Error assessment of climate variables for FAO-56 reference evapotranspiration

Abstract

Meteorological stations, which measure all the required meteorological parameters to estimate reference evapotranspiration (ET_o) 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 ET_o 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 ET_o 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 ET_o (i.e., MBE of −0.50 mm day⁻¹ and RMSE of 0.60–0.73 mm day⁻¹). Estimated ET_o 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 ET_o estimation at a daily time scale especially in data-limited regions in Korea.