Estimating forest evapotranspiration at a non-ideal site

Abstract

Evapotranspiration estimates by a Bowen ratio energy balance system and an eddy correlation energy balance system taken simultaneously at a tall coniferous forest site on sloping terrain with inadequate fetch are analyzed. The analysis of the results of both measurement systems reveals significant differences between the two. For most data points the Bowen ratio technique led to lower rates of evapotranspiration when compared with the eddy correlation results. These differences are attributed to measurement errors, to the violation of theoretical requirements, and to site specifics. Especially fetch requirements were smaller for the Bowen ratio system than for the eddy correlation system suggesting a different source area for the two techniques used. The analysis demonstrates that caution is required, when applying micrometeorological methods to non-ideal sites.