Spatio-temporal changes in the annual frequency of freeze-thaw cycles in Russia

The annual frequency of freeze-thaw cycles (AFFTC) on the Earth's surface affects many natural components: landscape, ecosystems, engineering infrastructure, etc. However, the nature of changes over time and the driving forces of the AFFTC for the territory of Russia today remains largely undocumented. Based on an analysis of archival meteorological materials from more than 500 meteorological stations and posts, including those dating back to the last century, the article proposes zoning schemes for individual regions of Russia according to AFFTC data. Using a statistical tool based on the phenomenon of spatially stratified heterogeneity (SSH), the influence of various factors (air temperature, precipitation, etc.) on AFFTC was assessed. In the study area from 2005 to 2023, in comparison with 1980, areas with a higher value of AFFTC are shown to have increased. It is also confirmed that latitude and altitude are the variables with the greatest explanatory power, i.e., having the greatest influence on the AFFTC. Altitude above sea level has a particularly significant impact on the AFFTC in the range of 541–1850 m when the average annual air temperature is in the range of −3.9 … −0.8 °C. The observed formation of AFFTC features at the regional level appears to have a universal character and can thus be applied to solve a wide range of problems in assessing and forecasting climatic conditions, explain engineering-geological properties and predicting the degree of cryogenic transformation of soils with various structural connections, as well as forming a basis for recommending measures for environmental management and developing corresponding engineering construction standards.