雅鲁藏布江流域不同海拔梯度下消落区植被NDVI的时空变化趋势及驱动因素

Temporal and spatial trends in NDVI of vegetation in water level fluctuation zone and drivers along an altitude gradient in the Yarlung Zangbo River Basin

消落区植被的生长变化一定程度上会影响水资源的可用性。雅鲁藏布江是中国、印度、孟加拉等国家的主要淡水水源地,流域内海拔落差大,气候的空间异质性较高。消落区在淡水生态系统保护中具有重要功能,但它易受到全球气候变化的影响,因此开展消落区植被对气候变化的响应研究对于保护雅鲁藏布江流域生物多样性和构建生态安全屏障具有重要意义。本研究选取雅鲁藏布江流域消落区植被作为研究对象,利用遥感技术,选取归一化植被指数(NDVI)进行了Theil-SenMedian趋势分析和Mann-Kendall检验,利用Hurst指数探究了长时间序列下消落区植被的时空变化趋势,并通过广义线性模型研究了消落区植被NDVI与气温、降水、雪水当量和水位波动频率等影响因素之间的相关性。结果表明,1990–2022年间,雅鲁藏布江流域消落区和1–5 km缓冲区的平均NDVI呈现西北低、东南高的变化趋势。时间尺度上,消落区植被NDVI总体呈波动上升趋势,其中最高值(0.16)和最低值(0.06)分别出现在2002年和2022年。年均NDVI的变化结果显示,中高海拔区域的NDVI持续增加,而中下游区域的NDVI变化不稳定。随着海拔升高,消落区和1–5 km缓冲区的NDVI持续减少和反持续减少的面积占比呈波动变化,海拔1,500–3,000 m地区受影响最为明显。水位波动频率是消落区NDVI的最佳解释变量之一,而温度则是缓冲区NDVI的主要影响因素。此外,随着海拔升高,雪水当量对NDVI的解释力逐渐增加。该研究对雅鲁藏布江流域的生物多样性保护和生态安全屏障的构建具有重要意义。

Aim:The important question of how riparian vegetation adapts to climatic and river hydrological changes is gaining global attention.Yet,the impact of snow and frequency of water level fluctuation on vegetation in the water level fluctuation zones remains underexplored.This study focuses on the response of the normalized difference vegetation index(NDVI)of riparian vegetation to climatic and hydrological changes in the basin of Yarlung Zangbo River,with an emphasis on understanding the impacts of snow and water level fluctuations in alpine fluctuation zones.Method:This study employed Theil-Sen Median trend analysis and Mann-Kendall test to evaluate spatiotemporal vegetation trends utilizing NDVI as a key indicator from 1990 to 2022 in the Yarlung Zangbo River Basin,focusing on both the water level fluctuation zone and the adjacent 1–5 km buffer zones.A generalized linear model was used to quantify influencing factors including temperature,precipitation,snow water equivalent,and frequency of water level fluctuation.Results:The spatial distribution of riparian vegetation’s NDVI demonstrated lower values in the northwest and higher in the southeast.Temporally,a notable fluctuating upward trend in NDVI was observed,reaching its peak in 2002(0.16)and its bottom in 2022(0.06).The annual NDVI progression revealed a consistent increase at mid-to-high altitudes,contrasting with the downstream areas’sustained and irregular declines.Altitudinal analysis indicated that the decrease in NDVI varied in both the water level fluctuation and buffer zones,but was especially prominent between 1,500–3,000 m.The frequency of water level fluctuations stood out as the primary determinant for riparian NDVI,while temperature predominantly influenced the buffer zone’s NDVI.Additionally,the role of snow water equivalent in explaining NDVI became increasingly significant with elevation.Conclusion:Vegetation in the water level fluctuation zone is influenced by various climatic and environmental factors,with water level fluctuations being pivotal.The importance of snow intensifies with increasing altitude,underscoring its significance in the spatial-temporal vegetation distribution.