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

Abstract

Snow and frozen soil are important factors that influence terrestrial water and energy balances through snowpack accumulation and melt and soil freeze-thaw. In this study, a new land surface model (LSM) with coupled snow and frozen soil physics was developed based on a hydrologically improved LSM (HydroSiB2). First, an energy-balance-based three-layer snow model was incorporated into HydroSiB2 (hereafter HydroSiB2-S) to provide an improved description of the internal processes of the snow pack. Second, a universal and simplified soil model was coupled with HydroSiB2-S to depict soil water freezing and thawing (hereafter HydroSiB2-SF). In order to avoid the instability caused by the uncertainty in estimating water phase changes, enthalpy was adopted as a prognostic variable instead of snow/soil temperature in the energy balance equation of the snow/frozen soil module. The newly developed models were then carefully evaluated at two typical sites of the Tibetan Plateau (TP) (one snow covered and the other snow free, both with underlying frozen soil). At the snow-covered site in northeastern TP (DY), HydroSiB2-SF demonstrated significant improvements over HydroSiB2-F (same as HydroSiB2-SF but using the original single-layer snow module of HydroSiB2), showing the importance of snow internal processes in three-layer snow parameterization. At the snow-free site in southwestern TP (Ngari), HydroSiB2-SF reasonably simulated soil water phase changes while HydroSiB2-S did not, indicating the crucial role of frozen soil parameterization in depicting the soil thermal and water dynamics. Finally, HydroSiB2-SF proved to be capable of simulating upward moisture fluxes toward the freezing front from the underlying soil layers in winter.

Liquid‐Vapor‐Air Flow in the Frozen Soil

“…Journal of Geophysical Research: Atmospheres Note that the effect of snow accumulation and ablation was not considered in the current version of STEMMUS-FT model. In our further development of the model, we will incorporate such effect in a more realistic and physical way (e.g., Boone & Etchevers, 2001;Ding et al, 2017;Koren et al, 1999;Tarboton & Luce, 1996;Wang et al, 2017).…”

Improved Simulation of Frozen‐Thawing Process in Land Surface Model (CLM4.5)

“…Enhancements in the parameterization of soil water and heat transport in LSM have greatly improved the simulation of terrestrial hydrological cycles and surface energy balances in cold regions (Bao et al, ; Cuo et al, ; Hu et al, ; Lawrence et al, ; Wang et al, ). However, LSM still provides inadequate simulations at high latitudes and areas of complex topography.…”

The Improved Freeze–Thaw Process of a Climate‐Vegetation Model: Calibration and Validation Tests in the Source Region of the Yellow River

“…However, many studies pointed out that if snow accumulation was substantial, the snow has impacts on the freeze–thaw process. For example, Wang et al () used a complex snow parameterization scheme combined with a frozen soil model to improve the model simulation performance and noted that snow cover had a significant impact on shortwave radiation attenuation and surface energy balance, which may affect freeze–thaw process simulation. Slater et al () noted that the snow albedo, cover ratio, evaporation, and especially the way that the snow layer and topsoil layer were connected, all affected the freeze–thaw process simulation.…”