Hii,
I am working with the SWY model. In my research area I only have SHG classes 3 and 4, in that case, will my biophysical table have CN_C and CN_D only?
Also, I am trying to do sensitivity analysis changing alpha and beta values as done in other research papers, but there is no change in result. I am wondering is it because of my SHG input data. I am using SHG data from DAAC.
Regards
-Sreejita
Hi @Sreejita -
I’m pretty sure that you will still need to provide columns in the biophysical table for CN_A and CN_B, even though they are not in your hydrologic group map. You can just give values of 0 for those columns.
And I don’t know enough about the alpha and beta parameters to comment on that, although it does seem like they should have an effect on the result. Are the results exactly the same, or are there some differences? It isn’t unusual for an area to only have 2 or 3 of the SHG values within them, and I don’t think that should be the cause of there being no change in results from changing the alpha and beta parameters.
~ Stacie
Hi @swolny
Thank you for your response on the hydrologic group.
The results are the same, when I change my alpha values from 1/12 to 1/3 and 1/6 and for beta I have changed values from 1 to 0.5 one at a time.
I am unable to solve this issue.
If the results are exactly the same, I wonder if it has to do with equation 92 in the User Guide.
It may be the case that PET is always the minimum value, so AET is always assigned to PET, and alpha and beta are not used. Can you check this by comparing your AET and PET rasters?
~ Stacie
Shall I share my input and output files to cross-check?
@Sreejita we encourage people to do their own investigation first, to get a deeper understanding of how the models work, and how to troubleshoot. In this case, I’m noticing that we haven’t made it easy to compare monthly AET with monthly PET, because we aren’t outputting the intermediate monthly AET or PET results from equations 92 and 93, which I think we should do.
I’ve just asked about adding these to the results in a future InVEST release, but in the meantime, you could calculate monthly PET using equation 93 along with the monthly kc_* rasters in the intermediate folder. Then add those together and see how they compare with the annual AET raster that is also in the intermediate folder. If they are the same, that is an indication that the model found all of the monthly PET values to be the minimum tested for in equation 92. Hopefully in the future we’ll provide the outputs to make this comparison easier.
~ Stacie
