Rajendtra Agricultural University

Bihār Sharīf, India

Rajendtra Agricultural University

Bihār Sharīf, India

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Prasad S.,Rajendtra Agricultural University | Kumar V.,Rajendtra Agricultural University | Sinha A.K.,Birsa Agricultural University | Singh A.K.P.,Rajendtra Agricultural University
International Agricultural Engineering Journal | Year: 2012

Accurate determination of reference evapotranspiration (ET0) is very essential to precise computation of crop water use. The FAO-56 Penman-Monteith method (FAO-56 PM) is the standard method recognized by the Food and Agriculture Organization of the United Nations for estimating reference evapotranspiration. Unfortunately, some of the weather variables, especially relative humidity, solar radiation, and wind speed are often missing, which could impede the estimation of ET0 with the FAO-56 PM method. To overcome the availability of climatic variables, assessing the accuracy and usefulness of Hargreaves method for Pusa Observatory located in the campus of Rajendra Agricultural University, Pusa is important. The Hargreaves equation showed a regular overestimation of the region, hence the method was discarded for Pusa location. Modifications were made in Hargreaves coefficient using statistical regression analysis and were calibrated from 0.0023 and 17.8 (Hargreaves equation) to 0.00162 and -3.03939 respectively. Both the Root Mean Square Error (RMSE) and the Mean Bias Error (MBE) of the comparison between ET0 computed by adjusted Hargreaves equation and that computed from FAO-56 PM method were less than 1.00 and 0.21 with a minimum of 0.77 and -0.11 mm d-1, respectively leading to small errors in the ET0 estimates. R2, χ2 -test, and index of agreement values confirmed strong relationships among data for the year from 1998 to 2006. It indicated that ET0 computed by adjusted Hargreaves equation (an average value of ETAHO 3.71 mm d-1) and that computed from FAO-56 PM method were in close agreement at Pusa region.


Prasad S.,Rajendtra Agricultural University | Kumar V.,Rajendtra Agricultural University
Journal of Agrometeorology | Year: 2013

The FAO-56 Penman-Monteith method (FAO-56 PM) is standard method recognized by the Food and Agriculture Organization of the United Nations for estimating reference evapotranspiration (ET0). Unfortunately, some of climatic variables, especially relative humidity, solar radiation and wind speed are often missing which could impede the estimation of ET0 with the FAO-56 PM method. To overcome the problem of availability of climatic variables, procedures to estimate ET0 with missing climate data are proposed as part of the FAO methodology. Therefore, assessing the accuracy of these procedures for Pusa Observatory is important. The comparison of ET0 estimates using limited data to those computed with full data set revealed that the difference between ET0 obtained from full and limited data set is small. Both the Mean Bias Error (MBE) and the Root Mean Square Error (RMSE) of the comparison were less than 0.35 and 1.00 with a minimum of "0.11 and 0.29 mm day-1, respectively, leading to small errors in the ET 0 estimates. R2, +2-test and index of agreement values confirmed strong relationships among data for the year 1998 to 2006.

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