SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...
SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...
SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...
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Coupled water, vapor, and heat movement in the vadose zone is a central<br />
process in many agricultural and engineering issues (Saito et al., 2006).<br />
Especially, in cold and arid regions, snowmelt or lateral water movement on<br />
frozen soil layers have a non-negligible influence on seasonal water balances.<br />
Frozen soil normally reduces infiltration capacity dramatically due to the blocking<br />
effects of ice lenses in soil pores. Consequently, lateral flow and snow melt may<br />
release huge quantities of water in spring and early summer, and cause<br />
substantial surface runoff (Lewkowicz and Kokelj, 2002; Bayard, et al., 2005).<br />
Furthermore, this will increase the risk for soil erosion and nutrient loss. However,<br />
although the former processes are recognized widely, the simulations of snow<br />
hydrology and soil freezing and thawing are rarely done due to limited data<br />
availability to parameterize or validate such models and lack of suitable models<br />
that describe the complex processes during phase changes.<br />
Generally, frozen soils are characterized by the coexistence of ice and water.<br />
Thus it is necessary to simulate the freezing and thawing process by specifically<br />
considering the phase change of ice and water at variable freezing points. Over<br />
the last few decades, two prevalent classes of soil freezing and thawing models,<br />
namely hydrodynamic models (e.g., Harlan, 1973; Flerchinger and Saxton, 1989)<br />
and frost heave models (e.g., Miller, 1980) have been developed. They mainly<br />
differed in the treatment of ice pressure, which is assumed to remain constant in<br />
hydrodynamic models and variable in the frost heave models (Hansson et al.,<br />
2004). As a result, the former offers accurate predictions <strong>und</strong>er saturated<br />
conditions but limits to frost heave, which is reverse for the latter. Regarding the<br />
model’s availability in the unsaturated zone, it is customary to use the<br />
hydrodynamic model in soil science.<br />
Generally, water and energy balances are linked at the soil-atmosphere<br />
interface and controlled by climatic conditions and soil properties. In winter,<br />
snow cover results in low thermal conductivity and high albedo of soil surface,<br />
which greatly impacts soil thermal regime and microclimate. Within the soil,<br />
thermal gradient induces moisture transfer which, in turn, affects heat flow.<br />
Furthermore, soil heat and water regimes may be modified by different land uses<br />
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