Daily reference evapotranspiration estimation from weather forecast messages

Real-time irrigation forecast relies on the prediction of daily reference evapotranspiration. The Penman-Monteith equation has been a global standard for reference evapotranspiration(ET₀) estimation. In this study, an attempt was made to use the public weather forecast messages to predict daily ET₀ with Penman-Monteith method. The so-determined results were compared with those estimated by Penman-Monteith method, with the recorded daily weather information of an automated meteorological station in Daxing District, Beijing. The key factors of meteorological data and the difference of the calculated actual vapor pressures were compared between those from the weather forecast messages and those from the automated station records. Both sunshine hour and wind speed had significant agreement with the statistic analyses. On a daily basis, the regression coefficients (Rc) are 0.9876 and 0.8982, and the values of t-test (Tv) are 376.9042 and 122.4295, respectively. The two groups of estimated actual vapor pressures have good linear relationship (Rc and Tv being 0.9314 and 153.3015, respectively). All of their Tv values were bigger than the critical value of t-distribution (which is 2.576 as α=0.01). This indicates the high accuracy of the daily ET₀ predicted with weather forecast messages. The proposed method is quite reliable. High precision of estimated ET₀ depends on accurate weather forecast messages availability.