Evaluation of uncertainty in evapotranspiration values by FAO56-Penman-Monteith and Hargreaves-Samani methods

摘要

Methods of calculating evapotranspiration are subject to uncertainty. It is important to evaluate their uncertainty. Using 54 years of data, this study evaluated the uncertainty values of monthly reference crop evapotranspiration calculated with the FAO-56 Penman-Monteith and Hargreaves-Samani methods. The objective of this study was to determine the range of variation in the results of each method. It was found that for both methods, the bandwidth uncertainty obtained with 95% confidence interval was more in warm months than in cold months, and the mean and variance by the Hargreaves-Samani method were always less than by the FAO-56 Penman-Monteith method. The uncertainty value of the FAO-56 Penman-Monteith method was more than of the Hargreaves-Samani method, because the number of parameters used in the FAO-56 method was more than in Hargreaves-Samani method which increased uncertainty resources.