基于机器学习的黄河源区高寒灌丛覆盖度反演及时空演变分析
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1.兰州理工大学;2.中国科学院西北生态环境资源研究院

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国家重点研发计划项目(2023YFC3206300),甘肃省自然科学基金(24JRRA176),甘肃省科技专员专项(24CXGA063)


Analysis of the temporal and spatial evolution of the coverage of alpine shrubland in the Yellow River source area based on machine learning
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Lanzhou University of Technology

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    摘要:

    黄河源区(以下简称为源区)位于青藏高原多年冻土区和季节冻土区的过渡区,境内广泛分布被称为气候变化指示器的高寒灌丛。在气候变化及冻土退化的背景下,灌丛扩张现象已引起广泛关注,目前的研究多局限于小尺度,难以了解全域灌丛的时序覆被状况。基于此,本文以源区高寒灌丛为研究对象,以Landsat 8遥感影像和无人机航拍数据为基础数据源,运用随机森林、支持向量机和人工神经网络等机器学习方法对源区2014-2024年高寒灌丛覆盖度进行逐年反演;结合地形、气象等数据,通过数理统计等方法对源区多年灌丛的空间分布格局进行分析;利用变异系数(CV)、Sen+Mann-Kendall趋势分析和Hurst指数等方法进行源区灌丛时空演变分析。结果表明:(1)三种反演模型中,随机森林表现最优,其训练集、测试集的R2分别为0.91、0.85,RMSE分别为0.05、0.07,一致性指数d均达到0.95以上,表明该模型更适合进行源区高寒灌丛覆盖度的反演。(2)随机森林模型的反演结果显示:源区高寒灌丛面积约占源区总面积的10.2%,主要分布在源区季节性冻土区的黄河干流及支流沿线沟谷中,且灌丛覆盖度相对较高,而在源区多年冻土区,灌丛分布较少。(3)时空演变分析结果显示:在空间分布上,源区77.93%的灌丛处于稳定区;趋势分析表明:2014-2024年源区灌丛显著上升区域占72.21%,不显著上升区域占11.36%;Hurst指数结合Sen斜率结果表明在源区85.99%的区域未来呈现趋势持续特征。研究结果可为高寒灌丛空间变化监测及灌丛对气候变暖和冻土退化的响应机制提供精细数据。

    Abstract:

    The Source region of Yellow River (hereafter referred to as the source region) is located in the transition zone between the permafrost and seasonal permafrost zones on the Qinghai-Tibet Plateau, and alpine shrubs, recognized as indicators of climate change, are widely distributed in the Source Region. Against the backdrop of climate change and permafrost degradation, the phenomenon of shrub expansion has attracted widespread attention. However, current studies are mostly confined to small scales, making it difficult to understand the temporal coverage status of shrubs across the entire region. This paper focuses on the cold alpine shrubs in the source region, using Landsat 8 remote sensing images and drone aerial photography data as the primary data sources.,and applying machine learning methods such as random forests, support vector machines, and artificial neural networks to retrieve the alpine shrub coverage in the source region from 2014 to 2024., mathematical statistics methods are used to analyze the spatial distribution patterns of shrubs combined with data of topography, meteorology, and other factors over the years in the source area. Methods such as the coefficient of variation (CV), Sen Mann-Kendall trend analysis, and Hurst index are utilized for analyzing the spatiotemporal evolution of shrubs in the source area. The results show that: (1) Among the three inversion models, the random forest performs the best, with R2 values of 0.91 and 0.85 for the training and testing sets respectively, RMSE values of 0.05 and 0.07, and consistency indices (d) exceeding 0.95, indicating that this model is more suitable for inverting the cold alpine shrubs in the source area. (2) The inversion results from the random forest model indicate that the area of cold alpine shrubs in the source area accounts for approximately 10.2% of the total area, mainly distributed along the valleys of the main stream and tributaries of the Yellow River within the seasonal frost zone of the source area, with a relatively high shrub coverage, while shrub distribution is sparse in the permafrost regions of the source area. (3) The results of the spatiotemporal evolution analysis show that in terms of spatial distribution, 77.93% of the shrubs in the source area are in stable zones; trend analysis indicates that from 2014 to 2024, the significantly increasing areas of shrubs in the source area account for 72.21%, while the non-significantly increasing areas account for 11.36%; results from the Hurst index combined with Sen slope analysis indicate that 85.99% of the source area is showing characteristics of sustained trends in the future. The research results can provide detailed data for monitoring spatial changes in cold alpine shrubs and understanding the response mechanisms of shrubs to climate warming and permafrost degradation.

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周兆叶,边雁君,王雪平,吴晓东,李旺平,王牛,王聪,尹宽勃,邹德富.基于机器学习的黄河源区高寒灌丛覆盖度反演及时空演变分析.生态学报,,(). http://dx. doi. org/[doi]

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