| Summary: | Precise estimation of reference evapotranspiration (ET<sub>0</sub>) is of significant importance in hydrologic processes. In this study, a genetic algorithm (GA) optimized back propagation (BP) neural network model was developed to estimate ET<sub>0</sub> using different combinations of meteorological data across various climatic zones and seasons in China. Fourteen climatic locations were selected to represent five major climates. Meteorological datasets in 2018–2020, including maximum, minimum and mean air temperature (T<sub>max</sub>, T<sub>min</sub>, T<sub>mean</sub>, °C) and diurnal temperature range (∆T, °C), solar radiation (R<sub>a</sub>, MJ m<sup>−2</sup> d<sup>−1</sup>), sunshine duration (S, h), relative humidity (RH, %) and wind speed (U<sub>2</sub>, m s<sup>−1</sup>), were first subjected to correlation analysis to determine which variables were suitable as input parameters. Datasets in 2018 and 2019 were utilized for training the models, while datasets in 2020 were for testing. Coefficients of determination (r<sup>2</sup>) of 0.50 and 0.70 were adopted as threshold values for selection of correlated variables to run the models. Results showed that U<sub>2</sub> had the least r<sup>2</sup> with ET<sub>0</sub>, followed by ∆T. T<sub>max</sub> had the greatest r<sup>2</sup> with ET<sub>0</sub>, followed by T<sub>mean</sub>, R<sub>a</sub> and T<sub>min</sub>. GA significantly improved the performance of BP models across different climatic zones, with the accuracy of GABP models significantly higher than that of BP models. GABP<sub>0.5</sub> model (input variables based on r<sup>2</sup> > 0.50) had the best ET<sub>0</sub> estimation performance for different seasons and significantly reduced estimation errors, especially for autumn and winter seasons whose errors were larger with other BP and GABP models. GABP<sub>0.5</sub> model using radiation/temperature data is highly recommended as a promising tool for modelling and predicting ET<sub>0</sub> in various climatic locations.
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