A physically based analytical model is formulated to simulate the thaw depth of active layer under changing boundary condition of soil heat flux. The energy conservation statement leads to a nonlinear integral equation of the thaw depth using an approximate temperature profile as an analytical solution of the diffusion equation describing the heat transfer in the active layer. The time-varying soil surface heat flux is estimated using non-gradient models when field observations are not available. The proposed model was validated against field observations at three Arctic forest and tundra sites. The simulated thaw depth and soil temperature profiles are in good agreement with observations hinting the potential for model application at larger spatial scales.

A physically based model is formulated for the active layer depth of permafrost under changing boundary condition instead of constant boundary condition considered in the traditional Stefan problem. Time varying ground heat flux is obtained from net radiation and surface temperature using the Maximum Entropy Production (MEP) model as the driver of the active layer melting process. Conductive heat flux at the melting front is approximated in terms of an analytical function of ground heat flux. The simulated active layer depth is in good agreement with the field observations.

The Calhoun Critical Zone Observatory (CCZO) has been collecting above and below canopy water, energy and carbon fluxes and other hydro-meteorological processes since 2016. The observations provide a unique opportunity to investigate the coupling between aboveground environmental conditions and belowground fluxes of mass and energy in general and the fate of fixed carbon in forested ecosystems in particular. The simultaneous measurements of soil-canopy-atmosphere states and fluxes reveal the role of pine forest in diurnal and seasonal dynamics of the CCZ ecosystem.