Frozen ground degradation under a warming climate profoundly influences the growth of alpine vegetation in the source region of the Qinghai-Tibet Plateau. This study investigated spatiotemporal variations in the frozen ground distribution, the active layer thickness (ALT) of permafrost (PF) soil and the soil freeze depth (SFD) in seasonally frozen soil from 1980 to 2018 using the temperature at the top of permafrost (TTOP) model and Stefan equation. We compared the effects of these variations on vegetation growth among different frozen ground types and vegetation types in the source region of the Yellow River (SRYR). The results showed that approximately half of the PF area (20.37% of the SRYR) was projected to degrade into seasonally frozen ground (SFG) during the past four decades; furthermore, the areal average ALT increased by 3.47 cm/yr, and the areal average SFD decreased by 0.93 cm/yr from 1980 to 2018. Accordingly, the growing season Normalized Difference Vegetation Index (NDVI) presented an increasing trend of 0.002/10yr, and the increase rate and proportion of areas with NDVI increase were largest in the transition zone where PF degraded to SFG (the PF to SFG zone). A correlation analysis indicated that variations in ALT and SFD in the SRYR were significantly correlated with increases of NDVI in the growing season. However, a rapid decrease in SFD (< −1.4 cm/10yr) could have reduced the soil moisture and, thus, decreased the NDVI. The NDVI for most vegetation types exhibited a significant positive correlation with ALT and a negative correlation with SFD. However, the steppe NDVI exhibited a significant negative correlation with the SFD in the PF to SFG zone but a positive correlation in the SFG zone, which was mainly limited by water condition because of different change rates of the SFD.

中文翻译：

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1980—2018年黄河源区植被对冻地退化的不同响应

气候变暖下冻地退化深刻影响青藏高原源区高寒植被生长。本研究利用多年冻土顶部的温度 (TTOP) 调查了 1980 年至 2018 年季节性冻土中冻土分布、多年冻土 (PF) 活动层厚度 (ALT) 和土壤冻结深度 (SFD) 的时空变化。 ) 模型和 Stefan 方程。我们比较了这些变化对黄河源区（SRYR）不同冻土类型和植被类型之间植被生长的影响。结果表明，在过去的 40 年中，预计约有一半的 PF 区域（SRYR 的 20.37%）将退化为季节性冻土 (SFG)；此外，面积平均 ALT 增加了 3.47 厘米/年，1980-2018年区域平均SFD下降0.93 cm/yr。相应地，生长季归一化差异植被指数(NDVI)呈现0.002/10yr的上升趋势，其中NDVI上升的地区增加幅度和比例最大在 PF 退化为 SFG 的过渡区（PF 到 SFG 区）。相关性分析表明，SRYR中ALT和SFD的变化与生长季NDVI的增加显着相关。然而，SFD 的快速下降（< -1.4 cm/10yr）可能会降低土壤水分，从而降低 NDVI。大多数植被类型的 NDVI 与 ALT 呈显着正相关，与 SFD 呈负相关。然而，