An Australian comparison of Penman's potential evapotranspiration estimates and class A evaporation pan data

Abstract

Estimates of potential evapotranspiration are required to serve as an aid for estimating actual evapotranspiration. Penman's combination equation is generally accepted as an appropriate method for estimating potential evapotranspiration. However, as all the climatic data required to calculate Penman's potential evapotranspiration are seldom available, potential evapotranspiration is more commonly approximated as a factor times standard evaporation pan reading. In this paper, linear regression equations relating Penman's potential evapotranspiration for land surfaces to Class A evaporation pan data over several time periods are developed for various climatic regions throughout Australia. The analyses indicate that the correlations between daily estimates of Penman's potential evapotranspiration and pan data are poor, and therefore, pan data should be treated with caution if used to approximate daily potential evapotranspiration. The correlations improve over longer time periods, and the equations developed for three-day and weekly totals may be used as a last resort to approximate potential evapotranspiration in areas where climatic data required to calculate potential evapotranspiration are not available.