Abstract: The aim of this research is to evaluate and analyze the forecasting of short-term daily reference crop evapotranspiration by Hargreaves-Samani equation based on temperature forecast. The observed daily meteorological data from 2002 to 2013 at Nanjing Station and the daily weather forecast data for 7-day forecast period from 2012 to 2013 are collected, and the daily ET₀ was calculated by using the FAO-56 Penman-Monteith (PM) equation according to daily meteorological data from 2002 to 2012. Furthermore, parameters in the HS equation are calibrated with 2002-2012 PM ET₀ values and the calibrated HS equation is adopted for forecasting the 7-day ET₀ with weather forecast data from 2012 to 2013. The precision and sensitivity of the forecast results are evaluated and analyzed. Results showed that the forecast result of ET₀ based on minimum temperature is more accurate than that on maximum temperature; the statistical indicators of calibrated HS equation are good, indicating the accuracy has improved; and the ET₀ estimated from calibrated HS equation are in accordance with the ET₀ estimated from PM equation, the accuracy of the HS equation has been significantly improved. Moreover, the accuracy of ET₀ declines with the increase of forecast period; the error in ET₀ is usually more sensitive to maximum temperature than that to minimum temperature, and the error in ET₀ is most sensitive to temperature forecasts in summer, while least sensitive to temperature forecasts in winter.

Key words: reference crop evapotranspiration, temperature forecast, Hargreaves-Samani equation, sensitivity analysis, precision evaluation