Coupled Snow and Frozen Ground Physics Improves Cold Region Hydrological Simulations: An Evaluation at the upper Yangtze River Basin (Tibetan Plateau)

Abstract

Cryosphere plays an important role in cold‐region (e.g., Tibetan Plateau) hydrological processes under climate change, and thus cryosphere physics should be carefully represented in the hydrological modeling. In this study, based on the Water and Energy Budget‐based Distributed Hydrological Model (WEB‐DHM), we have further improved the cold‐region hydrological processes, by incorporating the enthalpy‐based coupled snow and frozen ground physics (hereinafter WEB‐DHM‐SF), and comprehensively evaluated at the upper Yangtze River Basin under widespread snow cover and frozen ground. The model was calibrated and validated at the basin scale using observed discharge at Zhimenda station during 1981–2016 and simulated discharge with high accuracies. The model also successfully reproduced the basin‐wide daytime and nighttime land surface temperature (LST) as well as snow depth in basin‐averaged time series and spatial distributions. At the point scale, the model successfully reproduced soil moisture and temperature profiles at Tuotuohe based on available yearlong observations. Furthermore, experiments were designed to investigate model improvements and indicated that the incorporation of the three‐layer snow scheme with correct consideration of incident solar radiation attenuation among snow layers resulted in lowered snow melting and reduced discharges. Additionally, the incorporation of frozen ground physics with a correct description of soil water phase changes rendered the modeled soil moistures and temperatures more accurate in the cold season. Through rigorous evaluations of model performance, the incorporation of coupled snow and frozen ground physics demonstrates significant promise for improving cryosphere hydrological simulations in river basins on the TP.

Improving Permafrost Physics in a Distributed Cryosphere‐Hydrology Model and Its Evaluations at the Upper Yellow River Basin

“…For improved cryosphere-hydrology simulation, the WEB-DHM is further physically enhanced with the enthalpy-based snow and frozen soil processes (Shrestha et al, 2010;Wang, Zhou, et al, 2017), implemented using the three-layer energy-balance snow parameterization from SSiB3 (Sun et al, 1999;Sun & Xue, 2001) and frozen soil parameterization based on enthalpy theory (Li & Sun, 2008). This model can efficiently simulate freeze-thaw processes at the point scale (e.g., Wang, Zhou, et al, 2017) and hydrological processes in large-scale river basins while incorporating subgrid topography (e.g., Qi et al, 2019). In this study, a new version of the WEB-DHM has been developed by formulating the water and heat exchanges between the unconfined aquifer and its upper soil layers in a permafrost region (hereinafter WEB-DHM-pf; Figure 1).…”

“…Zhang et al (2016); Zhang, Chang, & Liang, 2017; Zhang et al, 2018), and Sun et al (2019) highlighted the influences of topographic shadows in areas with rugged terrain and deep valleys by applying SHAWDHM (Simultaneous Heat and Water Distributed Hydrological Model) and WaSiM (Water Balance Simulation Model), respectively. In recent years, the WEB‐DHM model (Water and Energy Budget‐based Distributed Hydrological Model) has been coupled with an enthalpy‐based three‐layer snow module and frozen soil module (Qi et al, 2019; Wang, Zhou, et al, 2017). The model can reasonably describe the physical processes of multisphere interactions (including cryosphere, hydrosphere, biosphere, and atmosphere) and has shown good applications in the cryosphere regions of the QTP, such as Ngari Station and DY Station (Wang, Zhou, et al, 2017) and in the upper Yangtze River basin (Qi et al, 2019).…”

Understanding the mass, momentum, and energy transfer in the frozen soil with three levels of model complexities

“…Second, the fully coupled water and heat physics, i.e., water vapor flow and thermal effect on water flow, was explicitly considered in STEMMUS and termed the advanced coupled model (ACM). For the ACM physics, the extended version of the Richards (1931) equation, with modifications made by Milly (1982), was used as the water conservation equation (Eq. 3).…”

Snow as an Important Natural Reservoir for Runoff and Soil Moisture in Northeast China

“…The snowmelt is calculated based on water and energy balances in snow layers. The snowmelt module uses a three-layer snowmelt simulation approach from the Simplified Simple Biosphere 3 (SSiB3) and the Biosphere-Atmosphere Transfer Scheme (BATS) albedo scheme (Qi, Wang, et al, 2019;Shrestha et al, 2010Shrestha et al, , 2015. This model…”