Analyses of equations for free water evaporation estimates


  • Karen Warnaka,

  • Larry Pochop


A comparison of six equations which estimate free water evaporation using climatological data show that the equations vary greatly in their ability to define the magnitude and variability of evaporation. The equations compared included the Kohler-Nordenson-Fox, Kohler-Parmele, Linacre, Priestley-Taylor, Stewart-Rouse, and deBruin, which range from equations requiring only temperature data to those requiring temperature, radiation, wind, and humidity. Several years of monthly estimates for May through September were made at two locations in Wyoming using each of the six equations. Means and standard deviations of the monthly data were calculated and t-tests and regressions comparing the data from the various equations and against pan data were performed.