Soil thermal and moisture regime beneath forest canopy: A coupled modeling approach

The interaction between water, vapor, and heat transport in soils plays a pivotal
role in regulating soil moisture and thermal regimes in forest ecosystems, yet
these processes are often modeled independently. Such approach may overlook
their inter-dependent dynamics, particularly under forest canopies where inter-
ception, evaporation, and energy exchange are strongly correlated. In this study,
a physics-based canopy interception model was developed and calibrated using
throughfall monitoring data from the AMALIA experimental site in central Bo-
hemia. The simulated intercepted rainfall is subsequently used as an upper
boundary condition for the Saito–Sakai model which couples the transport of
water, vapor, and heat in the soil profile. Surface energy balance was applied
as the thermal boundary condition, accounting for coupled heat and vapor ex-
change, while precipitation served as the moisture flux boundary. The model
was calibrated and validated against month-long soil temperature and moisture
measurements across three soil horizons, with meteorological forcing derived
from ERA5-Land hourly reanalysis data interpolated to match the observational
time step. Model performance demonstrated good agreement with observations,
successfully reproducing soil temperature and moisture dynamics beneath the
forest canopy and highlighted the importance of interception-induced delays of
rainfall inputs. Results demonstrate that neglecting canopy–soil interactions
can lead to biased estimates of near-surface soil states, particularly during wet-
ting and drying events. The proposed approach provides a physically consistent
link between canopy processes and subsurface thermal–hydrological dynamics
and can improve the representation of forest soil conditions in land-surface and
ecohydrological models.