Evapotranspiration

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epelde.ane@gmail.com
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Evapotranspiration

Postby epelde.ane@gmail.com » Wed Nov 02, 2011 10:57

Hello all!

I´m doing a simulation without vegetation and homogeneous soil. The thing is that I don´t know which value I have to write in these keywords:
As I want the evapotranspiration be computed --> EVAPOTRANSPIRATION: 1
Then, the vegetation module is switched off. But, I dont know what to do with EVAPOTRANSPIRATION_METHOD and EVAP_METHOD.
I undestand which is the difference between the different possibilities, but I dont know which value I have to give for this situation.

Should I put EVAPOTRANSPIRATION_METHOD : 2 so that it calculates the evaporation from surface soil? If I do that I get an error saying that I should change Evap method into 3 (which means no evaporation).

So what can I do with this?
Thank you!

Jauch
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Posts: 98
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Re: Evapotranspiration

Postby Jauch » Wed Nov 02, 2011 12:08

Hi Ane.

Sorry for this, because it's my fault.
These keywords are confusing and should be changed in the future.

For now, let me explain how they work.

In the BASIN input file:

EVAPOTRANSPIRATION
: Can be 1 (ON) or 0 (OFF)
EVAPOTRANSPIRATION_METHOD: Can be 1 or 2. 1 Means that Mohid will use a simpler method for evapotranspiration that do not separate it into evaporation and transpiration. 2 Means that Mohid will separate the evapotranspiration into evaporation and transpiration. Method 2 requires VEGETATION keyword to be set to 1 and the related input file for the vegetation module must exist.

The EVAP_... keywords are related to evaporation.

EVAP_METHOD: Can be set to 1, 2 or 3.
1: Means that water above soil surface (water column & canopy water) that did not infiltrate will be evaporated by Basin module using Latent Heat method.
2: Means that water above soil surface (water column & canopy water) that did not infiltrate will be evaporated by Basin module using ET0 method.
3: Means that water above soil surface (water column & canopy water) that did not infiltrate will not be evaporated by Basin module

If EVAP_METHOD is set to 3, EVAP_FROM_CANOPY and EVAP_FROM_WATER_COLUMN is ignored. Otherwise:
EVAP_FROM_CANOPY: If set to 0, basin will not evaporate water stored in the canopy (related to the Vegetation property "specific leaf storage"). If set to 1, it will evaporate this water using the method chosen with the EVAP_METHOD keyword.
EVAP_FROM_WATER_COLUMN: If set to 0, basin will not evaporate water on the water column above the soil surface. If set to 1, it will evaporate this water using the method chosen with the EVAP_METHOD keyword.

Now, there are some points that are important here.

if you set EVAP_METHOD to 0 or EVAP_FROM_CANOPY to 0 and "leaf area storage" property, in the vegetation input file, is set to a value other than 0, you will have a fraction of the rain that will be "lost", because it will be stored in the leaves of the vegetation canopy and (probably) will never get out of there. Unless you are making a simulation with a dense forest where the water retained in the leaves are very important, I recomend you to set the "leaf area storage" property to a value of 0 and set EVAP_FROM_CANOPY to 0 also.

If you set the EVAP_FROM_WATER_COLUMN to 0, than you have to set the IGNORE_WATER_COLUMN_ON_EVAP keyword to 1 in the Porous Media input file. This keyword tells to the Porous Media Module that it have to evaporate water from soil even if there is water above soil surface. The normal behaviour (IGNORE_WATER_COLUMN_ON_EVAP = 0) is that if there is a water column above soil surface, than the evaporation of soil water will stop.

What I usually use for my simulations is:

Code: Select all

!Basin input file
EVAPOTRANSPIRATION        : 1
EVAPOTRANSPIRATION_METHOD : 2
EVAP_METHOD               : 3

!Vegetation input file
<beginproperty>
NAME                      : specific leaf storage
UNITS                     : m3/m2
DESCRIPTION               : plant specific leaf storage
EVOLUTION                 : 1
FILE_IN_TIME              : NONE
INITIALIZATION_METHOD     : CONSTANT
DEFAULTVALUE              : 0.0
REMAIN_CONSTANT           : 1
OUTPUT_HDF                : 0
TIME_SERIE                : 0
<endproperty>

!Porous Media input File
IGNORE_WATER_COLUMN_ON_EVAP : 1


If you don't want to use vegetation:

Code: Select all

!Basin input file
EVAPOTRANSPIRATION        : 1
EVAPOTRANSPIRATION_METHOD : 1
EVAP_METHOD               : 3

!Porous Media input File
IGNORE_WATER_COLUMN_ON_EVAP : 1


This works well for me.
In the future we will work on the keywords and on the methods. :)

epelde.ane@gmail.com
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Posts: 172
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby epelde.ane@gmail.com » Wed Nov 02, 2011 16:43

Hi eduardo!
Thanks for the reply :)

I think I didn´t understand you well, because what I undestand with your explanations, that in your both examples, with and without vegetation, you are desactivating the evaporation.
In both examples you have set EVAP_METHOD:3 which means that water will not be evaporated neither from soil or canopy, will it?
If I want to take evaporation into account, shouldn´t I set:

EVAPOTRANSPIRATION:1
EVAPOTRANSPIRATION_METHOD : 2 (If I set it to 1 without vegetation water output from the basin won´t be null? I thought that unless computing vegetation, I´ll always have to set it 2)
EVAP_METHOD : 1 or 2 (But never 3 if I want to compute the water output from water column or canopy (which in my case will be null as I dont have vegetation)
Not right?

I think I´m misunderstanding something cause this doesn´t fit with your explanations, but I can´t find what is it. :(

Jauch
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Posts: 98
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby Jauch » Wed Nov 02, 2011 22:38

Hi Ane.

No, I'm not deactivating evaporation. :)
Let's "separate" things to make this more clear.

Evapotranspiration is the combined proccess of evaporation and transpiration.

Transpiration is the water that is lost to atmosphere, whose origin is the soil, through vegetation.

Evaporation is the water that is lost to atmosphere, from 3 different "pools" (in Mohid Land):
1. Water that is stored in leaves (canopy), after a rain, for example
2. Water that is above the soil surface (water pools, formed because the amount of water that infiltrates is lesser than the water that is coming from rain/irrigation)
3. Water that is "inside" the soil (first layer only).

When you set the EVAPOTRANSPIRATION_METHOD to 1, you are telling to Mohid Land that you want to use a "simplified" method to compute the evapotranspiration. You use this method when you don't know the vegetation or it is not important to know how much of the evapotranspiration is coming from evaporation and how much is coming from transpiration. You set EVAPOTRANSPIRATION_METHOD to 2 when you want to know these two values, when you want to know how much the vegetation had transpirated and how much was evaporated from soil/surface/leaves.

So, if you set EVAPOTRANSPIRATION_METHOD to 2, you need to setup vegetation. If you set to 1, you don't need.

About the EVAP_METHOD.

The EVAP_METHOD keyword is related only to evaporation of water in the leaves and over the surface (pools of water/water column).

When we set EVAP_METHOD to 3, we're saying that water will not be evaporated from soil surface and leaves. That is correct.
If you are using the "simple" method by setting EVAPOTRANSPIRATION_METHOD to 1 (wich do not separate evaporation from transpiration and thus do not use vegetation), you do not have problems with the water stored in the canopy, because you don't have a canopy.

But you are troubled about the water on soil and above soil. Well, in fact, using the EVAPO_METHOD set to 3, the water ABOVE soil will not be evaporated. So, it's advisable to set the keyword IGNORE_WATER_COLUMN_ON_EVAP to 1. Why? Because doing this, you will continue to evaporate from soil (inside) even if there is water over soil surface (water column > 0). This will speed up the infiltration of the water that is over the surface and the effect will be almost the same as if you were evaporating the water on the surface instead of the water inside the soil. It's not the same thing but works.

But if you really want to evaporate the water over the surface, because this is important like when there is water column for several days, and yet you do not want to worry about vegetation, you can use this setup:

Code: Select all

!Basin input file
EVAPOTRANSPIRATION        : 1
EVAPOTRANSPIRATION_METHOD : 1 ! Tells to work as evaporation and transpiration is one thing, not two separeted proccess
EVAP_METHOD               : 1 !or 2 (1 = latent heat, 2 = ET0 method) This is the method for compute evaporation from over soil surface and from leaves
EVAP_FROM_CANOPY          : 0 !Tells that we will not evaporate water from leaves (because we do not have vegetation)

!Porous Media input File
IGNORE_WATER_COLUMN_ON_EVAP : 0


This setup will evaporate water from surface and if the surface has water, will stop the evaporation from soil until there is no more water on the surface (all of it was evaporated or infiltrated).
The EVAP_FROM_CANOPY set to 0 will prevent an error because you don't have vegetation.

I will ask David to complement (and correct) my explanation :)

epelde.ane@gmail.com
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Posts: 172
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Re: Evapotranspiration

Postby epelde.ane@gmail.com » Thu Nov 03, 2011 09:22

Thank you! :)

epelde.ane@gmail.com
MOHID Advanced user
Posts: 172
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby epelde.ane@gmail.com » Mon Dec 05, 2011 10:47

Hello!

I´ve tried doing different simulations with no vegetation and changes in the evapotranspirations to see how change the results. But I´m only allowed to set EVAP_METHOD: 3 when I set EVAPOTRANPIRATION_METHOD:1.
If I set that configuration I´m telling that i dont want any evaporation, arent I? and I dont want it. This is what I have:
in basin module:
EVAPOTRANSPIRATION : 1
EVAPOTRANSPIRATION_METHOD : 1
EVAP_METHOD : 3 (it doesn allow neither 1 or 2)
EVAP_FROM_CANOPY : 0
EVAP_FROM_WATER_COLUMN : 1

in porous media module:
IGNORE_WATER_COLUMN_ON_EVAP : 0

Why can be this happening?
Thanks,
ane

Jauch
Site Admin
Posts: 98
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby Jauch » Mon Dec 05, 2011 13:20

Hi Ane :-)

If you want evaporation, you have to set EVAPOTRANSPIRATION_METHOD = 2.

EVAP_METHOD is a keyword that defines if BASIN will or will not evaporate water in the water column and in the leaves storage.
EVAP_METHOD = 3 tell that the BASIN module will not evaporate, but this do not means that will not exist evaporation (unless you set EVAPOTRASNPIRATION_METHOD = 1).
In the case were you set EVAPOTRANSPIRATION_METHOD to 2 and EVAP_METHOD to 3, you can set IGNORE_WATER_COLUMN_ON_EVAP = 1, so the POROUS MEDIA module will still evaporate water inside the soil.

The fact that EVAP_METHOD only can get the value 3 when you set EVAPOTRANSPIRATION_METHOD = 1 is due the fact the when you set the last one to 1, you are telling the model that you do not want to have evaporation, but you want the water been lost to the atmosphere only by plants, via transpiration. So, BASIN can't evaporate in this method and the EVAP_METHOD only accept the value 3. This has a drawback that avoid the evaporation of water on the leaves and, because of this, I recommend to set the leaf storage property in VEGETATION module to 0.

SO,
EVAPOTRANSPIRATION_METHOD:
1 - Defines that you want ONLY transpiration
2 - Defines if you want transpiration AND evaporation

For the BASIN module (only), EVAP_METHOD:
1 - Defines that you want to evaporate water (above soil) using LATENT HEAT method
2 - Defines that you want to evaporate water (aboce soil) using FAO method
3 - Defines that module BASIN will not evaporate water. Actually, mandatory when setting EVAPOTRANSPIRATION to 1.

IGNORE_WATER_COLUMN_ON_EVAP is a boolean keyword that can accept only 1 (ON) and 0 (OFF)
If you set it to 0 (OFF), you tell the POROUS MEDIA module that if exists water ABOVE the soil surface (a column of water), the evaporation of the water inside the soil will stop. If you set to 1, the evaporation will continue. This was done to make it possible to evaporate water INSIDE the soil when you set, in the BASIN, EVAP_METHOD = 3.

But if you are using EVAPOTRANSPIRATION_METHOD = 1, than you do not want evaporation and this keyword is irrelevant in this case.

I know this is a little bit "obscure" and in the next few weeks we will, probably, change this to a more compreensive set of keywords and features. I'll discuss this with David and Frank.
For now, you can see some more info here:

http://wiki.mohid.com/wiki/index.php?title=Module_Basin
http://wiki.mohid.com/wiki/index.php?ti ... nspiration
http://wiki.mohid.com/wiki/index.php?ti ... orousMedia

epelde.ane@gmail.com
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Posts: 172
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby epelde.ane@gmail.com » Mon Dec 05, 2011 17:06

Thanks again :)
Sorry,I find this quite confussing..
As you told me that EVAPOTRANPIRATION_METHOD:2 needed the vegetation module, I "made up" that it was related to transpiration process. I´m trying to recreate different simulations´ configuration to see if I undestood correctly and I´ll post it, ok?
Regards,
Ane

Jauch
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Posts: 98
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby Jauch » Mon Dec 05, 2011 17:26

Ok, no problem.

In fact, both values (1 - transpiration only & 2 transpiration+evaporation) of EVAPOTRANSPIRATION_METHOD keyword require the vegetation modeule to be setup. You can avoid the setup of vegetation module only if you will not simulate evapotranspiration.

But if you want to evaporate from soil but do not want to simulate vegetation (or the transpiration process), you can setup the vegetation module with constants for the properties.
Use values of 0 to leaf area index, leaf storage, roots, etc, and put a value lower than 1 in the crop coefficient. I usually use something around 0.3 to simulate soil without vegetation.

This way you can use EVAPOTRANSPIRATION_METHOD set to 2, to simulate evaporation, but will not have transpiration, even if you're using the vegetation module.

epelde.ane@gmail.com
MOHID Advanced user
Posts: 172
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby epelde.ane@gmail.com » Fri Dec 09, 2011 12:42

OK!! thank you!! much more clear with the last post :D
this was the only situation I didnt know how to simulate (the one with evaporation from soil and canopy but with no tranpiration).. well, for now I´ve just been thinking about them, but i´ll try next week.

Now, I see that potential evaporation and potential transpiration can be calculated just with the keyword 2 in evapotranspiartion_method. but, how is it calculated actual evapotranspiration?? is not the same of crop evapotranspiration?
and how are calculated actual evaporation and actual transpiration?

Regards,

epelde.ane@gmail.com
MOHID Advanced user
Posts: 172
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby epelde.ane@gmail.com » Mon Dec 12, 2011 12:11

Hello again :)
Trying to set the configuration needed for evaporation, transpiration and so on, as you said in your last post, I need the vegetation module to be active (previously,I had thought that I wouldnt need it because you dont need vegetation to have evaporation proccess, so this is why I had so much confussion with all this..).
Now, I want to simulate just evaporation proccess, but I´m asked about the vegetation module. So, I have to set the simpliest configuration, that would be, with constant values set to 0.0 (as you told me) because it doesnt make any difference to me the vegetation. In fact, it would be as taking into account vegetation with no leafs, no roots..right?
So, before starting with real vegetation, is better to start with the whole catchment covered by the same vegetation? (like a grid with same value in all the cells?). And then, when I start with transpiration as well, do you recommend to start with a area of a kind of vegetation above my cell (where I put the time serie), an extense area,..?

Thanks in advance!

davidbrito
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Posts: 189
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby davidbrito » Mon Dec 19, 2011 18:39

Hello Ane,

A lot of questions to answer:
about what is crop evapotranspiration and all go to http://www.mohid.com/wiki/index.php?tit ... nspiration
and let me know if you are helped.


About the evapotranspiration, just to correct the previous post, actual code lets you to run EVAPOTRANSPIRATION_METHOD : 1 and no vegetation.
EVAPOTRANSPIRATION_METHOD : 1 means that the potential evapotranspiration will be taken from one process only between tanspiration and evaporation in soil. So, if vegetation exists water is taken by transpiration in soil, if vegetation does not exist water is taken from evaporation in soil.
EVAPOTRANSPIRATION_METHOD : 2 allows that the potential evapotranspiration may be separated in potential evaporation and potential transpiration (with LAI) and then evaporation is done in porous media surface and transpiration in vegetation roots.

So I would suggest to try to try only evaporation using in basin data file:
EVAPOTRANSPIRATION_METHOD : 1
VEGETATION : 0
all the potential evapotranspiration will tried to be removed by surface soil evaporation.

I will do a drawing about these and post in evapotranspiration wiki.

Sorry for the different messages between me and Eduardo. Please try these to check that it can be done evaporation without vegetation and we will talk


EVAPOTRANSPIRATION_METHOD is keyword to see how evaporation and transpiration will act in soil water.
EVAP_METHOD is evaporation not in soil but evaporation only for water that is in surface runoff or leafs.


Hope it helped.
David

epelde.ane@gmail.com
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Posts: 172
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Re: Evapotranspiration

Postby epelde.ane@gmail.com » Fri Dec 23, 2011 14:09

Hello,
With EVAPOTRANSPIRATION_METHOD:1 it just give me the option of setting EVAP_METHOD:3, which meant that there wont be evaporation. And I would like to set a configuration to process evaporation process from soil and in case that there isnt water on soil, in ground. But not from vegetation because there isnt any yet.
What configuration do you recommend in that case?

davidbrito
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Posts: 189
Joined: Thu Jan 01, 1970 00:00

Re: Evapotranspiration

Postby davidbrito » Mon Jan 16, 2012 16:51

Hello,


"With EVAPOTRANSPIRATION_METHOD:1 it just give me the option of setting EVAP_METHOD:3, "
This option EVAPOTRANSPIRATION_METHOD:1 says that all evapotranspiration is met in vegetation roots so if you have roots you have transpiration if not, not.

The best woul be EVAPOTRANSPIRATION_METHOD:2 and it tries to take the water from roots but also from soil.


David


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