Water Yield: per pixel interpretation.

Hello,

I'm using the Water Yield model (in addition to other InVEST models) to determine which parcels within a given watershed provide more ecosystem services (ESs), including water production. One step of this study would be to assign levels of ESs to these parcels. However, the InVEST manual says that the output of this model should not be interpreted at the pixel level.

In this case, can I still use per pixel values and assign levels of water production to each parcel (some of them may contain only a few pixels) or I should calculate the average of water production per pixel within a subwatershed and assign this same level to all parcels within this subwatershed? 

Thank you!
Fabio

Comments

  • CharChar Member
    hi,

    I saw some of the researches published in the science of the total environment and ecological indicators directly used per pixel values of water yields calculated from the WY model as the supply of ecosystem service.
  • Hello,

    I've seen some studies using pixel values to sustain their point as well. However, I'm not sure if this approach is acceptable according to the manual's instructions. 

    Thanks for answering! 
    Fabio
  • swolnyswolny Member, NatCap Staff
    Hi Fabio -

    You're correct that we recommend using the results at the sub-watershed level, since that's what the underlying equations were made for. Since no routing is done in Annual Water Yield, it is also fine to aggregate the pixel results into some other polygon like parcels instead of sub-watersheds. But I see how it gets questionable when the parcels only contain a few pixels. Is it the case that all of the parcels are that small, or are most of them larger, with just a few small ones? 

    ~ Stacie
  • Stacie,

    I have both small and big parcels. Hard to tell the proportion, but I'd say the parcels that really matter are overall big (more than 10 acres, if you call them big). What would be the threshold to use per pixel values or not? In terms of acreage of a polygon. Any suggestion?

    Thanks,
    Fabio
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