Fenhe River Basin by linear trend analysis and topographic difference correction, and discusses the differences in growth changes in elevation, aspect and slope. The results showed that (1) in the past 22 years, the NDVI of vegetation in the Fenhe River basin had a distribution pattern of low in the middle of the basin, high in the periphery, low in the basin, and lower in the plateau area than in the high in the mountain area, with significant changes as the terrain and land cover type varoed. From 2000 to 2021, the vegetation in the Fenhe River basin showed an overall trend of improvement, with an annual change rate of 0.07/(10 a). Among them, 63.24% of the regional vegetation NDVI increased significantly, and 33.78% of the regional vegetation basically remained unchanged. (2) The distribution and change of vegetation NDVI in the Fenhe River Basin had obvious topographic effects. With the increase of altitude, the NDVI of vegetation first decreased, then increased and finally decreases, and the NDVI was the largest in the range of 2200-2400 m altitude; the NDVI difference of vegetation in different slope directions was small, but the north slope was larger than the south slope, the east slope was larger than the west slope, and the northeast slope was the largest; as the slope increased, the NDVI of vegetation increased stepwise, and the NDVI was the largest in the 20°-35° slope. (3) From 2000 to 2021, the annual change of NDVI of vegetation in different landforms in the Fenhe River basin showed an improvement trend, but the NDVI of vegetation with an elevation of 800-1400 m and a slope of 3°-8° increased significantly; in the flat area with an altitude of 600-800 m and a slope of less than 1°, the annual increase rate of NDVI of vegetation was small, and the significant degradation distribution was obvious; the NDVI of vegetation in the transition area with an altitude of 600-1000 m, 1200-1400 m, and a slope of 1°-3° and 8°-9°, from flat land to different slope directions, was prone to fluctuate, and is the focus of ecological governance and an area to be strengthened. Therefore, the topographic effect of vegetation change should be paid attention to in the vegetation protection and regional ecological management of the Fenhe River basin.

Key words: Fenhe River Basin, Vegetation, NDVI, climate change, terrain effect, spatiotemporal evolution

摘要：

运用NDVI数据在长时序上考虑不同地形绝对面积差异来评价汾河流域植被变化趋势的研究目前比较匮乏。为科学认识汾河流域植被变化及其地形效应，基于2000-2021年的MODIS NDVI数据并结合地形数据，采用线性趋势分析与地形差异修正的方法，分析了汾河流域植被的时空分布及演变特征，并探讨了其在海拔、坡向和坡度上的生长变化差异。结果表明，（1）近22年汾河流域植被NDVI呈流域中部低、外围高、低海拔盆地平川区小于高海拔山脉区的分布格局，随地形和土地覆盖类型变化规律性显著。2000-2021年汾河流域植被总体呈改善趋势，年际变化速率为0.07/(10 a)，其中，63.24%的区域植被NDVI显著增加，33.78%的区域植被基本不变。（2）汾河流域植被NDVI分布和变化存在明显的地形效应，随着海拔递增，植被NDVI先减小后增大再减小，2200-2400 m海拔范围内NDVI最大；不同坡向的植被NDVI差异较小，但总体北坡大于南坡、东坡大于西坡，东北坡最大；随着坡度增加，植被NDVI阶梯式增大，20°-35°坡度范围内NDVI最大。（3）2000-2021年汾河流域不同地形的植被NDVI年际变化均呈改善趋势，但在海拔为800-1400 m、坡度为3°-8°的区域植被NDVI以显著增加为主；在海拔为600-800 m、坡度小于1°的平地区域植被NDVI年际增加速率较小，显著退化分布明显；在海拔为600-1000、1200-1400 m、坡度为1°-3°和8°-9°，由平地转为不同坡向的过渡区植被NDVI易出现波动，是生态治理注重和加强区。因此，在汾河流域植被保护及区域生态管理中应关注植被变化的地形效应。

关键词: 汾河流域, 植被, NDVI, 气候变化, 地形效应, 时空演变