Comparative evaluation of calibrated temperature-, and radiation-based ET0 equations developed for semi-arid climatic conditions based on standardized FAO56-PM model
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Date
2018-08
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
The present study was undertaken to calibrate, validate and evaluate different temperature-, and radiation-based ET0 equations on daily, weekly, monthly, and seasonal (crop and weather) basis for semi-arid climatic conditions of Parbhani and Udaipur in comparison to standard FAO56-PM model with two specific objectives as, (i) to calibrate, validate and evaluate performance of various temperature-, and radiation-based ET0 equations in comparison to FAO56-PM model, and (ii) to calibrate and evaluate performance of all considered ET0 equations by using MicrosoftTM Excel Solver in comparison to FAO56-PM model. In this study, individual year was converted into 52 Standard Meteorological Weeks (SMWs), 12 months, three crop seasons (rabi, zaid and kharif) and three weather seasons (winter, summer and monsoon) in tune with CWS-1 format suggested by Indian Meteorological Department, Pune. The MicrosoftTM Excel was used as computing tool for conducting analysis and draw fruitful inferences from them. Prior to analysis, quality control of daily weather was also ensured by detecting missing data and outliers. The results showed that at all timescales, almost all calibrated ET0 equations performed well and extended better results in comparison to their original versions. Further, it was found that, calibrated Hargreaves-Samani M3 equation was found best at both places on daily, weekly, monthly, and weather season basis, while Hargreaves-Samani M1 performed best at both places on crop season basis. Among temperature-based ET0 equations, Romanenko equation was found worst at all timescales for both the places. Among radiation-based ET0 equations, Valiantzas (2) equation performed best while Irmak-Rn ET0 equation performed worst at all timescales for both places. Determination of calibration coefficient of different temperature- and radiation-based ET0 equations by using MicrosoftTM Excel Solver was found at-par in comparison of tedious and time-consuming MicrosoftTM Excel utility.
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