The Penman-Monteith (PM) method for estimation of reference evapotranspiration (ET0) uses numerous input data that are often missing in many regions. In such circumstances, temperature-based equations can be used for estimating ET0. The primary objective of this note was to compare the calibrated temperature-based ET0 approaches with the PM equation using meteorological data from fifteen CLIMWAT stations located in the Pannonian Basin. The most of these locations are classified as humid. Twelve temperature-based PM, Hargreaves and Thornthwaite equations were evaluated according to the standard PM method. The regionally calibrated Hargreaves equation (HT) gave the lowest RMSE at seven sites and the second lowest RMSE at three sites. New regionally calibrated Thornthwaite approach (TT) yielded the lowest RMSE three times and the second lowest RMSE seven times. These approaches resulted in the lowest average RMSE for all fifteen locations (0.28 and 0.30 mm day−1, respectively). The other temperature-based approaches significantly fall behind the HT and TT equations at most stations. The overall results show the advantage of the HT approach except for a few southeast stations where the TT approach is dominant. It can be concluded that the regionally calibrated temperature-based approaches (HT and TT) are the most suitable to estimate ET0 in the Pannonian Basin.

Supplement to: Trajkovic, Slavisa; Gocic, Milan; Pongracz, Rita; Bartholy, Judit; Milanovic, Mladen (2020): Assessment of Reference Evapotranspiration by Regionally Calibrated Temperature-Based Equations. KSCE Journal of Civil Engineering, 24(3), 1020-1027