Spatial and Temporal Changes of Vegetations and Its Topographic Effects on the Arid Valley Area of the Upper Reaches of Minjiang River from 2000 to 2020

doi:10.19657/j.geoscience.1000-8527.2024.034

Abstract

Abstract:

Considering the extremely fragile ecological characteristics in the arid valley area of Upper Reaches of Minjiang River (URMR), we inverted the Fractional Vegetation Cover (FVC) of the arid valley area of URMR from 2000 to 2020, using the NDVI data and the approach of image element dichotomy. We further qua.pngied the spatial and temporal variations of the FVC index using the linear analysis and F significance test. The relationship between FVC and altitude, slope, and aspect were analyzed in the arid valley area of URMR. The results showed that (1) the FVC index showed a fluctuating increasing trend from 2000 to 2020, and the annual average FVC increased from 0.62 in 2000 to 0.67 in 2020. (2) Spatially, FVC showed an increasing trend from the low altitude area to the high altitude one. FVC in the low and medium-low-grade was mainly distributed on the banks of the main stream and tributaries of the Minjiang River, while FVC in the medium and medium-high grade was distributed on both banks of Minjiang River, and FVC in the medium and medium-high grade was distributed in the URMR valley. FVC in the medium and high grade was distributed in the low and medium altitude mountains on both sides of the river valley, and FVC in the high grade was mainly distributed in the high and medium altitude mountains away from the river valley. (3) The area with a high vegetation coverage decreases and then increases with the increasing altitude, and the high vegetation coverage reaches to its peak in the altitude of 1,100-1,400 m and 3,200-3,500 m. The area with a high vegetation coverage increases with the slope, while the area with a high vegetation coverage shows an increasing and then decreasing trend with the increasing slope gradients. The areas with slopes of 10°-20° and 30°-40° were the peak of high and medium-high to high vegetation coverage. Overall, the vegetation coverage on the sunny slope was higher than that on shady side, and FVC index is greatly affected by the factors of altitude, slope, and aspect. Therefore, the effects of topography and local conditions should be considered in the ecological protection in the arid valley area of URMR.

Key words: vegetation coverage, spatial and temporal variability, topographic effect, Upper Minjiang River, arid river valley

CLC Number:

P931
Q948

ZHOU Xueni, XIAO Chengzhi, LIU Lei, JI Yang, CAO Yating, LI Xiaohong, BA Renji. Spatial and Temporal Changes of Vegetations and Its Topographic Effects on the Arid Valley Area of the Upper Reaches of Minjiang River from 2000 to 2020[J]. Geoscience, 2024, 38(03): 589-598.

Figures/Tables 8

Fig.1 Location of the study area and distribution of the water systems

Fig.2 Distribution of altitude, aspect, and slope in the arid valley area of URMR

Table 1 Data information and sources

数据	数据源	数据集
干旱河谷区范围	山地科学数据中心	西南地区干旱河谷区范围^[8]
NDVI	中国科学院地理科学与资源研究所土地利用与全球变化遥感团队	2000—2020年中国30 m年最大NDVI数据集^[9]
DEM	地理空间数据云(http://www.gscloud.cn/)	ASTER (30 m)
降雨数据	阿坝藏区羌族自治州公共气象服务中心	5个气象站点(黑水、理县、茂县、松潘、汶川)2000—2020年降雨数据

Fig.3 Spatial distribution of FVC (a), FVC interannual rates of change (b), and spatial distribution of average FVC trend (c) in the study area

Fig.4 Inter-annual variations of FVC in the arid valley area of URMR from 2000 to 2020

Fig.5 Changes in vegetation coverage at various levels of elevation (a), altitude differences in the change rates of FVC (b), and statistical map of vegetation coverage changes in different altitude (c) in the study area

Fig.6 Changes in vegetation coverage at various levels of aspect (a)(d), slope and aspect differences in FVC rates of change (b)(e), and statistical map of vegetation coverage changes in different slopes and aspect (c)(f)

Fig.7 Changes in the spatial distribution of various FVC grades in the study area

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