Development of an enthalpy‐based frozen soil model and its validation in a cold region in China

Abstract

An enthalpy-based frozen soil model was developed for the simulation of water and energy transfer in cold regions. To simulate the soil freezing/thawing processes stably and efficiently, a three-step algorithm was applied to solve the nonlinear governing equations: (1) a thermal diffusion equation was implemented to simulate the heat conduction between soil layers; (2) a freezing/thawing scheme used a critical temperature criterion to judge the phase status and introduced enthalpy and total water mass into freezing depression equation to represent ice formation/melt and corresponding latent heat release/absorption; and (3) a water flow scheme was employed to describe the liquid movement within frozen soil. In addition, a parameterization set of hydraulic and thermal properties was updated by considering the frozen soil effect. The performance of the frozen soil model was validated at point scale in a typical mountainous permafrost basin of China. An ice profile initialization method is proposed for permafrost modeling. Results show that the model can achieve a convergent solution at a time step of hourly and a surface layer thickness of centimeters that are typically used in current land surface models. The simulated profiles of soil temperature, liquid water content, ice content and thawing front depth are in good agreement with the observations and the characteristics of permafrost. The model is capable of continuously reproducing the diurnal and seasonal freeze-thaw cycle and simulating frozen soil hydrological processes.Significant progress has been achieved over recent decades in modeling ground freezing and thawing and coupling these processes to hydrological and land surface models. A semiempirical permafrost model BAO ET AL.AN ENTHALPY-BASED FROZEN SOIL MODEL 5259

Evaluation of Noah Frozen Soil Parameterization for Application to a Tibetan Meadow Ecosystem

“…In other LSMs, there is an alternative numerical algorithm within which the I lat is ignored at first while solving the thermal diffusion equation, then the phase change is evaluated, and the soil temperature as well as the ratio of liquid water and ice contents is readjusted by energy conservation during the phase change. Such treatment of I lat is commonly employed in LSMs, such as Noah-MP (Niu et al 2011); Community Land Model (CLM; Oleson et al 2013); Interactions between Soil, Biosphere, and Atmosphere (ISBA) model (Decharme et al 2011;Masson et al 2013); and a modified Simple Biosphere Model (Bao et al 2016) because of its numerical efficiency. For instance, the treatment of I lat in Noah-MP (Niu et al 2011) is as follows: …”

“…The k h parameterization currently adopted by the Noah LSM (see section 2a) has recently been modified to represent the Tibetan frozen soil conditions by Bao et al (2016): Tables 1 and 2 as well. Notably, the overestimation of nighttime surface temperature is resolved with the implementation of new k h parameterization (Fig. 5c) that reduces the heat conductivity and thus ground heat flux, and the underestimation of the temperature in the deeper soil layers (e.g., soil temperature at 70-cm depth T s70 ; Fig.…”

“…(7) with c k 5 0 instead of Eq. (6) is due to its numerical efficiency (Niu and Yang 2006), as has been previously applied to Tibetan frozen soils (Bao et al 2016). The needed total soil water contents are estimated through linear interpolation between the liquid water contents measured before and after the freezethaw cycle as in Flerchinger et al (2006).…”

“…(6) is further replaced with Eq. (7) with c k 5 0 because of its numerical efficiency and suitability for Tibetan frozen soil (Bao et al 2016;Niu and Yang 2006), and the site-specific b l values given in section 3b are also implemented, while other settings are identical to EXP1. Specifically, the value of b l is specified as 3.5 for the first soil layer, and a value of 4.0 is assigned for other soil layers.…”

Development of a land surface model with coupled snow and frozen soil physics

“…In winter, the frozen soil occupies 55–60% of the land surface in the Northern Hemisphere [ Zhang et al ., ] and 72% of the Chinese territory [ Li et al ., ]. The reduction or expansion of permafrost, mainly contained in the high‐latitude or high‐altitude regions, is a key response to climate change at long time scales [ Kurylyk et al ., ; Bao et al ., ]. Permafrost thaw induced by rising subsurface temperatures will likely alter surface and subsurface hydrology in high‐altitude and/or latitude regions [ Kurylyk et al ., ].…”