### Definitions of Evapotranspiration quantities in Hydrus

Posted:

**Wed May 29, 2019 6:45 am**Hi,

I am new in Hydrus, thus I would like to ask 4 questions related to the Evapotranspiration quantities.

1) My understanding is that the reference crop evapotranspiration ETo can be calculated by the Penman-Monteith combination equation based on meteorological data. One way to convert ETo to potential evapotransiration rate ETp is to multiply it by crop coefficient Kc. Since Kc is not used in Hydrus-1D, is it accurate to say that Hydrus-1D sets ETo equivalent to ETp (thus assuming Kc=1)?

2) Is it accurate to state that the actual evaporation rate is calculated in Hydrus-1D as the product between the water stress function alpha and ETp, where alpha is the function used to obtain the actual water root uptake (Feddes model)?

3) If 1) is correct, what would be the right way to calculate ETp without assuming that it is equal to ETo?

4) In Hydrus Manual 4.08, in the section that discusses the hysteresis in soil hydraulic properties, it states that "where the subscripts d and w indicate wetting and drying, respectively." Shouldn't be the inverse way: w-wetting and d-drying?

Regards,

Kostas

I am new in Hydrus, thus I would like to ask 4 questions related to the Evapotranspiration quantities.

1) My understanding is that the reference crop evapotranspiration ETo can be calculated by the Penman-Monteith combination equation based on meteorological data. One way to convert ETo to potential evapotransiration rate ETp is to multiply it by crop coefficient Kc. Since Kc is not used in Hydrus-1D, is it accurate to say that Hydrus-1D sets ETo equivalent to ETp (thus assuming Kc=1)?

2) Is it accurate to state that the actual evaporation rate is calculated in Hydrus-1D as the product between the water stress function alpha and ETp, where alpha is the function used to obtain the actual water root uptake (Feddes model)?

3) If 1) is correct, what would be the right way to calculate ETp without assuming that it is equal to ETo?

4) In Hydrus Manual 4.08, in the section that discusses the hysteresis in soil hydraulic properties, it states that "where the subscripts d and w indicate wetting and drying, respectively." Shouldn't be the inverse way: w-wetting and d-drying?

Regards,

Kostas