In support of the overall scientific objective of the Boreal Ecosystem-Atmosphere Study (BOREAS), which encompasses the improved understanding of the interactions between the boreal forest and the atmosphere, a process-based water and energy balance model is applied to observed forcing data, and the results are presented and discussed. Observed tower forcing and validation data are analyzed. A consistent diurnal pattern in the energy balance closure of the validation data is obtained. Simulations are performed for a number of BOREAS flux tower sites. The model successfully simulates the temporally averaged Bowen ratio and the evaporative part of precipitation over the different BOREAS flux tower sites during the 1994 and 1996 intensive field campaigns. At finer temporal scales a small phase shift in sensible heat flux and net radiation exists between the observed and model-derived quantities. The ground heat flux is found to be slightly larger than the observations during the course of the day. It is suggested that the sensitivity of the model to parameters such as the moss thickness, thermal conductivity, and heat capacity is responsible for these differences. The moss moisture content and the different components of the energy balance were very well matched for a continuous simulation during 1996. Overall, the accuracy performance of the model is equivalent to the accuracy of the input forcing data. ¿ 1999 American Geophysical Union