Model for Annual Water and Energy Flow in a Layered Soil

Abstract

The SOIL model describes the abiotic processes during the whole year in a glacifluvial sandy forest soil at Jadras, central Sweden. It incorporates interception, snow accumulation and melt, and ground water percolation to give appropriate boundary conditions to the soil. Self-sustained modules for different parts of the system are connected through the main program. This program structure makes it possible to study each process separately, to incorporate various degrees of interactions, and to directly compare different theories for the separate processes. Required driving variables are daily totals of potential transpiration, precipitation, global radiation, and a daily mean of air temperature. The model yields profiles of temperature, thermal quality (frost), volumetric water content, water potential, energy and water flux. Simulation results for three winters with intervening summers indicate that the simple snow module may be improved. Annual temperature and frost are sensitive to snow cover as also are infiltration and percolation. Both the dry 1976 and the wet 1977 summers show good agreement between measured and simulated temperatures and water status. The most sensitive parameter is the surface resistance, which cannot be estimated independently. The model can thus not presently be applied successfully to another site without previous measurements of soil water status. Additional index words: Evaporation, forest soil, frost, infiltration, matric potential, root water uptake, snow, soil temperature, thermal conductivity, transpiration, unsaturated conductivity, water content.