Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Civil and Environmental Engineering

Department name when degree awarded

Agricultural and Irrigation Engineering

Committee Chair(s)

Robert W. Hill


Robert W. Hill


Lyman S. Willardson


Gary P. Merkley


Two reference crop evapotranspiration (ETr) equations were calibrated to the reference crop of alfalfa using 45 meteorological datafiles from 13 scattered sites in Utah and four sites in the neigboring states of Idaho and Wyoming.

The calibrations were done against the Kimberly version of the Penman ETr formula. The first equation required measured inputs of mean air temperature and solar radiation. It was referred to as the Temperature- Radiation ETr equation (ETr= CT x T x Rs). The second equation required measured inputs of mean minimum and mean maximum air temperatures. It was referred to as the New Hargreaves equation (ETr= K x T x TD0.5 x Ra). CT and K coefficients were found by minimizing a certain objective function which took into account 5-day sums and seasonal sums of ETr. General formulas were derived for estimating CT and K coefficients for any site in the intermountain west area for which the longitude, latitude, elevation, mean longterm July minimum temperature and mean longterm July maximum temperature were known. The average CT and K found for the study sites in Utah were 0.00999 and 0.001074 respectively.