Multiple time scale characteristics of permafrost temperature variations along the Qinghai–Xizang Highway

Temperature is an important dynamic attribute of permafrost, but analysis only in the time domain ignores important information in the frequency domain. A combined time–frequency analysis provides a deeper understanding of temperature variations, revealing the response of warm and cold permafrost to climate change under both embankments and natural ground surfaces. Using 17 years of semimonthly permafrost temperature data from boreholes below natural ground surfaces and embankments in warm and cold permafrost, multiple time scale characteristics of permafrost temperature were analyzed via wavelet transformation. The results show that permafrost temperatures have multiple time scale characteristics. Significant changes to all the main periods were observed near the permafrost table. The response of permafrost to climate change under embankments varied significantly for warm and cold permafrost. Trends for permafrost temperature were forecast using large-scale periods of variation in permafrost temperature. Such forecasts have direct significance for analysis of engineering stability and treatment of roadbed damage in cold regions.