Master's Dissertation
DOI
10.11606/D.11.2002.tde-16052002-095603
Document
Author
Full name
Alailson Venceslau Santiago
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 2001
Supervisor
Committee
Pereira, Antonio Roberto (President)
Folegatti, Marcos Vinicius
Sentelhas, Paulo Cesar
Title in Portuguese
Evapotranspiração de referência medida por lisímero de pesagem e estimada por Penman-Monteith (FAO-56), nas escalas mensal e decendial.
Keywords in Portuguese
evapotranspiração
lisímetro
meteorologia agrícola
modelo Penman-Monteith
Abstract in Portuguese
Title in English
Reference evapotranspiration measured with a weighing lysimeter and estimated by Penman-Monteith (fao-56) on a month and ten-days time scales.
Keywords in English
agricultural meteorology
evapotranspiration
lysimeter
Penman-Monteith model
Abstract in English
Reference evapotranspiration (ETo, mm d-1) was measured by a weighing lysimeter coupled with three load cells, during 1996, in Piracicaba, SP, Brazil. Operational difficulties with this kind of lysimeter during days with high intensity rainfall and also during a sequence of days with intermittent rains are discussed. The time series of measured ETo was pooled in sequences of either 10 or 30 days generating groups of mean values for such time scales. Moving averages with different steps were used to increase the number of points in each group and to test their effect upon the statistical relationships. Estimatives of mean ETo corresponding to the time intervals of the measured averages were computed with the Penman-Monteith equation following the parameterizations and procedures described in the FAO Irrigation and Drainage Paper 56, using data given by an automatic meteorological weather station located next to the lysimeter. Simple linear regression analysis (Lysimeter = b Estimative) indicates the following statistical tendencies: 1) for the 30-days time scale, Y = 1.0905 X ± 0.212 mm d-1, r2 = 0.9512 from january to june; and Y = 0.9622 X ± 0.166 mm d-1, r2 = 0.8249 from august to november; 2) for the 10-days time scale, Y = 1.0866 X ± 0.332 mm d-1, r2= 0.9158 from january to june; e Y = 0.9573 X ± 0.323 mm d-1, r2 = 0.7729 from august to november. The different time steps did not affect substantially the b value; but, in general, as the time step increased so did the mean error of the estimative due to the decrease in the number of points compared. Due to the operational difficulties in measuring ETo during periods of high intensity rains perhaps the relationships found for the second period represents better the degree of fit of the estimatives. The performance of the ETo estimatives did not change substantially when the measured net radiation was substituted by an estimative using the FAO-56 guidelines, simulating a very common situation of lack of such weather element.