Ref-ET
Soil Water Management
Evapotranspiration and Irrigation Water Requirments
Mid Snake Water Quality

 

 

 

 

ASCE-EWRI Standardization of Reference Evapotranspiration

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 2001.

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:

  • A. Description of Task Committee's methodology and procedures used to derive the standardized reference evapotranspiration equation
  • B. Summary of reference evapotranspiration equations used in evaluation
  • C. Example calculations for daily and hourly standardized reference evapotranspiration
  • D. Weather data integrity assessment and station siting
  • E. Estimating missing climatic data
  • F. Summary of reference evapotranspiration comparisons

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 download).

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, Arizona, 2000.

Paper on ASCE’s 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 Evapotranspiration Equation

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