Error assessment of climate variables for FAO-56 reference evapotranspiration

Meteorological stations, which measure all the required meteorological parameters to estimate reference evapotranspiration (ETo) using the Food and Agriculture Organization Penman–Monteith (FAO56-PM) method, are limited in Korea. In this study, alternative methods were applied to estimate these parameters, and the applicability of these methods for ETo estimation was evaluated by comparison with a complete meteorological dataset collected in 2008 in Korea. Despite differences between the estimation and observation of radiation and wind speed, the comparison of ETo showed small differences [i.e., mean bias error (MBE) varying −0.22 to 0.25 mm day−1 and root-mean-square-error (RMSE) varying 0.06–0.50 mm day−1]. The estimated vapor pressure differed considerably from the observed, resulting in a larger discrepancy in ETo (i.e., MBE of −0.50 mm day−1 and RMSE of 0.60–0.73 mm day−1). Estimated ETo showed different sensitivity to variations of the meteorological parameters—in order of vapor pressure > wind speed > radiation. It is clear that the FAO56-PM method is applicable for reasonable ETo estimation at a daily time scale especially in data-limited regions in Korea.

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