Operational estimates of reference evapotranspiration

(...) The Penman-Monteith and other forms of the Penman equation were compared at 11 international lysimeter sites, with the Penman-Monteith method and a Penman equation with variable wind function developed at Kimberly, ID providing the best estimates of reference ET across the sites. Ratios of computed alfalfa to grass reference ET during peak months at various locations averaged 1.32, and ranged from 1.12 to 1.43. Values of computed ratios were related to local wind and humidity conditions (...)