College of Water Sciences, Beijing Normal University, Beijing, 100875, China.
Department of Geography and Planning, University of Saskatchewan, Saskatoon, SK, S7N 5C8, Canada.
Environ Monit Assess. 2021 Jun 10;193(7):406. doi: 10.1007/s10661-021-09187-8.
Riparian vegetation cover is significantly affected by a river's hydrological conditions. Especially in arid and semiarid areas, low flow will degrade riparian vegetation, and recent, intensive human activities in the Yongding River Basin have caused a sharp decrease in river flow. We analyzed interannual change in riparian vegetation, river flow effects, and land use on vegetation coverage using the 40 years (1977-2016) of remote sensing images and river flow, combined with 38 years (1980-2018) of land use data. The normalized difference vegetation index (NDVI) was used to determine vegetation cover in five different categories: extremely low, low, medium, high, and extremely high based on the pixel dichotomy model. The weighted average was calculated to obtain vegetation cover trends. We show that riparian vegetation cover from four rivers increased. Compared with 1977, in 2016, combined high and extremely high vegetation covers at the Dongyang, Yang, Sanggan, and Yongding Rivers increased by 20.3%, 26.7%, 50.0%, and 39.2%, respectively. High (R = -0.976, P < 0.01) and extremely high (R = -0.762, P < 0.05) vegetation covers are negatively correlated with flow in the Yongding River. The high vegetation cover of the Sanggan River riparian zone is negatively correlated with river flow (R = -0.683, P < 0.05). In the Dongyang and Sanggan Rivers, land use analysis in the riparian zone showed that change in cultivated land, grassland, and forest were significantly correlated with high and extremely high vegetation cover. The abundant cultivated land and restoration activities are likely responsible for the increase of riparian vegetation cover as river flows decline.
河岸植被覆盖受河流水文条件的显著影响。特别是在干旱和半干旱地区，低流量会导致河岸植被退化，而永定河流域最近的人类活动强度加大，导致河流流量急剧减少。我们利用 40 年（1977-2016 年）的遥感图像和河流流量，结合 38 年（1980-2018 年）的土地利用数据，分析了河岸植被、河流流量变化以及土地利用对植被覆盖的年际变化。利用归一化植被指数（NDVI），根据像素二分模型将植被覆盖分为极低、低、中、高和极高五个不同类别，并计算加权平均值以获得植被覆盖趋势。结果表明，四条河流的河岸植被覆盖面积增加。与 1977 年相比，2016 年东洋河、洋河、桑干河和永定河的高植被和极高植被覆盖率分别增加了 20.3%、26.7%、50.0%和 39.2%。高植被覆盖区（R=−0.976，P<0.01）和极高植被覆盖区（R=−0.762，P<0.05）与永定河流量呈负相关。桑干河河岸带高植被覆盖区与河流流量呈负相关（R=−0.683，P<0.05）。在东洋河和桑干河，河岸带土地利用分析表明，耕地、草地和林地的变化与高植被覆盖和极高植被覆盖显著相关。丰富的耕地和恢复活动可能是导致河流流量减少时河岸植被覆盖增加的原因。
