Thickened active layer contribute less to vegetation growth over the Tibetan Plateau

• The mean active layer thickness on the Tibetan Plateau ranged from 1.03 to 3.73 m. • Permafrost vulnerability on the TP is indeed influenced by global climate extremes. • 52% of the meltwater on the Tibetan Plateau may accumulate in the permafrost layer. • The mean contribution rate of permafrost meltwater to vegetation is under 2.29%. Considering that active layer (AL) thickening is a phenomenon of permafrost degradation, early observations primarily focused on frozen ground types (i.e., permafrost and seasonally frozen ground) or the Active Layer Thickness (ALT). However, existing studies have paid little attention to the correlation between lateral degradation of permafrost and vertical thickening of the AL, as well as the contribution of meltwater during the thickening of the AL to vegetation greening on a large scale. Using 1,053 records of AL observation data from 2000 to 2020, five causal relationship models, and three data-driven methods, this study estimates the relationship between the vertical evolution trend of ALT and the lateral degradation of permafrost, while also exploring the contribution of meltwater from permafrost to vegetation growth. The results indicate that the average ALT on the Tibetan Plateau (TP) ranged from 1.03 to 3.73 m during 2002–2020. Furthermore, the TP is delineated by the Yarlung Zangbo, Nujiang, Lancang, Yangtze, and Yellow River basins. Permafrost degradation in the northwest region accelerates the thickening of AL in permafrost areas at a rate of 0.006 m/a. In contrast, in the southeast, it accelerates the thickening of AL in degraded permafrost areas at a rate of 0.004 m/a. Meanwhile, frozen ground degradation is more susceptible to extreme values of temperature, Land surface temperature, precipitation, and wind speed. During the thawing process, soil moisture may accumulate in deeper layers, resulting in an average contribution rate of the altered hydrological environment caused by degraded permafrost to vegetation growth of less than 2.29 %. This research provides a deeper understanding of the interactions among frozen ground, soil, and vegetation at a large scale. The interannual variations in ALT will further reduce the uncertainty about the thermal state of permafrost and its future response.