PREDICTING FOREST SOIL TEMPERATURES FROM MONTHLY AIR-TEMPERATURE AND PRECIPITATION RECORDS

A process-oriented forest soil temperature model, FORSTEM, is presente d. FORSTEM considers vertical heat conduction as well as freezing and thawing, and it lumps the effects of forest canopies on soil surface t emperature with the surface heat transfer coefficient. It runs in conj unction with the forest hydrologic model, FORHYM. FORSTEM and FORHYM i nput is limited to (i) air temperature; (ii) precipitation and its sno w fraction; and (iii) descriptive site information (latitude, elevatio n, slope, aspect, forest coverage, and soil layer thickness and textur e). FORSTEM uses generalized parameters derived from existing empirica l information. The model was applied to 10 different cover type - site conditions, including lawns, deciduous forests, and coniferous forest s before and after clear-cutting in Ontario, Quebec, New Brunswick, an d Colorado. The only model parameter we calibrated for different sites was the effective ground/air conductance ratio. The ratio was found t o be a function of incoming solar radiation and vegetative area index. Differences between monthly simulations and field measurements fell w ithin +/-1.5 degrees C for at least about three-quarters of the data c ases at individual sites. Major exceptions occurred when temperature m easurements showed no damping down the soil profile or with soils cont aining large air gaps between coarse rock fragments.