MODELING VERTICAL AND LATERAL WATER-FLOW IN FROZEN AND SLOPED FOREST SOIL PLOTS

Snowmelt runoff from forest land is influenced by the spatial distribu tion of soil frost which depends on climatic conditions and stand stru cture. Snow and frost dynamics as well as near-surface runoff and liqu id water content in the soil were measured for two years in two small plots located on a slope within a subalpine spruce stand. These measur ements were used to calibrate the one-dimensional water and heat trans port model SOIL by only fitting three snow- and two soil-related param eters. The simulated snow and frost dynamics agreed well with field da ta. The partitioning of snowmelt water into lateral runoff and vertica l percolation at the snowpack bottom was best represented assuming tha t downward water flow through the frozen layers occurred not only in t he liquid phase between soil particles and pore ice (low-flow-domain) but also as microscopic bypass flow in the previously air-filled macro pores (high-flow-domain). Simulated near-surface runoff is very sensit ive to the impedance factor accounting for a reduced upward water flow in frozen soil layers and also to the heat transfer coefficient contr olling the refreezing of water infiltrating through the empty voids. T he runoff dynamics differed only slightly when the model was driven by daily instead of hourly weather variables. (C) 1997 Elsevier Science B.V.