Water Footprint and AWY

Science, Research & Data
1

Hello, I am doing research on the water footprint of dairy livestock. The general formula for estimating the water footprint is:
blue water (surface and ground water) + green water (rain) + grey water (waste or sewage water) = total footprint.
The green water footprint refers to consumption of green water resources (rainwater in so far as it does not become runoff). I ran AWY model to estimate the flow in the watershed, and I wonder whether someone has an idea on how to relate it with the green water use in any definite area. I mean, when running the model does the final result of water flow consider the green water use from forage/grass consumed by grazing animals, according to the LULC, soil, rain and everyother variable considered by InVEST?
Thanks for your advise, I am quite confused about this.

2

Hi @evselem -

I would say that the AWY model provides information about blue water in general (surface + baseflow). As the User Guide says:

The model does not differentiate between surface, subsurface and baseflow, but assumes that all water yield from a pixel reaches the point of interest via one of these pathways.

While it does include baseflow, AWY doesn’t include groundwater from aquifers, so if groundwater is important to consider separately you’ll need a different model.

AWY also doesn’t provide a “retention” focused result, other than AET, which shows water uptake by the different land cover types. Greater AET does mean less runoff from each pixel. And because you provide Kc values for each land cover type, they will differ in the amount of runoff that comes from forest versus pasture. But it doesn’t separate out recharge, or take into account vegetation use of water that flows it to from upslope, etc. Nor does it directly consider the removal of the water by animals grazing the land cover.

~ Stacie

3

Hi Stacie,

Thanks for your reply. I’m still in doubt with some issues:

  1. extraction of groundwater or surface water is not an issue, so I am not concerned with this
  2. the point that I need to figure out is regarding the rain water (green water) consumed by cattle from the grass/pastures and transferred to milk or beef. So it is water extracted that does not goes back to the watershed.
  3. The AWY model guide, in its “Consumptive water use” section", suggests that “For agricultural areas, water used by cattle or agricultural processing that is not returned to the watershed must be considered.”
  4. As I understand, the actual evapotranspiration equals the consumption of green water from every LULC class, so is it correct to consider the evavotranspiration of pastures as the green water consumption in the watershed?
  5. If not, can you suggest a source of information to estimate this consumption and include it in my calculations as the water demand mentioned in the guide:

" Water Demand Table (CSV, optional): A table of water demand for each LULC class. Each LULC code in the LULC raster must have a corresponding row in this table.
Consumptive water use is that part of water used that is incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the watershed water balance."

Thanks for your advise

ENrique