Variations and driving factors of annual frequency of near-surface freeze‒thaw cycles in China‒Mongolia‒Russia from 1975‒2024

Annual near-surface freeze–thaw cycles (NSAFTCs) provide a direct measure of the number of times the ground surface freezes and thaws in a year. NSAFTCs are key indicators of climate–land interactions and environmental change and are essential for preventing freeze–thaw damage in cold regions and promoting sustainable ecological development. However, the temporal evolution of NSAFTCs across the China‒Mongolia‒Russia region and their driving factors remain relatively understudied. NSAFTCs exhibit pronounced latitudinal differentiation and strong topographic influences and can be classified into low-frequency (<73 times per year), medium-frequency (73–147 times per year) and high-frequency (>147 times per year). Based on daily temperature data from 2112 meteorological stations, NSAFTCs exhibited a significant upward trend from 1975 to 2024 (4.04 times per decade, p < 0.01). The increase was greatest (35–41 times per decade) in the Qinghai‒Tibet Plateau ( p < 0.05). Temperature ( q = 0.4328), latitude ( q = 0.3844) and elevation ( q = 0.3322) are the primary controlling factors. Under controlled temperature conditions, elevation remains a stable and independent key factor. Further analysis reveals a significant positive correlation between NSAFTCs and the annual mean temperature range ( AMTR ) ( p < 0.01), with an optimal temperature variation range of 12–16°C. High-elevation regions form a temperature gradient‒freeze‒thaw coupling zone within this range, which amplifies the freeze‒thaw activity. These findings enable a deeper understanding of near-surface freeze–thaw processes over large regions and provide supporting data for advancing science-based ecological protection and engineering construction strategies.