A general method of parameterizing the big‐leaf model to predict the dry‐canopy evaporation rate of individual coniferous forest stands

Abstract

Abstract:This study proposes a general method of parameterizing the big-leaf model that is applicable to estimation of daytime dry-canopy evaporation (hereafter, evaporation) rates of coniferous forest stands without observed flux data. The method considers variation in the reference value of surface conductance G s between individual stands by incorporating a relationship between canopy height and reference G s values reported by Komatsu (2003c) [Hydrological Processes 17: 2503-2512. However, the method does not consider variation in modifier functions of G s and in aerodynamic conductance G a between individual stands.We examined the validity of the method based on daytime evaporation rate data for 26 coniferous stands. The method showed greater predictability than another method that ignores variation in reference G s values between individual stands. This illustrates the validity of considering variation in reference G s values between individual stands. Model predictability was not enhanced by considering variation in modifier functions of G s and G a between individual stands. This illustrates the validity of ignoring variation in modifier functions of G s and G a between individual stands.The method is applicable to stands with projected LAI ½ 3Ð0 and canopy height <c. 30 m. The method can result in errors when applied outside these limitations. Regardless, the method should be valuable for estimating daytime evaporation rates of coniferous stands, as many stands fall within these limitations. The method is applicable to evaporation rate estimates in growing seasons without soil water stress when dry-canopy evaporation significantly affects the forest water cycle. At this stage, the method can result in errors when applied outside this limitation. However, the method should be valuable as a basis for developing a more comprehensive method applicable outside this limitation.

Contemporary Role of Catchment Water Balance Data for Forest Evapotranspiration Research.

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Changes in canopy transpiration due to thinning of a Cryptomeria japonica plantation

“…However, we presume that this increase would not be considerable. Variations in the relationship between S and G c cause slight differences in E for forests at daily or longer time-scales (Komatsu, 2004). Indeed, most studies examining changes in E due to thinning at these scales did not observe evidence of an increase in E due to the improved light-environment by thinning (Whitehead and Kelliher, 1991;Lagergren et al, 2008).…”

A simple model to estimate monthly forest evapotranspiration in Japan from monthly temperature

“…Forest evapotranspiration usually depends on vapour pressure deficit rather than incident radiation because forest canopies are aerodynamically rough (McNaughton and Black, 1973;Jarvis and McNaughton, 1986;Komatsu, 2003Komatsu, , 2004. Despite this, assuming that E / E eq is reasonable because the vapour pressure deficit relates to incident radiation due to planetary boundary layer feedback (De Bruin, 1983;McNaughton, 1989;Raupach, 1998).…”