Publications

When weather data sets available for computing the reference evapotranspiration are incomplete or of questionable quality, there is the need to replace the FAO Penman-Monteith (PM-ET₀) method by approaches requiring reduced sets only, particularly maximum and minimum temperature. The Hargreaves-Samani (HS) equation and the PM-ET₀ using only temperature data (PMT) are considered in this study and their results are compared with those of the PM-ET₀ using full datasets. Daily data sets refer to the period 1981–2012 and to a network of 50 meteorological stations covering the wide range of climates of Inner Mongolia. For both the PMT and HS methods, the solar radiation coefficients k_Rs were calibrated and have shown to be similar for both methods and to vary with climate aridity. For the PMT, the estimation of the dew point temperature (T_dew) was performed using the minimum temperature corrected for site aridity or, for humid climates, from a value near the average temperature. This improved estimation of T_dew was essential for a good performance of the PMT method in arid conditions and when temperatures are extremely low. RMSE <1 mm day⁻¹ was obtained for both HS and PMT methods, and the modeling efficiency generally exceeded 0.85. The worse results correspond to windy and arid locations. The principal components analysis (PCA) in R-Mode have shown that the spatial variability of ET₀ computed with PM-ET₀ or with the HS and PMT methods were coherent. PCA supported the interpretation of ET₀ results. Overall, PMT performed better than HS for most locations.