Comparison of reference evapotranspiration estimated by Penman-Monteith and a Class A pan across the 2016 and 2017 dry seasons in Yopal, Casanare, Colombia
DOI:
https://doi.org/10.17268/Keywords:
reference evapotranspiration, Class A pan, Penman-Monteith, irrigation scheduling, OrinoquiaAbstract
Reliable estimation of reference evapotranspiration (ETo) is essential for irrigation scheduling in the Colombian Orinoquia, where incomplete agrometeorological records often limit the routine application of data-demanding methods. This study compared ETo estimated by the FAO Penman-Monteith method and by a Class A evaporation pan in Yopal, Casanare, during the 2016 and 2017 dry seasons, testing whether the pan could reproduce Penman-Monteith ETo without significant bias. A total of 52 paired observations were analyzed, with 26 records for each year. Penman-Monteith ETo was calculated from Davis WeatherLink meteorological data following FAO-56 procedures, while pan-based ETo was obtained from measured evaporation using a fixed pan coefficient (Kp) of 0.70. Across both years, mean ETo was 4.24 mm d⁻¹ for Penman-Monteith and 5.40 mm d⁻¹ for the Class A pan, with a significant pooled bias of 1.17 mm d⁻¹ (p < 0.001). Agreement was moderate overall, but strongly dependent on year. The pan performed well in 2017, yet substantially overestimated ETo in 2016. These results indicate that a fixed Kp of 0.70 is not temporally stable, and that local calibration and validation across seasons are necessary before the Class A pan can be used as a substitute for Penman-Monteith in Yopal.
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