| Reference Evapotranspiration |
|---|
Grass and Alfalfa Reference Evapotranspiration as Computed for the Washington State University Research and Extension Unit near Mount Vernon, Washington, and Grass Consumptive Use Computed for Clearbrook, Washington, in inches
| January | February | March | April | May | June | July | August | September | October | November | December | Total | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Grass Reference ET1 | 0.74 | 1.09 | 1.98 | 2.80 | 4.23 | 4.62 | 4.99 | 4.31 | 2.73 | 1.32 | 0.74 | 0.61 | 30.16 |
| Alfalfa Reference ET1 | 0.47 | 0.81 | 1.74 | 2.66 | 4.43 | 4.95 | 5.43 | 4.65 | 2.92 | 1.27 | 0.56 | 0.35 | 30.24 |
| Grass Consumptive Use2 | 0.12 | 0.58 | 1.46 | 2.73 | 4.05 | 4.69 | 5.58 | 4.44 | 3.01 | 1.31 | 0.29 | 0.02 | 28.28 |
1. Daily grass and alfalfa reference evapotranspiration at the Washington State University (WSU) Research and Extension Unit near Mount Vernon, Washington, for October 1991 to December 1999 (Washington Public Agricultural Weather System (WPAWS), 2000) were averaged by month and among years. Grass reference evapotranspiration was computed by the FA0-24 Penman technique and alfalfa reference evapotranspiration was computed by the Kimberly Penman technique (M.J. Hattendorf, Director, WPAWS, oral commun., January, 2000).
2. Grass consumptive use is the combined rates of evaporative loss and rate of incorporation of water into plant tissues for grass 3 to 6 inches tall forming an extensive surface cover (James and others, 1988). Grass consumptive use was computed using the Blaney-Criddle technique as is described by James and others (1988), using monthly average air temperature at Clearbook, Washington, for 1961 to 1990 (Hydrosphere Data Products, Inc., 1999).
References Cited
James, L.G., Erpenbeck, J.M., Bassett, D.L., and Middleton, J.E., 1988, Irrigation requirements for Washington- estimates and methodology: Washington State University Extension Bulletin 1513, 37 p.
Hydrosphere Data Products, Inc., 1999, ClimatedataTM vol. 10.3, NCDC Summary of the Day, West 2: Boulder, Colorado, Hydrosphere Data Products, Inc., CD-ROM.
Washington Public Agricultural Weather System, 2000, Reports-- Evapotranspiration: Prosser, Washington, Washington State University Cooperative Extension, digital data, on-line on the World Wide Web from the Universal Resource Locator (URL): http://index.prosser.wsu.edu, accessed January 5, 2000, ASCII format.
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