## DESCRIPTION

i.evapo.PT Calculates the diurnal evapotranspiration after Prestley and Taylor (1972). The Priestley-Taylor model (Priestley and Taylor, 1972) is a modification of Penman’s more theoretical equation.

## NOTES

RNETD optional output from i.evapo.potrad is giving good results as input for net radiation in this module.

Alpha values:

- 1.32 for estimates from vegetated areas as a result of the increase in surface roughness (Morton, 1983; Brutsaert and Stricker, 1979)
- 1.26 is applicable in humid climates (De Bruin and Keijman, 1979; Stewart and Rouse, 1976; Shuttleworth and Calder, 1979), and temperate hardwood swamps (Munro, 1979)
- 1.74 has been recommended for estimating potential evapotranspiration in more arid regions (ASCE, 1990). This Worked well in Greece with University of Thessaloniki.

Alpha values extracted from: http://www.civil.uwaterloo.ca/Watflood/Manual/02_03_1.htm

## SEE ALSO

i.evapo.pm, i.evapo.potrad, i.eb.netrad, i.eb.g0

## AUTHORS

Yann Chemin, GRASS Development team, 2007-08

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