This poster describes strategies for modifying the VIC-2L to model frozen soil hydrologic processes in the Upper Mississippi basin. These include refinements to the snow accumulation and ablation algorithm, and explicit modeling of the effect of frozen soils on infiltration and runoff response. The result will be a new subsurface temperature and infiltration algorithm, that will be tested using surface radiation and heat flux data, as well as soil temperature and moisture profiles from the Rosemount Agricultural Station in Minnesota. Precipitation and temperature data were taken from NCDC cooperator stations, with other surface meteorological data interpolated from NCDC Surface Airways stations. Preliminary comparisons between data collected at the Rosemount site, and simulations using the SHAW model, are presented.
Frozen soils decrease the amount of infiltration, especially when ice content is high.
Snow accumulation occurs only when the soil surface is frozen. Snow packs last longest when deep frozen soils prevent melting from below. For the VIC-2L model, a numerical method was selected that solves for temperature at various levels within the soil. This allows the model to represent the sub-grid spatial variation of infiltration within a large grid cell. The freezing depth is calculated by computing soil temperatures at various soil depths, see Figure 3 .