Short-term daily forecasting of crop evapotranspiration of rice using public weather forecasts

Abstract

Accurate forecasts of daily crop evapotranspiration (ETc) are essential for real-time irrigation management and water resource allocation. This paper presents a method for the short-term forecasting of ETc using a single-crop coefficient approach and public weather forecasts. Temperature forecasts with a 7-day lead time in 2013–2015 were retrieved and entered into a calibrated Hargreaves–Samani model to compute daily reference evapotranspiration (ET0) forecasts, while crop coefficient (Kc) empirical values were estimated from both observed ETc value and calculated ET0 values using the Penman–Monteith equation for the period of 2010–2012. Daily ETc forecasts of irrigated double-cropping rice were determined for three growing seasons during the period of 2013–2015 and were compared with ETc values measured by the weighing lysimeters at the Jiangxi experimental irrigation station in southeastern China. During the early rice season, the average mean absolute error (MAE) and root-mean-square-error (RMSE) values of ETc forecasts ranged from 0.95 to 1.06 mm day−1 and from 1.18 to 1.31 mm day−1, respectively, and the average correlation coefficient (R) ranged from 0.39 to 0.54; for late rice, the average MAE and RMSE values ranged from 1.01 to 1.09 mm day−1 and from 1.32 to 1.40 mm day−1, respectively, and the average R value ranged from 0.54 to 0.58. There could be three factors responsible for errors in ETc forecasts, including temperature forecast errors, Kc value errors and neglected meteorological variables in the HS model, including wind speed and relative humidity. In addition, ETc was more sensitive to changes in temperature than Kc. The overall results indicated that it is appropriate to forecast ETc with the proposed model for real-time irrigation management and water resource allocation.