Soil infiltration processes were evaluated under field conditions by double-ring infiltrometers with different underlying surfaces in permafrost regions of the Tibetan Plateau. The results show that initial infiltration rates, stable soil infiltration rates and cumulative soil infiltration are strongly dependent on the underlying surface types, with the highest initial and stable soil infiltration rates in the alpine desert steppe, and the lowest in alpine meadow. The effects of soil moisture and texture on infiltration processes were also assessed. Within the same underlying surfaces, the values of infiltration parameters increased with the amount of vegetation cover, while soil moisture and soil infiltration rates displayed opposing trends, with fitting slopes of -0.03 and -0.01 for the initial and stable soil infiltration rates, respectively. The accuracies of the five models in simulating soil infiltration rates and seven models in predicting cumulative infiltration rates were evaluated against data generated from field experiments at four sites. Based on a comparative analysis, the Horton model provided the most complete understanding of the underlying surface effects on soil infiltration processes. Altogether, these findings show that different underlying surfaces can alter soil infiltration processes. This study provides a useful reference for understanding the parameterization of land surface processes for simulating changes in hydrological processes under global warming conditions in the permafrost region on the Tibetan Plateau.

Changes in the hydrological processes in alpine soil constitute one of the several key problems encountered with studying watershed hydrology and ecosystem stability against the background of global warming. A typically developing thermokarst lake was chosen as a subject for a study using model simulation based on observations of soil physical properties, infiltration processes, and soil moisture. The results showed that the selected thermokarst lake imposed certain changes on the soil infiltration processes and, with the degree of impact intensifying, the initial infiltration rate decreased. The greatest reduction was achieved in the area of moderate impact. However, the stable infiltration rate and cumulative infiltration gradually increased in the surface layer at a depth of 10 and 20 cm, both decreasing initially and then increasing, which is correlated significantly with soil textures. Moreover, the cumulative infiltration changed in line with steady infiltration rate. Based on a comparative analysis, the Horton model helps better understand the effect on the soil infiltration processes of the cold alpine meadow close to the chosen thermokarst lake. In conclusion, the formation of the thermokarst lake reduced the water holding capacity of the alpine meadow soil and caused the hydraulic conductivity to increase, resulting in the reduction of runoff capacity in the area of the thermokarst lake.