Water yield resolution issue

I have a question about water yield resolution

sample two type
prec : 1km (world clim data)
pet :1km (world clim data)
drrl : national data (10m, 30m)
pawc : national data (10m, 30m)
lulc : national data (10m, 30m)

Difference between 10m and 30m results
I don’t know why.
What should I base on?

Hello @kims -

Can you provide more detail about the question you’re asking? Did you run the annual water yield model multiple times using different input raster resolutions (10m and 30m) and get different results? Which version of InVEST are you using? How different are the results? Is it a small difference, or is the difference very large? Are you looking at the pixel-level results, or subwatershed level results? Are the patterns different, or just the values?

You may use whatever resolution inputs you like, but the model will resample all of the raster inputs to be the same resolution as the LULC. Resampling may slightly change some of the values for precipitation, PET, soil depth and PAWC, so if you’re seeing a small difference in results that may be why. If you’re seeing a very large difference, like an order of magnitude, then that’s surprising. I don’t think there’s anything in the biophysical part of the model that calculates based on area (although the software team can correct me if I’m wrong) so I would expect similar results, even if your LULC changes resolution.

However, if you are including water scarcity, it does involve area, so different resolutions of LULC can affect the results in that case. Also, if the 10m and 30m LULCs are different (have different classes, or different patterns of LULC) then you’ll see a difference in the results.

~ Stacie

Sorry for the rather rough question.
I turn the model again
I found out my question was wrong.
wy_result.csv (5.6 KB)
Tables of the results for resolution show no significant difference.
Attach a table.
Thank you for your detailed response.

I’m not familiar with English, so I write through Google Translate.
Hope to understand and thank you.

No problem, @kims, I just used Google Translate to write to people in Spanish, and I hope they understand me too, and I hope that you can understand my response. :slight_smile:

I would expect that there is no significant difference, if the input layers are the same, only resampled to different resolutions. As I said before, this model is not doing calculations based on resolution. For example, the value for water yield is in mm, not volume, not mm/ha or anything involving the area of each cell. The slight differences that you do see are probably due to the model resampling precip, PET etc to the resolution of the LULC. It is interesting that there’s more of a difference in water yield between 10m and 30m than between 30m and 50m/70m/100m, but still, as you say, the difference is small.

You could try resampling all of your input layers to be the same as the LULC (and aligned to/snapped to the LULC raster when you resample) before entering them into the model (so the model probably won’t do the resampling process again) and see how that affects the results.

If I’m still not understanding your question, apologies, and please let me know.

~ Stacie