Effect of increasing rainfall on the thermal—moisture dynamics of permafrost active layer in the central Qinghai—Tibet Plateau

Abstract

In the past several decades, the trend of rainfall have been significantly increasing in the Qinghai-Tibet Plateau, which inevitably leads to a change in the surface energy balance processes and thermal-moisture status of the permafrost active layers. However, the influence of mechanisms and associated effects of increasing rainfall on active layers are still poorly understood. Therefore, in this study, a validated coupled numerical water-vaporheat model was applied for simulating the surface energy components, liquid and vapor water migration, and energy transfer within the permafrost active layer under the action of increasing rainfall in the case of an especially wet year. The obtained results demonstrate that the surface heat flux decreases with the increase in rainfall, and the dominant form of energy exchange between the ground and atmosphere becomes the latent heat flux, which is beneficial for the preservation of permafrost. The increasing rainfall will also cause the migration of liquid and vapor water, and the migration of liquid will be more significant. The liquid and vapor water migration caused by the increasing rainfall is also accompanied by energy transfer. With the increase in rainfall, the decrease in total soil heat flux directly leads to a cooling effect on the soil, and then the upper limit of the frozen soil rises, which alleviates the degradation of permafrost. These results provide further insights into engineering structures, regional ecological climate change, hydrology, and environmental issues in permafrost regions.

Convective heat transfer of spring meltwater accelerates active layer phase change in Tibet permafrost areas

“…Those findings are not in conflict. Summer precipitation has multifaceted non-conductive effects, including cooling the topsoil through enhanced evapotranspiration from the ground surface, modifying soil properties such as heat capacity and conductivity by adding more liquid water to the soil (Zhou et al, 2021), rapidly transporting external heat to the soil through percolation, and pro-viding heat for the melting process occurring at the freezethaw front as a heat source when additional liquid water accumulates above the front (G. . In this study, hydraulic and hydrological functions of precipitation are the same in the scenarios; therefore, only the effect of rapid transportation of external heat into the soils is associated with the CHT process under investigation, which was found to be of less importance among the diverse effects of summer precipitation.…”

Thermal-Moisture Dynamics at Different Underlying Surfaces in Permafrost Regions of the Central Tibetan Plateau by considering the Effect of Rainfall

“…As shown in Table 2, the processed statistics indicate that the verification results of the temperature at 5, 15,25,35,75,150,160,170,200, and 220 cm depths are d > 0:802 and jMBEj < 1:204 °C. Meanwhile, the result is d > 0:853 and MBE < 1:353% for the water content [4,28]. A deviation of 2~3 °C from the measured soil temperature is regarded as acceptable [35].…”

“…θ l and θ i are the volume contents of liquid and vaporous phases of water (m 3 /m 3 ). The detailed hydraulic properties can be referred to in the research by Zhang et al [27,28].…”

“…The model has been used in different application scenarios and engineering environments. The reliability is high [27,28]. The NG, AP, and GP are some of the typical underlying surfaces in the central QTP.…”

“…The role of rainfall and evaporation was considered in the moisture boundary theory. A numerical model established by our team that has been well validated and applied was used in the study [4,27,28]. The typical underlying surfaces, such as asphalt pavement (AP), gravel pavement (GP), and natural ground (NG) of an alpine meadow in the central QTP, were taken as research objects.…”