Measured actual evapotranspiration

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AnneI
Posts: 3
Joined: Tue Sep 03, 2019 3:14 pm
Location: Germany

Measured actual evapotranspiration

Post by AnneI » Tue Sep 03, 2019 4:21 pm

Hi Everyone,

is there the possibility to use actual evapotranspiration (measured in our case) as a boundary condition? Maybe by not simulating root water uptake and modifying some input file ?

Thank you for your help,
Anne

Jirka
Posts: 4827
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Measured actual evapotranspiration

Post by Jirka » Tue Sep 03, 2019 10:44 pm

You can you actual values of evaporation and transpiration and adjust the parameters affecting the reduction from potential to actual values (e.g., Feddes parameters) such so that there is no much further reduction. However, there will likely still be some reduction. J.

AnneI
Posts: 3
Joined: Tue Sep 03, 2019 3:14 pm
Location: Germany

Re: Measured actual evapotranspiration

Post by AnneI » Tue Sep 24, 2019 9:45 am

Hi Jirka,
thank you very much for your answer.
We still have some further questions to clarify:

we have read, that Hydrus calculated the ETa from ETp. In our case we have measured ETa (actual ET) and we would like to use it. Does Hydrus do any transformation to it if we don't consider root water uptake (by not checking the option in the Hydrus main processes dialog) ?

In other words:
For modelling water flow (not considering root water uptake), if we use ACTUAL measured ET as input (not POTENTIAL), does it have an influence on the outfput (ET, Q) ?

How can we use ETa as input BC in Hydrus 1D?

Thank you for your help,
Anne

Jirka
Posts: 4827
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Measured actual evapotranspiration

Post by Jirka » Tue Sep 24, 2019 10:09 am

HYDRUS uses potential E as input and reduces it to actual E. If you enter actual E, there should be only a limited further reduction of this flux. However, you cannot prevent the code from reducing it further if water cannot deliver water towards the surface (if soil becomes dry), since an alternative is a model crash. J.

AnneI
Posts: 3
Joined: Tue Sep 03, 2019 3:14 pm
Location: Germany

Re: Measured actual evapotranspiration

Post by AnneI » Wed Sep 25, 2019 7:55 am

Thank you, Jirka.
We now have compared our results from a model run without using root water uptake and ETa as input and a model run with using root water uptake, ETa as input and zero Transpiration as BC and recieved good comparable results regarding the flux outflow. We will now use ETa as input without root water uptake.

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