Forecast of reference crop evapotranspiration in Qingling River irrigation district based on improved Blaney-Criddle method

In order to improve the forecasting accuracy of reference crop evapotranspiration (ET0) in typical irrigation districts of central Yunnan and enhance the disaster prevention and mitigation resilience of irrigation areas, taking the Qingling River irrigation district as an example and using the FAO-56 Penman-Monteith (PM) method as the standard, daily observed meteorological data from 2001 to 2021 at four meteorological stations surrounding the district were utilized to evaluate the applicability of the Blaney-Criddle (BC) method and calibrate its parameters, thereby constructing an optimized BC method (OBC) for practical ET0 forecasting in the irrigation district. The results showed that the ET0 values calculated by the OBC formula were generally consistent with those calculated by the PM formula. The accuracy of the optimized BC formula increased from 78.90% to 97.48%, the root mean square error (RMSE) decreased from 1.14 mm/d to 0.68 mm/d, and the mean absolute error (MAE) reduced from 0.95 mm/d to 0.54 mm/d. The ET0 forecasting accuracy decreases as the lead time increases, but the statistical indicators for 5-day, 10-day, and 30-day lead times remained favorable, with RMSE values of 0.73, 0.74, and 0.78 mm/d, respectively, and MAE values of 0.56, 0.58, and 0.61 mm/d, respectively. The overall prediction accuracy was high, with an average accuracy of 67.24% for 30-day numerical weather forecasts, meeting the requirements for irrigation forecasting in the district. The research results can provide a scientific basis for formulating irrigation policies in the irrigation district.