Using field observations to inform thermal hydrology models of permafrost dynamics with ATS (v0.83)

Abstract

Abstract. Climate change is profoundly transforming the carbon-rich Arctic tundra landscape, potentially moving it from a carbon sink to a carbon source by increasing the thickness of soil that thaws on a seasonal basis. However, the modeling capability and precise parameterizations of the physical characteristics needed to estimate projected active layer thickness (ALT) are limited in Earth system models (ESMs). In particular, discrepancies in spatial scale between field measurements and Earth system models challenge validation and parameterization of hydrothermal models. A recently developed surface-subsurface model for permafrost thermal hydrology, the Advanced Terrestrial Simulator (ATS), is used in combination with field measurements to achieve the goals of constructing a process-rich model based on plausible parameters and to identify fine-scale controls of ALT in ice-wedge polygon tundra in Barrow, Alaska. An iterative model refinement procedure that cycles between borehole temperature and snow cover measurements and simulations functions to evaluate and parameterize different model processes necessary to simulate freeze-thaw processes and ALT formation. After model refinement and calibration, reasonable matches between simulated and measured soil temperatures are obtained, with the largest errors occurring during early summer above ice wedges (e.g., troughs). The results suggest that properly constructed and calibrated onedimensional thermal hydrology models have the potential to provide reasonable representation of the subsurface thermal response and can be used to infer model input parameters and process representations. The models for soil thermal conductivity and snow distribution were found to be the most sensitive process representations. However, information on lateral flow and snowpack evolution might be needed to constrain model representations of surface hydrology and snow depth.

Impacts of microtopographic snow redistribution and lateral subsurface processes on hydrologic and thermal states in an Arctic polygonal ground ecosystem: a case study using ELM-3D v1.0

“…Three recent studies have used other mechanistic models to simulate soil temperature fields at this site and achieved comparably good comparisons with observations (Kumar et al, 2016 applied a 3-D version of PFLOTRAN; Atchley et al, 2015 andHarp et al, 2016 applied a 1-D version of the Arctic Terrestrial Simulator -ATS). However, those models used measured soil temperatures near the surface as the top boundary condition.…”

Modeling the spatiotemporal variability in subsurface thermal regimes across a low-relief polygonal tundra landscape

“…Atchley et al (2015) and Harp et al (2016) have successfully demonstrated the use of such techniques for three-phase hydrology models at one of our sites (site C) and would inform our future studies.…”

“…Figure 3 illustrates the subsurface soil horizons based on observations that we used in all our modeling studies presented here. In absence of colocated observations for soil hydraulic and thermal properties we derived the data for use in our studies from the published literature in tundra regions (Hinzman et al, 1991(Hinzman et al, , 1998) and a recent parameter calibration study conducted at one of our sites (Site C) (Atchley et al, 2015). Table D1 shows the soil hydraulic and thermal properties used in our modeling study.…”

Water flow in the active layer along an arctic slope – An investigation based on a field campaign and model simulations

“…Thus the flow velocity is variable in three dimensions: Vertical variations in the velocity are caused not only by variations in porosity and permeability over depth (Quinton et al, 2008), humification (Letts et al, 2000) and diplotelmic flow (Jessen et al, 2014) but are also related to the existence of a saturated layer at the bottom of the active layer. Lateral alterations of the velocity arise due to a network of water paths that is controlled by the micro-topography of the permafrost table (Atchley et al, 2015). 5…”

“…The microtopograhpy of the frost table creates a complicated flow networks that also lead to lateral flow (Atchley et al, 2015). Models capable of simulating the complex mechanisms occurring in cold climate environment have only recently emerged (Kurylyk et al, 2014) and are still 15 under development.…”