Discrepancies between Hydropower model outputs between versions 2.5.6. and 3.3.3.

Hello,

I have a question regarding the Water yield model in InVEST version 2.5.6. and 3.3.3.

I have run the model in both versions using exactly the same data/parameters and I obtained quite different results. In general, version 3.3.3. returned much lower water yield than version 2.5.6. (the ArcGIS toolbox version). To give you an example, from the pixel maps wyield output, it appears that paved surfaces did not generate any run-off according to version 3.3.3, and in version 2.5.6 run-off from these surfaces was substantial. Run-off from all remaining LULC classes (grassland, arable, woodland, etc) was again much lower in version 3.3.3., which appears a bit counter-intuitive.

I was wondering whether there are any reasons from the model's operational point of view for these differences? Looking at the user guides for both versions, it appears that the model principle has not changed so in theory both versions should return comparable results. Or could this be a matter of using certain parameters in the wrong order of magnitude in the 3.3.3. model?

Any help/insights on this will be greatly appreciated as I would like to understand the reasons behind the differing outputs!

Kind regards,
Joanna 
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Comments

  • RichRich Administrator, NatCap Staff
    Hi Joanna, v2.5.6 was a very old version of InVEST. Although that was years ago, I'm sure we've fixed many bugs since then. But if you're unsure of results, I'd be curious about the pavement example you're giving. Could you dropbox me your datastack to richsharp@stanford.edu and I can take a look to see if it's a software issue? 
  • RichRich Administrator, NatCap Staff
    Hi @joaz, I ran the model on your data and looked it over. I haven't gone back and looked at the 2.5.6 user's guide, but I since that model we've added an "LULC_veg" field to the model which selects which AET equation (eq 1 or 2) to use given the appropriate landcover context. This would explain why you're seeing a different runoff on paved surfaces since in your biophysical table you have those set to non-vegetation. And in my run I see it all goes to AET on the paved surfaces. 

    At any rate, looking over your data and run, it looks like everything is working correctly from a software perspective. And knowing this, does this seem to cover the issue for you?

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