水田の蒸発散

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書誌事項

タイトル別名
  • Evapotranspiration from Paddy Field
  • スイデン ノ ジョウハッサン
公開日
1967
DOI
  • 10.2480/agrmet.22.149
公開者
日本農業気象学会

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説明

During the growing season (June 26 to Oct. 6, 1965) of rice plants, as part of a wide-ranging study of problems on water balance in river basins, the N.I.A.S. Division of Meteorology made measurements of meteorological elements in the surface air layer over a paddy field at Konosu, Saitama, in order to estimate the evapotranspiration from a paddy field. The data are first summarized in hourly mean and hourly total values. The evapotranspiration was estimated by processing the data by heat balance, combination and gradient (bulk) methods. respectively.<br>The radiative dry index (=ΣS/Σlr) for the period of rice growing was found to be 0.89, implying that the climatic condition during the growing season was rather humid. The ratio of total evapotranspiration to total rain fall evaluated from the value of radiative dry index was 0.72 and was in accordance with the measured value (0.73). The total evapotranspiration from the paddy field was respectively estimated as 309mm by heat balance method, 347mm combination method and 317mm bulk method. These values were smaller than the total evaporation (379mm) measured by a small evaporimeter (diameter, 20cm) in a near enclosure. The net radiant equivalent (=ΣS/l, 378mm) was in good agreement with the pan evaporation.<br>Mean value of the ratio (=ΣET/ΣEp; ET, evapotranspiration by heat balance method; Ep, pan evaporation) was found to be 0.82 and to be somewhat small comparing with those (1.0-1.2) reported by several researchers. Our result indicates that, for the growing period of rice plants, (1+β) is constantly larger than 1.0 and that there is a some sensible heat loss. Dependence of evapotranspiration (ET) on net radiant equivalent (S*=S/l) was approximated by<br>ET=0.82S*.<br>The value of a proportional constant was in accordance with those obtained at irrigated ryegrass fields and paddy fields. This seems to indicate that the adverted heat does not contribute a significant part of the latent heat used in evapotranspiration from wide paddy fields under moist climatic conditions like summer in Japan. The following relation was obtained between Ec (evapotranspiration estimated by combination method) and ET:<br>ET=0.92EC.<br>The difference between ET and EC may be due to not taking into account the effect of dryness of the plant canopy on evaportanspiration in the calculation.<br>It can be concluded from results presented above that the heat balance method and the combination method are suitable for estimating evapotranspiration from paddy fields. However, it is much desirable to compare evapotranspiration estimated by these methods with that determined directrly by lysimeters or an evapotron.

収録刊行物

  • 農業気象

    農業気象 22 (4), 149-157, 1967

    日本農業気象学会

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