Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 9/14/1999
Publication Date: N/A
Interpretive Summary: Temperature conditions in the near-surface soil environment drives many important plant and other biological processes, including plant germination and establishment, residue decomposition, insect population and soil freezing. Vegetation and residue cover, which can be controlled by management, affects the spatial and temporal variability of heat and water in the soil. Snow and frozen soil are key factors influencing the winter hydrology in many areas. Land managers need to address the interactions between physical, chemical and biological factors in the near surface, but lack the information necessary. The ability to predict temperature and water within the soil-plant-atmosphere system enhances our ability to evaluate management options and enables better understanding of interactions between surface processes and the atmosphere. The soil heat modules described in this chapter address previously identified development tneeds for the Root Zone Water Quality Model (RZWQM). Simplified snow routines enable over-winter simulation with the model. A developmental version with boundary conditions for soil heat transfer which make the model more responsive to varying management scenarios is described. This developmental version also includes provisions for frozen soil, which is critical in management of soil and water resources in northern latitudes.
Technical Abstract: Snow and soil heat modules described in this chapter address needs previously identified to improve soil temperature simulation and address wintertime phenomena of snow and frozen soils. Current and developmental heat and energy transfer equations for the RZWQM are described. The user may select an option with simplified surface boundary conditions and snow melt routines or a developmental option which computes a surface energy balance for soil heat transport and has detailed provisions for soil freezing and thawing. The simplified surface boundary conditions uses air temperature as the soil surface temperature for soil heat transport. Simplified winter routines use snow melt routines patterned after the Precipitation Runoff Modeling System (PRMS) and have no provisions for soil freezing. The developmental options of the model include detailed provisions for soil freezing and thawing patterned after the Simultaneous Heat and Water (SHAW) model. Surface boundary conditions for soil heat flux are computed differently depending on whether winter conditions exist. For winter conditions, heat flux at the soil surface is integrated with the physics of heat transfer through snow, residue and plant canopy layers similar to algorithms used in the SHAW model. A much simpler and computationally more efficient Penman-type algorithm (termed PENFLUX) is implemented for non-winter conditions. These algorithms are implemented as developmental options within RZWQM and are in the evaluation process, prior to release.