Software for estimating reference evapotranspiration using limited weather data

The FAO-56 Penman-Monteith combination equation (FAO-56 PM) has been recommended as the standard equation for estimating reference evapotranspiration (ET₀). The FAO-56 PM equation requires the numerous weather data that are not available in the most of the stations. The main goal of this paper is to present the software for estimating reference evapotranspiration, focusing on the feature of using limited weather data. This is simple Windows-based and user-friendly software provides methods to estimate extra-terrestrial radiation, maximum sunshine hours, daily net radiation and daily/monthly ET₀. The program is written in C# and includes comprehensive technical documentation. The software is available for free download.The weather data for this study were obtained from CIMIS for Davis weather station. The reduced-set FAO-56 PM approaches and adjusted Hargreaves equation were compared to the full-set FAO-56 PM equation. The FAO-56 reduced-set PM ET₀ estimates were in closest agreement with FAO-56 full-set PM ET₀ estimates. The adjusted Hargreaves equation (AHARG) was found to be in very good agreement with the full-set FAO-56 PM. This program is the first software facilitating calculation of ET₀ only with air temperature parameter.