Reference Evapotranspiration (ETo)

CIMIS uses the Modified Penman-Monteith Equation to calculate the reference evapotranspiration rate of grass.  CIMIS uses hourly inputs generated by the weather stations using the following variables: air temperature, relative humidity, wind speed, vapor pressure, elevation of station above sea level and calculated net radiation.

To learn more about meteorological factors determining ET visit

       http://www.fao.org/docrep/X0490E/x0490e00.htm - Crop evapotranspiration - Guidelines for computing     crop water requirements - FAO Irrigation and drainage paper 56

http://www.fao.org/docrep/X0490E/x0490e07.htm.

The equation for estimating ETo is complex and could be viewed in detail at the following sites:

www.cimis.water.ca.gov

http://www.gsf.de/UFIS/ufis/modell65/gle325.html http://www.fao.org/docrep/X0490E/x0490e08.htm .

To understand Evapotranspiration further visit these sites:

http://www.fao.org/docrep/X0490E/x0490e04.htm,

http://www.agu.org/revgeophys/engman00/node6.html

http://ag.arizona.edu/pubs/water/az1194.pdf

http://www.oznet.ksu.edu/library/ageng2/mf2389.pdf. 

http://biomet.ucdavis.edu/evapotranspiration/ET101/ET101.pdf - from UC Davis Biometeorology