基于地形位置指数的赤水河流域植被时空变化研究

地形因子和植被覆盖是区域灾害评价的关键指标，也是山区型村镇建设生态安全评估的重要内容.为探析山区型村镇建设的生态约束条件，以赤水河流域为研究对象，基于1998—2018年SPOT_VGT NDVI数据，利用地形位置指数（Topographic Position Index，TPI）和坡度位置指数方法，研究了赤水河流域植被生长季NDVI时空变化及地形分异特征.结果表明:①赤水河流域内，1998—2018年植被生长季平均NDVI呈缓慢上升趋势，斜率为0.004 7；NDVI>0.60的集中连片区域主要分布在古蔺县北部、赤水市大部和习水县西北部，占赤水河流域总面积的8.42%；Sen's slope在0.009~0.015区间时，赤水河流域植被生长增强趋势最明显，主要集中分布在赤水河中上游、二道河以及下游的大同河干流地区.②TPI在-39.4~34.3区间的面积最多，为6 221.63 km2，占赤水河流域总面积的34.05%；将赤水河流域坡度类型划分为山脊、上坡、中坡、平坡、下坡、山谷6个坡度位置类型，其中，中坡面积（7 792.02 km2）最大，占流域总面积的42.64%，表明TPI数值较小且坡度大于5°的区域是赤水河流域地形主体.③赤水河流域植被在山脊的平均NDVI最高，为0.747，且山脊平均Sen's slope最高，为0.007 2；山谷平均NDVI最低，为0.709.研究显示，赤水河流域植被分布在118.5~486.9的TPI区间或分布在山脊处时整体生长较好，且生长增强趋势最明显. 

Spatiotemporal Changes of Vegetation in Chishui River Basin Based on Topographic Position Index

Terrain factors and vegetation coverage are the key indicators for regional disaster assessment, and are important factors for ecological security assessment of mountainous villages and towns. In order to analyze the ecological constraints of the construction of mountainous villages and towns, in this study, the Chishui River Basin was used as an example to analyze the ecological constraints for the construction of mountainous villages and villages, and the topographical variation characteristics of the vegetation was investigated using the 1998-2018 SPOT_VGT NDVI product data, the Topographic Position Index (TPI), and slope position method. The results show that: (1) From 1998 to 2018, the average NDVI value of vegetation growth season showed a slow upward trend with a slope of 0.0047; while the concentrated contiguous areas with NDVI greater than 0.60 were mainly distributed in the northern part of Gulin County, most of Chishui City and northwestern part of Xishui County, accounting for 8.42% of the total area of the Chishui River Basin. When the Sen''s slope value was in the range of 0.009 to 0.015, the vegetation in Chishui River Basin had the highest growth trend; these areas were mainly located in the middle and upper reaches of the Chishui River, the mainstream of the Erdao River, and the mainstream of the downstream Datong River. (2) TPI had the largest area in the range of -39.4 to 34.3, which was 6221.63 km², accounting for 34.05% of the total basin area. The slope types of the Chishui River Basin were divided into six slope position types: ridge, upslope, mid-slope, flat slope, downslope, and valley. Among them, the area of middle slope (7792.02 km²) was the largest, accounting for 42.64% of the total area of the basin, indicating that the slope position area with a smaller TPI value and a slope greater than 5° was the main terrain of the Chishui River Basin. (3) In the Chishui River Basin, the highest average NDVI value of the ridge was 0.747 with the highest average Sen''s slope value, up to 0.0072; the average NDVI value of the valley slope position is the lowest, 0.709. Studies show that the vegetation in the Chishui River Basin grows better when distributed in the TPI range of 118.5-486.9 or at the position of the ridge slope, and the growth trend is the strongest.