defaultconstants {Evapotranspiration} | R Documentation |

## Universal constants Required for Calculating Evapotranspriation

### Description

This data set contains the universal constants required for calculating evapotranspiration in function `ET`

, which should be kept unchanged for most conditions. Please note that additional constants may be ET models - check the manual for individual ET models for details.

### Usage

data(defaultconstants)

### Format

A list containing 20 constant values including:

*lambda* latent heat of evaporisationin = 2.45 MJ.kg^-1 at 20 degree Celcius,

*sigma* Stefan-Boltzmann constant = 4.903*10^-9 MJ.K^-4.m^-2.day^-1,

*Gsc* solar constant = 0.0820 MJ.m^-2.min^-1

*Roua* mean density of air = 1.2 kg.m^-3 at 20 degree Celcius

*Ca* specific heat of air = 0.001013 MJ.kg^-1.K^-1

*G* soil heat flux negligible for daily time-step = 0 (Allen et al., 1998, page 68)

*alphaA* Albedo for Class-A pan = 0.14

*alphaPT* Priestley-Taylor coefficient:

= 1.26 for Priestley-Taylor formula (Priestley and Taylor, 1972, Sect. 6;
Eichinger et al., 1996, p.163);

= 1.31 for Szilagyi-Jozsa formula (Szilagyi and Jozsa, 2008);

= 1.28 for Brutsaert-Strickler formula (Brutsaert and Strickler, 1979),

*ap* constant in Penpan formula = 2.4,

*b0* constant in Morton's procedure = 1 (Chiew and McMahon, 1991, Table A1),

*b1* constant in Morton's procedure = 14 W.m^-2 (Chiew and McMahon, 1991, Table A1),

*b2* constant in Morton's procedure = 1.2 (Chiew and McMahon, 1991, Table A1),

*e0* constant for Blaney-Criddle formula = 0.81917 (Frevert et al., 1983, Table 1),

*e1* constant for Blaney-Criddle formula = -0.0040922 (Frevert et al., 1983, Table 1),

*e2* constant for Blaney-Criddle formula = 1.0705 (Frevert et al., 1983, Table 1),

*e3* constant for Blaney-Criddle formula = 0.065649 (Frevert et al., 1983, Table 1),

*e4* constant for Blaney-Criddle formula = -0.0059864 (Frevert et al., 1983, Table 1),

*e5* constant for Blaney-Criddle formula = -0.0005967 (Frevert et al., 1983, Table 1),

*epsilonMo* Land surface emissivity in Morton's procedure = 0.92,

*sigmaMo* Stefan-Boltzmann constant in Morton's procedure = 5.67e-08 W.m^-2.K^-4.

### Source

various references

### See Also

`constants`

[Package

*Evapotranspiration* version 1.15

Index]