MODELING PLANT CANOPY EFFECTS ON VARIABILITY OF SOIL-TEMPERATURE AND WATER - MODEL CALIBRATION AND VALIDATION

Temperature conditions and the availability of moisture in the near-su rface soil environment drives many important plant and other biologica l processes. Vegetation, which can be controlled by management, affect s the spatial and temporal variability of heat and water in the soil. Land managers need to address the interactions between physical, chemi cal and biological factors in the near surface, but lack the necessary information. The ability to predict temperature and water within the soil-plant-atmosphere system enhances our ability to evaluate manageme nt options and enables better understanding of interactions between su rface processes and the atmosphere. The Simultaneous Heat and Water (S HAW) Model, a detailed model of heat and water movement in a plant-sno w-residue-soil system, was applied to 2 full years of data on semi-ari d sagebrush rangeland to simulate vegetation effects on the spatial an d temporal variation of soil temperature and water. Minor calibration was necessary to match the drop in measured soil water potential as th e soil dried in the late spring and early summer. The model accounted for over 93% of the variation in average daily soil temperature for a sagebrush-covered area and over 96% of the variation in temperature fo r a bare soil surface for 2 years. Rapid changes in surface water pote ntial and drying of the soil profile as simulated by the model closely tracked measured observations. (C) 1997 Academic Press Limited.