meaning of v42_irrig_eff

[jansteinhauser]

Hello everyone,

Very excited to work on/with MAgPIE but still getting the hang of it. So, I may have a few basic questions here and there. The first one is a sanity check;

In Water Demand, the variable v42_irrig_eff is described as "correspond[ing] to the amount of water that is used inefficiently in the irrigation process".

However, the way I understand the demand equation, the variable describes the share of the total (crop) water demand that actually reaches the crops, while, for example, in the global static scenario with, by default, v42_irrig_eff <- 0.66, 34% of water is used inefficiently and lost without effect. Meaning, at 66% efficiency crops would have an actual demand of ~151% of their base demand.

This, in my understanding, is the exact opposite of the variable description quoted above. So, my question is: Is this interpretation correct or do I misunderstand the variable description, equation, or both?

Thank you and all the best,
Jan

Edit for clarity, as I was imprecise when calling the global static efficiency the default (meaning the default efficiency in that scenario). It was just intended as a calculation example.

[abhimishr]

Hi Jan,

The default realization of water demand module (42_water_demand) seems to be agr_sector_aug13.

There, v42_irrig_eff is always fixed to a certain value depending on s42_irrig_eff_scenario (see here).

Default s42_irrig_eff_scenario is set to 2 (from here and here) and is described as "regional static values from gdp regression".

In case you have a MAgPIE run available. You can plug in the fulldata.gdx file and check the values using following code snippet in an R environment:

library(magpie4)
gdx <- "path/to/fulldata.gdx"
irrig_eff <- collapseNames(readGDX(gdx,"ov42_irrig_eff")[,,"level"])
irrig_eff

As s42_irrig_eff_scenario is set to 2, every MAgPIE cluster would get a specific value based on the regression calculation from here. A global value of 0.66 is only used if s42_irrig_eff_scenario is set to 1.

From the documentation link, it looks like this was generated from in-code documentation which was last updated quite a long time ago. Meanwhile, I am tagging our irrigation experts @FelicitasBeier and @vartika271987 here as they would be the best ones to clarify it further.

Hope this helps!

[jansteinhauser]

Hi Abhijeet,

Thank you for your explanation. I've edited my initial question as I realized my wording was quite imprecise. Your explanation was definitely helpful to drive home the differences in the scenario choices but my question was more basic than that. Basically, I just wanted to ensure that I understood the meaning of the variable correctly.
To me, based on the equation, it's the share of water that reaches the crops. However, the text reads to me as if it was the share of water that does not.

Thanks again!

[FelicitasBeier]

v42_irrig_eff(j) indeed refers to Irrigation efficiency (as defined in the declarations). It is the share of water that is actually used by the crop(s).
To calculate water demand for agriculture we calculate water use of crops (areawater_requirementsirrigation_efficiency) + water use of livestock (livestock_production * water_requirements_of_livestock) (as you can see in the respective equation).
Losses of water that occur through transport from source to field are not consumed by the crops and therefore should not be accounted as agricultural water use.

I will have a look at the wording of the in-code comments again. It seems that this might have been phrased misleadingly. The variable v42_irrig_eff indeed captures inefficient water use (which I assume the author wanted to say here), but it does not correspond to it, in my view.
You can also have a look at the realization.gms of the respective modules for further explanations.

Hope this was helpful.

[jansteinhauser]

Thank you for clarifying, seems I got it right then.
I can't mark your response as answer. Could you repost your text as direct answer to my initial question please?

Thanks again!

[FelicitasBeier]

v42_irrig_eff(j) indeed refers to Irrigation efficiency (as defined in the declarations). It is the share of water that is actually used by the crop(s).
To calculate water demand for agriculture we calculate water use of crops (areawater_requirementsirrigation_efficiency) + water use of livestock (livestock_production * water_requirements_of_livestock) (as you can see in the respective equation).
Losses of water that occur through transport from source to field are not consumed by the crops and therefore should not be accounted as agricultural water use.

I will have a look at the wording of the in-code comments again. It seems that this might have been phrased misleadingly. The variable v42_irrig_eff indeed captures inefficient water use (which I assume the author wanted to say here), but it does not correspond to it, in my view.
You can also have a look at the realization.gms of the respective modules for further explanations.

Hope this was helpful.