Abstract. The vadose zone is a zone sensitive to environmental
changes and exerts a crucial control in ecosystem functioning and even more
so in cold regions considering the rapid change in seasonally frozen ground
under climate warming. While the way in representing the underlying physical
process of the vadose zone differs among models, the effect of such differences
on ecosystem functioning and its ecohydrological response to freeze–thaw
cycles are seldom reported. Here, the detailed vadose zone process model
STEMMUS (Simultaneous Transfer of Energy, Mass
and Momentum in Unsaturated Soil) was coupled with the ecohydrological model Tethys–Chloris (T&C) to investigate the
role of influential physical processes during freeze–thaw cycles. The
physical representation is increased from using T&C coupling without STEMMUS enabling the
simultaneous mass and energy transfer in the soil system (liquid, vapor,
ice) – and with
explicit consideration of the impact of soil ice content on energy and water
transfer properties – to using T&C coupling with it. We tested model performance with the aid of a comprehensive
observation dataset collected at a typical meadow ecosystem on the Tibetan
Plateau. Results indicated that (i) explicitly considering the frozen soil
process significantly improved the soil moisture/temperature profile
simulations and facilitated our understanding of the water transfer
processes within the soil–plant–atmosphere continuum; (ii) the difference
among various representations of vadose zone physics have an impact on the
vegetation dynamics mainly at the beginning of the growing season; and (iii) models with different vadose zone physics can predict similar interannual
vegetation dynamics, as well as energy, water, and carbon exchanges, at the land
surface. This research highlights the important role of vadose zone physics
for ecosystem functioning in cold regions and can support the development
and application of future Earth system models.
Cryoprotectin: a plant lipid–transfer protein homologue that stabilizes membranes during freezing
