predicting daily reference evapotranspiration in a humid region of china by the locally calibrated hargreaves-samani equation using weather forecast data

the hargreaves-samani (hs) equation, which estimates reference evapotranspiration (et0) using only temperature as input, should be most suitable for et0 prediction based on weather forecasting data. in the current study, the hs equation is calibrated with daily et0 by the penman-monteith equation, and is evaluated to check the possibility of predicting daily et0 based on weather forecast data. the hs equation is likely to overestimate daily et0 in the humid regions of china. coefficients a and c are calculated as 0.00138 and 0.5736 according to local calibration. the calibrated hs equation performs considerably better than the original one. the proposed equation could be an alternative and effective solution for predicting daily et0 using public weather forecast data as inputs. the error of daily et0 prediction increases with the increase in the error of daily temperature range (tr) or daily mean temperature (tmean). this error is likely to be more sensitive to the error in tr than in the tmean. ensuring that tr errors are less than 2°c is necessary for perfect estimations of et0 based on public weather forecast data using the calibrated hs equation.