an important component in water-balance and irrigation scheduling models.
While the FAO-56 Penman-Monteith method
has become the de facto standard for estimating reference evapotranspiration (ETo), it is a complex
method requiring several weather parameters. Required weather data are
oftentimes unavailable, and alternative
methods must be used. Three alternative ETo methods, the FAO-56
Reduced Set, Hargreaves, and Turc methods, were evaluated for use in
Mississippi, a humid region of the USA, using only measurements of air temperature.
The Turc equation, developed for use with measured temperature and solar radiation,
was tested with estimated radiation and found to provide better estimates of FAO-56 ETo than the other methods. Mean bias errors of 0.75,
0.28, and -0.19 mm, mean
absolute errors of 0.92, 0.68, and 0.62 mm,
and percent errors of 22.5%, 8.5%, and -5.7% were found for daily estimates for
the FAO-56 Reduced Set, Hargreaves,
and Turc methods, respectively.