International Journal of
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Research Article Volume 10 Issue 1
Local and regional calibration of Hargreaves-Samani equations for reference evapotranspiration estimation in a semiarid climate
Koffi Djaman, Komlan Koudahe, Ulavayya K Shanwad, Yusuf O Anifowoshe
Received: December 25, 2025 | Published: January 13, 2026
Citation: Djaman K, Koudahe K, Shanwad UK, et al. Local and regional calibration of Hargreaves-Samani equations for reference evapotranspiration estimation in a semiarid climate. Int J Hydro. 2026;10(1):1-11. DOI: 10.15406/ijh.2026.10.00420
Abstract
Reference evapotranspiration is estimated by several equations with diverse performance and accuracy. While the Penman-Monteith equation is revealed as the most accurate estimation method, it requires several weather variables that are not measured at most weather stations across the globe. This study aimed to evaluate the Hargreaves evapotranspiration equations and to adjust the parameters or constants within the different equation to improve their performance and accuracy across the State of New Mexico, USA. The results showed that the calibration of the different Hargreaves equations improved equation performance. Calibrated equations’ King-Gupta Efficiency (KGE) ranging from 0.73 to 0.97, the Nash- Sutcliffe Efficiency Coefficient (NSE) from 0.84 and 0.88, coefficient of determination (R2) from 0.76 to 0.93, and the regression slope from 0.97 to 1.04. All equations showed poor performance at the Corona Range which is a hyper arid station without any influence of agricultural irrigation management in the area. The calibrated Equation 11 showed more accuracy and should be recommended for daily reference evapotranspiration across the State of New Mexico.
Keywords: reference evapotranspiration, Hargreaves, calibration/validation, New Mexico
©2026 Djaman, et al. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and build upon your work non-commercially.