A study on the Penman's potential evapotranspiration and the real evapotranspiration

• Published in: Research Reports of Kochi University. Agriculture (Japan) Vol. 51
• Main Authors: Kuroda, N.(Okayama Univ. (Japan)), Kamii, Y, Miura, T
• Format: Journal Article
• Language: Japanese
• Published: 01.12.2002
• Subjects: BALANCE HIDRICO; BILAN HYDRIQUE; CICLO HIDROLOGICO; CYCLE HYDROLOGIQUE; EVAPOTRANSPIRACION; EVAPOTRANSPIRATION; GRASSLANDS; HERBAGE; HYDROLOGICAL CYCLE; LOSSES FROM SOIL; PERDIDAS DESDE SUELOS; PERTE PAR LE SOL; PRADERAS; WATER BALANCE
• ISSN: 0389-0473

Evapotranspiration was studied by Heat Balance Bowen's Ratio Method on grassland of Faculty of Agriculture, Kochi University from December 27, 2001 to January 24, 2002. By simple and multiple regressional analyses, the following relationships are gotten. Y = 0.077 + 0.313X (rE2 = 0.894,s = 0.183,n = 29) where, Y : evapotranspiration (mm/d) , X : net radiation (MJ/mE2/d). Y = 0.241 + 0.152 X (rE2= 0.875,s = O.198, n = 29) where, Y : evapotranspiration (mm/d), X : global solar radiation (MJ/mE2/d). Y = -0.828 + 0.162X1 + 0.189X2+ 0.0107X3= (RE2 = 0.902, s = 0.182, n=29) where, Y : evapotranspiration (mm/d), X1 : global solar radiation (MJ/mE2/d), X2:daily mean wind velocity at 3.5m above the ground(hereafter, referred as the daily mean wind velocity, m/s), X, : daily mean relative humidity as the mean of 3m and 1m above the ground(hereafter, referred as the daily mean relative humidity, %). Y = - 2.25 + 0.512 X1 + 0.0127 X2 + 0.0261 X3 + 0.516 X4 + (RE2= 0.989, s = 0.190, n = 29) where, Y : evapotranspiration (mm/d), XE1 : global solar radiation (MJ/mE2/d), X2': daily mean temperature as the mean of 3m and 1m above the ground (hereafter, simply referred as the daily mean temperature (deg C), X3 : daily mean wind velocity (m/s) , X4 : daily mean relative humidity (%) . Y= -2.43 + 0.413 X1 -0.0843 X= + 0.0393 X3, + l.33 X4(RE2 = 0.992, s =0.164, n = 29) where, Y : evapotranspiration (mm/d) , X, : global solar radiation (MJ/mE2/d), X, : daily mean temperature (deg C), X3, : daily mean wind velocity (m/s) , X4 : Penman's daily potential evapotranspiration at 3m above the ground(mm/d). Y= 0.55 + 0.483 X(rE2=0. 968, s=0. 304, n=29) where, Y : net radiation (MJ/mE2/d), X: global solar, radiation (MJ/mE2/d). Y= 1.68 + 0.191 X1 +0.0722 X2-0.0286 X3+ 0.308 X4 (RE2=0.994, s=0.0592, n=29) where, Y:Penman's daytime potential evapotranspiration at 3m above the ground (mm/d), daytime : the hours while the net radiation is positive, X1 : net radiation (MJ/mE2/d), X2 : daytime mean temperature at the height of 3 m above the ground (deg C ), X3 : daytime mean relative humidity at the height of 3m above the ground(%) , X4 : daytime mean wind velocity (m/s). By using the class A pan and 20cm diameter pan, pan evaporations were studied at the other grassland of the campus at noon from October 1, 2001 to January 24, 2002. The relationship is expressed by the following formula. Y = 0.9672 X (s=1.016, n=116) where, Y : pan evaporation of class A pan measured (mm/d), X : pan evaporation of 20cm diameter pan measured (mm/d). : The above coefficient 0.9672 is far from those of passed studies' 0.6 to 0.8. The cause is not clear yet.