基于地形梯度的汾河流域土地利用时空变化分析

地形在一定程度上影响着土地利用变化,对土地利用空间格局的形成具有重要作用,因此,分析土地利用类型与地形因子的动态关系可以反映土地利用变化的合理性,对后续的土地利用管理和水土保持有重要的意义。基于汾河流域1986年、1995年、2005年和2010年土地利用矢量图,构建土地利用变化图谱和地形位指数,系统分析了土地利用在地形梯度上的分布特征和变化历程。结果表明:1986-2010年,土地利用类型以耕地、林地和草地为主,其中耕地减少和建设用地增加是主要变化类型。各地类在地形梯度上呈明显的层级分布,耕地、建设用地和水域主要分布在低地形梯度,草地分布在中区段,而林地集中分布在中高区段。土地利用变化以稳定型和反复变化型为主,两者占研究区总面积的98.4%,其中,稳定型以低地形梯度的耕地和中高地形梯度的林地为主,反复变化型以低中地形梯度的草地与耕地间的反复转化为主;其余图谱类型的比例均在1%以下,主要变化类型均为中低地形梯度下耕地向建设用地的转化。在自然因素、人类活动和政策的共同作用下,汾河流域的土地利用结构和空间格局发生了改变,整体趋于合理,但仍存在部分不合理利用现象,需要加强规划管理。

Spatiotemporal variations analysis for land use in Fen River Basin based on terrain gradient

Abstract: Land use/cover change (LUCC) is a key component of global climate change, and it has great impacts on climate, hydrological processes, biodiversity and ecological processes. Therefore, more attentions have been paid to LUCC. As land use pattern is significantly influenced by topographical factors that indirectly has impacts on water and surface energy balance, analysis of land use pattern is thus a useful method to assess the rationality of LUCC according to the variations in their topographic factors, which will further provide important information for land use management and soil conservation. Fen River Basin is one of the regions with most severe soil loss on the Loess Plateau, and it has been experiencing great changes in land use pattern due to the implementation of soil conservation measures. After using land use data of 1986, 1995, 2005 and 2010 to analyze the temporal and spatial variation in land use from 1986-2010, and using terrain niche index derived from DEM (digital elevation model) to represent the topographical factors of different land use patch, the relationship between terrain and land use change was systematically analyzed. Results showed that from 1986 to 2010, the main land use types of the study region were farmland, forest and grassland, which account for 94% of the whole catchment, and the main land use change types were the decrease of farmland and the increase of urban and residential land. The rate of land use change for the period of 1986-1995, 1995-2005 and 2005-2010 were 13.2%, 25.8% and 36.4%, respectively, indicating a speed-up land use changes. But for the whole study period, the land use change rate was 1.3%, which implied that the land use pattern was recovering the original status with less human disturbance. Our results also showed that the spatial distribution of land use types had close relationships with terrain gradient. The farmland, urban/residential land and water sources were mainly located in the areas with low terrain gradient, while grassland in the areas with middle terrain gradient and forest in the areas with mid-high terrain gradient. According to the land use change TUPU, we found that the primary land use change types were stable type and repeated change type, which accounted for 98.4% of the whole catchment. The stable land use change type was mainly composed of forest with large terrain gradient and farmland with small low terrain gradient, while the repeated change type mainly from the mutual conversion between grassland and farmland at areas with mid-low terrain gradients. In addition, the results indicated that LUCC in the Fen River Basin was the combined effect of natural processes, human activities and government policies. The natural processes played a key role in the impacts of terrain gradient effect on land use change, while human activities and policies were very important drivers that can make land use change rapidly in a short time period. Overall, the land use pattern in the Fen River Basin has been becoming rational. However, some improper land use change types were also detected. Based on analyzing the rationality of land use change by topographical factors, this study was meaningful to the sustainable development of land resources, and it can provide important information for land use management in the Fen River Basin.