Changes in the hydrological and thermal regime of permafrost bogs in the past 50 years: synthesis of observational data and modelling.

Two types of frozen bogs, palsa mires and polygonal marshes, occupy up to 30 % of the permafrost terrain in West Siberia. Palsa mires span the territory from the Arctic Circle down to approximately 62° N in continuous, discontinuous and sporadic permafrost zones; polygonal marshes are located northward from the Arctic Circle. The hydro-thermal regime of permafrost bogs is characterized by three key parameters, namely, soil temperature, active-layer thickness (ALT), and soil water table depth. We used the CryoGrid community model with daily ERA-5 reanalysis meteorological data to study changes in these parameters in the period 1971–2024. The model was calibrated using an extensive historical data set of the State Hydrological Institute for 10 permafrost bog plots, which was built up in the course of the field expeditions in West Siberia in the 1971–1992 period. The calibrated CryoGrid model demonstrated reasonably good performance in reproducing observed parameters of the hydro-thermal regime of permafrost bogs in a variety of climatic, bio-physiographic and permafrost conditions. The mean square errors of the calculated parameters for polygonal marshes/palsa mires were the following: ALT error (3.8 ÷ 5.6 cm)/(5.2 ÷ 5.9 cm); soil temperature error (1.2 ÷ 1.5 °C)/(0.8 ÷ 1.3 °C) and soil water level error (6.8 ÷ 10.5 cm)/(7.9 ÷ 9.7 cm). The modelling results suggest that changes in the hydro-thermal regime of permafrost bogs have increased in the past 25 years. Calculated over the 2000–2024 period trends, averaged over the areas occupied by polygonal marshes and palsas, were, correspondingly, as follows: 1.35 and 1.10 °С/10y for soil temperature at 20 cm depth; 9.6 and 5.2 cm/10y for ALT; –1,1 and –2,9 cm/10y for soil water levels.