Support Request about Calibration

[kingstn]

Dear WRF-Hydro Community,

I'm currently working on my first WRF-Hydro simulation and have begun exploring the calibration process. I've encountered a few challenges and would be grateful for your guidance.

Specifically,

1. I noticed that the simulated outputs (e.g., *CHANOBS_DOMAIN2, *CHRTOUT_DOMAIN2, and Route_Link.nc) do not reflect the exact gauge locations I specified.
2. I want to calibrate the model at a single observed gauge station. Is this feasible within the WRF-Hydro framework? If so, is there a recommended approach (manual or otherwise) to achieve this?
3. Additionally, If there are any critical preprocessing steps or setup considerations I should be aware of before starting the calibration, I would appreciate any advice or resources you can share.

For context, I've included plots comparing the observed data with the WRF-Hydro outputs mentioned above.

Thank you very much for your time, and I truly appreciate the valuable support.

[Arezoo RafieeiNasab]

Hello, 

May I ask what you mean by the simulated outputs not reflecting the exact gauge location? Do you mean the location of the gauges is not specified right in the Route_link.nc file when you did the pre-processing, or do you mean the simulated flows are not close to the observation. I thought you mean the latter, but wanted to confirm that is the case? 

I assume you are using the reach based routing given you are referring to to the Routelink, correct? I usually look at the CHANOBS files for verification against the gauge, the feature_id in the CHANOBS file should match the one in the Routelink. And yes, you could calibrate the model at a single gauge location. Here is the github repo for calibration: https://github.com/NCAR/PyWrfHydroCalib . There is documentation for it available here: https://github.com/NCAR/PyWrfHydroCalib/tree/master/docs that you could review and find out more about how it is actually done. 

Let me know if you have any follow up question. Thanks!

Arezoo

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Arezoo Rafieei Nasab, Ph.D.

Project Scientist II

NCAR Research Applications Laboratory

are...@ucar.edu

[Negusu Tarekegn]

Hi Arezoo,
Thank you for your assistance; I truly appreciate your guidance!
To clarify what I meant: the gauge points don’t fall exactly on features in RouteLink.nc. I matched each gauge to the nearest feature_id in RouteLink and used those nearest links for comparison. 
With that approach, the simulated flows at several sites do not match the observations.

Yes, I’m using reach-based routing. So, matching gauges to the nearest RouteLink feature_id is the right approach?

If you notice anything incorrect in my setup, I have attached the RouteLink and gauge stations file.

Thanks.

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[Kevin Sampson]

Negusu,

Choosing the nearest route_link feature to your gage is not always the correct approach. Care must be taken to ensure that the location of the gage on your WRF-Hydro reach network represents the hydrologic location of the gage in reality. Gages are often placed above or below confluences, which do not always correspond to the confluences in the modeled network. The modeler must review each gauge placement in the context of the hydrologic network represented in the model and make adjustments as necessary.

Kevin

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[Negusu Tarekegn]

Hi Kevin,

Thank you for the clear guidance.

I corrected the gauge mismatch as per your advice.

One more thing, for calibration, I did a four-month run: one month for spinup, two months for calibration, and one month for validation. 

Is that window adequate, and would 'PyWrfHydroCalib' be suitable for a calibration period of this length? If not, may I apply manual calibration?

Thanks again for pointing me in the right direction.

Best regards,
Negusu

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[Kevin Sampson]

Negusu,

It does not sound to me as though you have allowed enough time for spinup, calibration, or validation. This will depend greatly on the hydroclimatology of your region of interest, but it is common to use multiple years for spinup and for calibration. This can sometimes be a single year of forcings run multiple times if you do not have sufficient forcings to support a long spinup. Remember that the model is starting from a 'cold start' with default parameters and states. You will need to give the simulation enough time to 'warm up' and reach a kind of equilibrium. Surface water might spin up quickly while subsurface and deep groundwater takes much longer.

Thanks,

Kevin

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[Negusu Tarekegn]

Thank you, Kevin, for the guidance.

You’re right. I likely haven’t allowed enough time for spin-up and calibration. 

My primary constraint is computational resources, since I’m using WRF output as forcings. I’m currently running WRF-Hydro with 3-hourly forcings. 
To extend the period, would it be reasonable to switch to 6-hourly forcings (or repeat a single forcing year several times) for spin-up and then return to 3-hourly for calibration/validation? 
In your experience, does WRF-Hydro behave reliably with 6-hourly forcings?

Thanks again for your help.

Best regards,
Negusu

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[Kevin Sampson]

Negusu,

I am not in a good position to comment, as I mostly run simulations with hourly data. I am not sure what potential issues may be introduced by performing spinup and calibration/validation using different time-stepping. Perhaps others may comment on their experiences.

Kevin

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