Modeling Aspect‐Controlled Evolution of Ground Thermal Regimes on Montane Hillslopes

Abstract

The thermal and hydrologic state of the ground controls a wide range of environmental processes in high elevation regions. For example, the seasonal evolution of soil temperature and moisture restricts the microbial and plant populations that may occupy the soil and their associated contributions to carbon and nitrogen cycles (Brooks et al., 1997;Donhauser & Frey, 2018). Soil ice formation contributes to downslope soil migration and influences the ability of liquid water to infiltrate (Matsuoka, 2001;Walvoord & Kurylyk, 2016). In seasonally snow-covered environments, the snowpack acts as an insulator, dampening the propagation of surface energy balance changes into the subsurface. In light of anticipated changes in air temperature and precipitation throughout high elevation regions, including higher winter precipitation, lower summer precipitation, and generally higher temperatures throughout the year (Liu et al., 2017), there is a need for process-based models that characterize the seasonal evolution of soil temperature and moisture as a step toward quantifying watershed-scale changes in hydrology, biogeochemistry, and geomorphology. While the models developed in this study are designed to reproduce annual soil temperature cycles, particular focus is given to the occurrence of frozen ground, which acts as a critical threshold for hydrologic, geomorphological, and biogeochemical processes in mountain environments.Hydrology and infiltration are influenced by seasonally frozen ground (SFG) (Hayashi, 2013). In contrast to permafrost, which remains at or below 0°C for at least 2 years, SFG freezes and thaws annually (Harris et al., 1988). Hydraulic conductivity decreases by orders of magnitude during the transition from unfrozen to frozen ground (

The Role of Groundwater Flow in a Montane, Semi-Arid, Headwater Catchment

“…Although slope aspect is not expressly addressed in this study, it is acknowledged that this may be a critical mechanism driving differences in groundwater recharge in the catchment (e.g., Hinckley et al, 2014;2017;Langston et al, 2015;Rush et al, 2021). Differences in the annual precipitation, snow depth and duration, and evapotranspiration rates across the north-and south-facing slopes are apparent in field data and discussed in detail in Supporting Information.…”

“…On the north-facing slopes, vegetation is dense and populated by lodgepole pine (Pinus contorta ); south-facing slopes are less vegetated and populated by shrubs, grasses and a scattering of ponderosa pine trees (Pinus ponderosa ) (Adams et al, 2014). In the northern hemisphere, south-facing slopes intercept a greater amount of solar, shortwave radiation than the north-facing slopes (Fan et al, 2019), resulting in thinner snowpacks with multiple cycles of snow accumulation and melt Rush et al, 2021). Conversely, the north-facing slopes retain a snowpack from the late fall through spring and experience more pervasive frost due to the colder temperatures (Rush et al, 2021).…”

“…In the northern hemisphere, south-facing slopes intercept a greater amount of solar, shortwave radiation than the north-facing slopes (Fan et al, 2019), resulting in thinner snowpacks with multiple cycles of snow accumulation and melt Rush et al, 2021). Conversely, the north-facing slopes retain a snowpack from the late fall through spring and experience more pervasive frost due to the colder temperatures (Rush et al, 2021). In addition to greater thickness of weathered rock and saprolite on north-facing slopes (Befus et al, 2011), the saprolite is more porous and granulated than on south-facing slopes, where it is more intact and fractured (Bandler, 2016).…”

Influence of Snowpack Cold Content on Seasonally Frozen Ground and Its Hydrologic Consequences: A Case Study From Niwot Ridge, CO

“…RUSH AND RAJARAM 10.1029/2021WR031911 4 of 28 In this study, the coupled model developed in Rush et al (2021) is used to simulate seasonal soil freezing at Niwot Ridge and its hydrologic consequences. The model consists of surface energy balance estimates and a physical snowpack model that are used to produce ground surface temperatures and infiltration rates as boundary conditions for a subsurface thermo-hydrologic model at an hourly timestep.…”

“…(2004), and Rush et al. (2021), and is summarized briefly in this section. It is generally understood that snowcover acts to decouple the soil from the atmosphere due to snow's low thermal conductivity, high latent heat of fusion, and high albedo (Zhang, 2005).…”