Forecast of Daily Reference Evapotranspiration Using a Modified Daily Thornthwaite Equation and Temperature Forecasts†

Short-term daily reference evapotranspiration (ET0) forecasts are helpful for real-time irrigation decision making. Using a modified daily Thornthwaite (TH) equation and temperature forecasts, a method was proposed for ET0 forecasting. Daily meteorological data were obtained from the selected representative stations located in different climate regions in China. Data were collected from 2000 to 2012 to calibrate and validate the modified TH equation against the FAO56 Penman-Monteith (FAO56-PM) equation. Temperatures forecasts for a 7-day forecast period in 2012-2017 were input to the calibrated TH equation to forecast ET0. The results showed that the ET0 forecasting performance with the modified TH equation and temperature forecast was further improved at all stations after month-wise calibration. The average accuracy of forecasted ET0 ranged from 87.3 to 91.2%, the average values of root mean square error (RMSE) ranged from 0.86 to 1.01 mm day ? (1); moreover, the average of regression coefficient (b), determined coefficient (R-2) and modelling efficiency (EF) are greater than 0.82, 0.87 and 0.81. Furthermore, the sensitivity analyses show that the percentage change in ET0 forecast was more sensitive to predictions of temperature during the spring-summer period than autumn-winter. The proposed method produced good results of ET0 forecasts and can be a feasible solution for short-term forecasting of ET0. (c) 2018 John Wiley & Sons, Ltd.