The PDF documents linked to this page comprise the 2001 draft report by the Environmental and Water
Resources Institute (EWRI) of the American Society of Civil Engineers (ASCE) on establishment and
definition of a benchmark reference evapotranspiration equation that standardizes the calculation of
reference evapotranspiration. The intent is to produce consistent calculations for reference
evapotranspiration and to to improve transferability of crop coefficients. The ASCE-EWRI Task Committee on
Standardization of Reference Evapotranspiration was formed in 1999 and issued the draft report in December
The final Task committee report on the ASCE Standardized Reference
Evapotranspiration Equation was published in 2005 by American Society of Civil Engineers (ASCE) and is
available for purchase from the following address:
ASCE Bookstore, ISBN
078440805, Stock Number 40805, pp 216
Most users will wish to purchase the final report from via the above link rather than download the
draft main report that describes the standardized reference evapotranspiration equation and all
computation equations. The draft appendices include additional information on committee history and
deliberations, reference equation analyses, example calculations, weather data integrity, and missing
data. The titles of appendices are as follow:
The documents are in Adobe Portable Document Format (PDF). The latest Adobe Acrobat Reader may be
obtained from Adobe at www.adobe.com.
Draft Main Report Body without Appendices (1,227 KB) Updated September 2005
Draft Report Appendices (7,390 KB) Updated September 2002 (this will take between 10 and 15 minutes to
Worksheets associated with Appendix F: ETo
Ratio Tables and ETr Ratio Tables.
Summary of the ASCE Standardized ET Method presented by R.G. Allen at
the USCID Second International Conference on Irrigation and Drainage, May 14, 2003, Phoenix, Arizona.
Paper on Issues, Requirements and Challenges in Selecting and
Specifying a Standardized ET Equation presented at the National Irrigation Symposium in Phoenix,
Paper on ASCEs Standardized Reference Evapotranspiration Equation presented at the National Irrigation Symposium in Phoenix, Arizona, 2000.
Paper on Conversion of Wright (1981) and Wright (1982)
alfalfa-based crop coefficients for use with the ASCE Standardized Penman-Monteith Reference
Paper on Comparison of Cumulative Evapotranspiration at
Kimberly, Idaho using Mean Crop Coefficients from Table 6.9 of ASCE Manual 70 for Years of Measurement by
Crop and the 1982 Kimberly Penman and ASCE Standardized Penman-Monteith Reference Methods
Memo on Quality Assessment and Control of Automated Weather Data to Managers of Agricultural Weather Networks and Associated Weather Data Systems from the Technical Committee on Evapotranspiration in Irrigation and Hydrology of the Environmental and Water Resources Institute (EWRI) of the American Society of Civil Engineers (ASCE) April 1, 2009