Evaluation of Methodologies to Estimate Reference Evapotranspiration in Florida

The Penman-Monteith equation was considered by the United Nations Food and Agriculture Organization (FAO) as the standard method to calculate reference evapotranspiration (ETo). The lack of data availability, especially in long-term historical records, was the basic obstacle for a broader use of the FAO Penman-Monteith equation. Long-term records often included daily maximum and minimum temperatures and precipitation. In these circumstances empirical methods could be used but required calibration for local conditions and were not readily transferable to other regions. The main objectives of this study were to compare reference evapotranspiration estimated by the FAO Penman-Monteith equation to reference evapotranspiration estimated by the Priestley and Taylor and the Hargreaves empirical methods. The use of the FAO Penman-Monteith equation with estimated solar radiation, relative humidity, and wind speed was also evaluated. Daily, 10-d, and monthly values of reference evapotranspiration calculated by Penman-Monteith and the other methods were compared. The Priestley and Taylor method was found to be the best method to use when available long-term historical records included only daily temperature and precipitation. This methodology can be used in climatological studies for irrigation planning and to better understand the effects of seasonal climate variability on crop water requirements in Florida.