In this study, the spatial and temporal trends of reference evapotranspiration (ETo) and its components consisting of the energy term (ENo) and the aerodynamic term (AEo) were considered over the Korean Peninsula. The T-test and Mann–Kendall (MK) test were used to detect parameter trends after removing the effect of serial correlation from annual and seasonal time series between 1980 and 2017. Due to the lack of solar-radiation data for North Korea (NK), a regionally calibrated model based on

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... uth Korea (SK) weather data was developed to estimate daily solar radiation in NK. The results showed that spatial distribution of the ETo increased southward in the range from 705 mm/year in the northeast to 1195 mm/year in the southeast of the Korean Peninsula. The spatial patterns of the ENo and AEo varied from the minimum in the north and increased southward, reaching their maximum values in the southern parts of the Korean Peninsula. The mean annual ETo values of SK and NK were also compared. Over the 37-year period, mean annual evapotranspiration in SK was approximately 18% higher than that in NK. Moreover, mean areal ENo and AEo in SK were higher than in NK. The trend of the ENo on annual and seasonal scales was also upward. In contrast, the trend of the AEo decreased over the Korean Peninsula through all seasons and annual scales. These opposite trends in the ENo and AEo parameters mitigated the significant trends of the ETo. Finally, the stronger significant upward trend of the energy term led to significant increasing trends of ETo on the Korean Peninsula, with ENo being the dominant component in the increase of the ETo.