Standardization of Reference Evapotranspiration
Evapotranspiration represents the loss of water from the earth’s surface through the combined processes of evaporation (from soil and plant surfaces) and plant transpiration (i.e. internal evaporation). Reference evapotranspiration is the rate at which readily available soil water is vaporized from vegetated surfaces.
The following is a link to a video presentation entitled: "History, intent and structure of reference ET standardization and its role in ET models" given by R. G. Allen at the American Society of Agronomy Annual Meeting on Nov. 10, 2020.
The Environmental and Water Resources Institute (EWRI) of the American Society of Civil Engineers (ASCE) issued the following report that defines a benchmark reference evapotranspiration equation that standardizes the calculation of reference evapotranspiration. The intent is to produce consistent calculations for reference evapotranspiration and to improve transferability of crop coefficients.
Additional resources:
- ASCE Standardized Reference Evapotranspiration Equation draft main report body without appendices (updated Sept. 2005) (PDF)
- ASCE Standardized Reference Evapotranspiration Equation report appendices link to ASCE-SREE-appendix (PDF)
- Issues, Requirements and Challenges in Selecting and Specifying a Standardized ET Equation (PDF)
- Conversion of Wright and Wright alfalfa-based crop coefficients (PDF)
- Comparison of Cumulative Evapotranspiration (PDF)
- Quality Assessment and Control of Automated Weather Data (PDF)
History, intent and structure of reference ET standardization and its role in ET models
Rick G. Allen, Ph.D. at the American Society of Agronomy Annual Meeting on Nov. 10, 2020