Abstract
Abstract. Frozen ground covers a vast area of the Earth's surface and it has important ecohydrological implications for cold regions under changing climate. However, it is challenging to characterize the simultaneous transfer of mass and energy in frozen soils. Within the modeling framework of Simultaneous Transfer of Mass, Momentum, and Energy in Unsaturated Soil (STEMMUS), the complexity of the soil heat and mass transfer model varies from the basic coupled model (termed BCM) to the advanced coupled heat and mass transfer model (ACM), and, furthermore, to the explicit consideration of airflow (ACM–AIR). The impact of different model complexities on understanding the mass, momentum, and energy transfer in frozen soil was investigated. The model performance in simulating water and heat transfer and surface latent heat flux was evaluated over a typical Tibetan plateau meadow site. Results indicate that the ACM considerably improved the simulation of soil moisture, temperature, and latent heat flux. The analysis of the heat budget reveals that the improvement of soil temperature simulations by ACM is attributed to its physical consideration of vapor flow and the thermal effect on water flow, with the former mainly functioning above the evaporative front and the latter dominating below the evaporative front. The contribution of airflow-induced water and heat transport (driven by the air pressure gradient) to the total mass and energy fluxes is negligible. Nevertheless, given the explicit consideration of airflow, vapor flow and its effects on heat transfer were enhanced during the freezing–thawing transition period.
Highlights
Frozen soils have been reported to undergo significant changes under climate warming (Cheng and Wu, 2007; Hinzman et al, 2013; Biskaborn et al, 2019; Zhao et al, 2019)
On the basis of the STEMMUS modeling framework, with various representations of water and heat transfer physics (BCM, ACM, and ACM–AIR), the performance of each model in simulating water and heat transfer and surface evapotranspiration was evaluated over a typical Tibetan meadow ecosystem
The analysis of the heat budget components and latent heat flux density revealed that the improvement in soil temperature simulations by ACM is ascribed to its physical consideration of vapor flow and the thermal effect on water flow, with the former mainly functioning at regions above the evaporative front and the latter dominating below the evaporative front
Summary
Frozen soils have been reported to undergo significant changes under climate warming (Cheng and Wu, 2007; Hinzman et al, 2013; Biskaborn et al, 2019; Zhao et al, 2019). Changes in the freezing and thawing process can alter soil hydrothermal regimes and water flow pathways and, affect vegetation development (Walvoord and Kurylyk, 2016). Such changes will further considerably affect the spatial pattern, the seasonal to interannual variability, and long-term trends in land surface water, energy and carbon budgets, and the land surface–atmosphere interactions (Subin et al, 2013; Iijima et al, 2014; Schuur et al, 2015; Walvoord and Kurylyk, 2016).
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