The annual frequency of ground surface freeze–thaw (AFGSFT) on the Qinghai-Xizang Plateau (QXP) is one of the most prominent features of the high plateau ground surface processes. Seasonal freezing and thawing of the ground surface led to changes, and sometimes anomalies, in the energy balance between the ground surface and the atmosphere, thereby impacting the ecological environment. However, the relationship between AFGSFT and normalized difference vegetation index (NDVI), as major influencing factors of near-ground surface hydrothermal processes, has not been well elucidated. Based on meteorological observation data from 1982 to 2020, National Oceanic and Atmospheric Administration Climate Data Record (NOAA CDR) NDVI data, and some auxiliary data, this study employs trend analysis, GeoDetector, and correlation analysis to explore the impact of NDVI on AFGSFT. The findings indicate that AFGSFT on the QXP has gradually decreased, while NDVI has generally shown an upward trend. NDVI exerts a strong controlling effect on AFGSFT changes. Specifically, as AFGSFT decreases, NDVI tends to increase, but the increasing NDVI gradually inhibits the downward trend of AFGSFT. Thus, the relationship between NDVI and AFGSFT trend is not merely one of amplification or inhibition but rather exhibits a more complex nonlinear relationship. Moreover, the changes in AFGSFT and NDVI in grassland areas are greater than those in other land cover types. This may suggest that grassland regions are experiencing a more rapid climate response and ground surface processes. These findings contribute to a better understanding of the ground surface characteristics of the high plateau and provide data support for formulating scientific ecological protection and climate adaptation strategies.

中文翻译：

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青藏高原地表冻融及其与植被覆盖的相互关系评价


青藏高原地表冻融 （AFGSFT） 的年频率 （QXP） 是高原地表过程最突出的特征之一。地表的季节性冻融导致地表与大气之间的能量平衡发生变化，有时甚至出现异常，从而影响生态环境。然而，AFGSFT 与归一化植被指数 （NDVI） 之间的关系作为近地表热液过程的主要影响因素，尚未得到很好的阐明。本文基于 1982 年至 2020 年的气象观测数据、美国国家海洋和大气管理局气候数据记录 （NOAA CDR） NDVI 数据以及一些辅助数据，采用趋势分析、GeoDetector 和相关性分析来探讨 NDVI 对 AFGSFT 的影响。研究结果表明，QXP 上的 AFGSFT 逐渐下降，而 NDVI 总体呈上升趋势。NDVI 对 AFGSFT 变化具有很强的控制作用。具体而言，随着 AFGSFT 的降低，NDVI 趋于增加，但 NDVI 的增加逐渐抑制了 AFGSFT 的下降趋势。因此，NDVI 和 AFGSFT 趋势之间的关系不仅仅是扩增或抑制的关系，而是表现出更复杂的非线性关系。此外，草地地区AFGSFT和NDVI的变化大于其他土地覆被类型。这可能表明草原地区正在经历更快速的气候响应和地表过程。这些发现有助于更好地了解高原地表特征，为制定科学的生态保护和气候适应策略提供数据支持。