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.