Estimation of Sensible and Latent Heat Fluxes of an Isolated Tree in Japanese Summer
2020
Asawa, Takashi | Fujiwara, Kunihiko
Considering that the characteristics of the heat balance between an isolated tree and the urban atmosphere have not yet been sufficiently clarified, we quantify both the sensible heat flux ([Formula: see text]) and latent heat flux ([Formula: see text]) to and from an isolated Z. Serrata in the Japanese summer. To estimate the whole-tree transpiration rate (ET) and [Formula: see text] values, we apply a previously developed method using a weighing lysimeter. To estimate the boundary-layer heat conductance ([Formula: see text]) of the total leaf area of the tree crown and the sensible heat flux ([Formula: see text]), we apply a scaling-up approach using the heat-balance two-state (HB-TS) method, which previously only targeted single leaves, to the tree crown. Two sample trees with similar crown shape and total leaf area are selected for the HB-TS method but under different irrigation conditions, and [Formula: see text] is estimated. The ET values of the tree change three times during the dry-down experiment (during which time irrigation was halted). We also compare HT and lET values between two different days under different irrigation and soil–water conditions. The most important result from this comparison is that the tendencies of HT and lET were reversed on these days, and the Bowen ratio ([Formula: see text]) dramatically varies between 0.29 and 2.2. These results indicate that the Bowen ratio of isolated trees at urban sites can vary between the previously reported values for forest sites and those for artificial urban sites within a short period, owing to urban-unique conditions (e.g., limited water supply and rooting space, and artificial sealing).
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