Commanding SWAT to use inputs from .bsn OR .hru/.sno files?

[Steven Jepsen]

Hi All,

Is there a flag that tells SWAT whether to use a parameter from the .bsn file or a .hru file? For example, ESCO is specified in both the .bsn file and .hru files. Is it possible to tell SWAT to only use the ESCO value in the .bsn file? If so, how? Just leave the value in the .hru file blank? Or maybe use "-99", etc? I couldn't find anything on this in the input/output documentation.

I have a similar question for the snow parameters. My understanding is that SWAT automatically uses .sno inputs if those files are present (and the .sno filename is listed in the .sub file, which may serve as a flag to SWAT). I've verified this through testing; however, I've gotten some strange results and am doing more QA/QC testing now. 

Still I am curious whether there is a flag that tells SWAT to use a parameter value from the .bsn file, such as "-99" or blank values in the .hru or .sno files. Seems like there would have to be.

Thanks,

Steven Jepsen

[Jim Almendinger]

Steve --

For esco, I'm pretty sure the hru file has priority -- if esco is specified (>0) in the hru file, SWAT uses it; if not it reverts to the esco specified in the bsn file.  I think esco=0 in the hru file is enough to have SWAT ignore it and use the bsn esco value -- i.e., I don't think it has to be a blank.  So, it's pretty much exactly as you had figured out. 

I don't know about the sno files, but I suspect you're right there as well.

-- Jim

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From: "Steven Jepsen" <thesj...@gmail.com>
To: "SWAT-user" <swat...@googlegroups.com>
Sent: Friday, April 29, 2016 12:43:15 PM
Subject: [SWAT-user:6173] Commanding SWAT to use inputs from .bsn OR .hru/.sno files?

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Dr. James E. Almendinger
St. Croix Watershed Research Station
Science Museum of Minnesota
16910 152nd St N
Marine on St. Croix, MN  55047
tel: 651-433-5953 ext 19

[Steven Jepsen]

Jim,

OK, that makes sense. Thanks. Just insert an invalid value in the .hru file to have SWAT use the .bsn file. I'll keep this in mind. I guess in the end I just need to experiment to know for sure.

Steve

[R Srinivasan]

Yes, if sno file exist it will be given priority before using bsn files.

Srini

[Steven Jepsen]

Srini,

I am finding some discrepancies between models using snow parameters from the .bsn file and snow parameters from the .sno files. I ran a simple test case today using 2 models: (1) one model using 11 different SFTMP values specified in the .bsn file, (2) a different model using 11 different SUB_SFTMP values specified in the .sno files. Both models were run in SWAT-CUP 5.1.6.2. I made sure that both models being compared used the same snow parameter values, which were spatially distributed across subbasins uniformly.

The models should have matched one another, if I set things up correctly. The models did not match one another when SUB_SFTMP was > ~ 0.0. The results from case 1 looked physically reasonable, the results from case 2 did not. Case 2 stream discharge values are all identical when SUB_SFTMP is < ~ 0.0. I have the results in spreadsheets and all of the input/output from SWAT-CUP.

Have you heard of any issues relating to this discrepancy I'm describing? I saw a posting here from about 4 years ago, which I replied to today, where someone was having some related issues. There were no replies to that post (except for mine).

I am going to do a few more targeted runs over the weekend to make sure I'm not doing something silly. I'll post again after that time.

Thanks,

Steve 

Thanks,

Steve 

[Steven Jepsen]

Correction...

The two cases did not match when SUB_SFTMP was < ~ 0.0. To restate, something looks wrong with the output from models with SUB_SFTMP < 0.0 (values all the same).

[andreasculbertson]

Looking at the source code (readsno.f line 66 and readsub.f line411, rev629) it looks like the way SWAT checks for an invalid value for SUB_SFTMP in either the .sno or .sub files is checking if the value is < 0. In this case, it reverts to the .bsn value for SFTMP. Seems like a bug since SUB_SFTMP should definitely be allowed to be negative. Can you confirm if this happens?

Andreas

[Steven Jepsen]

Andreas,

Yes, this is consistent with output from my test cases. The model with subbasin snow parameters looked okay when SUB_SFTMP > ~ 0.0, not okay otherwise. As you stated, SUB_SFTMP should be allowed to go negative (suggested lower limit in documentation is -5.0 deg C).

Nice find! Thank you for checking this.

I guess this means that I'll have to make do with watershed level snow parameters, at least for now. That is too bad--I think my models could have been better calibrated using subbasin level snow parameters.

Thank you again.

Regards,

Steve

[Steven Jepsen]

Dear All,

I just wanted to follow up once more on this. I did a few more tests and confirmed that the pattern in my model outputs match what Andreas described from the source code. This bug should hopefully be fixed soon.

Thanks,

Steve 

 

On Monday, May 2, 2016 at 12:12:12 PM UTC-7, andreasculbertson wrote:

[Sandeep Rana]

Hello Steven and all,

Based on conversation here, do I need to use snow parameter at basin level (.bsn) to calibrate my model?

Also, I have snowfall in whole large basin (though it is higher in mountain) , I believe using snow parameter in .sub/.sno files,will create more uncertainty. I have elevation band (in mountains) too in my model.

Thanks for your time,
Sandeep

[Nigatu Mikiyas]

please dear SWAT communities, how SWAT model computes the initial soil moisture (SWo) in general water balance equation?