Daily evaporative flux and meteorological data from three sites were
collected and analyzed. Analysis included evaluation of several
reference evapotranspiration estimating methods which were theoretically
based on distinct physical laws. The estimating methods included pan
evaporation, energy-based Priestly-Taylor, and combination methods with
and without biological adjustments. The data set represented three
sites with different climates. Analysis included comparisons of
evapotranspiration estimating methods, statistical analysis, linear
regression analysis, and a detailed study for possible seasonal trends.
An attempt to quantify the effect of climate on the original Penman
method and the original Priestly-Taylor method using three variables
was performed. The variables included average air relative humidity,
incoming shortwave radiation, and wind speed at 2 m height. Validation
of the derived climatic coefficients for the three sites was performed
using a subset of the three data sets and a fourth simulated data set.
Moving average analysis for the various evapotranspiration
estimating methods was performed at each of the three sites. The
objective was to estimate the optimum averaging interval for a particular
estimating method at each site. Five days averaging interval was found
to be adequate to reduce substantially reduce the standard error of
estimate and increase the coefficient of determination for all methods at
each site
