Abstract
The evapotranspiration rate was calculated by Thornthwaite-Holzman model from the data obtained in a deciduous broad-leaved secondary forest in Yamashiro Town, Sohraku Country, Kyoto Prefecture. The parameters showing the effectiveness of sensible heat exchange in this model were estimated to be 0.12 in a foriaged season and 0.077 in a defoliated season, i.e. the former is 1.5 times as high as the latter. The maximum daily rate of evapotranspiration was stable and estimated to be about 12MJ/(m2·day) in a foliaged season. On the other hand, those calculated in a defoliated season varied widely from about 2MJ/(m2·day) in January to 6-7MJ/ (m2·day) in November and April. In comparison of the result calculated by Thornthwaite-Holzman model with that introduced by Bowen ratio method, it was revealed that Thornthwaite-Holzman model is able to estimate more accurately in a defoliated season, and give no less accurate estimate in a foliaged season than Bowen ratio method does. The ratios of evapotranspiration against effective radiation were estimated to be about 40% from January to April and about 60% from June to November. The increase of this ratio delayed about one month from a leafing time. Moreover, these ratios were almost equal to those in a Japanese Hinoki forest and a Swedish pine forest, although there were differences in a seasonal variations.
