Guidance Needed on SWAT Calibration Without Observed Streamflow Data

[bharadwaj mandala]

Dear SWAT+ Community,

 I am seeking some guidance regarding model calibration.

My study area does not have a USGS streamflow-gaging station, and therefore I do not have observed streamflow data directly available for my watershed. I would like to calibrate the SWAT model for streamflow and subsequently use it for sediment and water-quality simulations.

I would appreciate any suggestions on how to approach calibration in this situation. Specifically:

• Can observed streamflow data from a nearby USGS station be used for calibration if it is outside my watershed?
• What are the recommended approaches for transferring or regionalizing flow information from a nearby watershed?
• Are there any alternative sources of observed or estimated streamflow data that could be suitable for SWAT calibration?
• What would be the best approach if no suitable nearby gaging station is available?

Any guidance, references, or examples of similar applications would be greatly appreciated.

Thank you in advance for your help.

Best regards,

Bharadwaj Mandala

PhD Student

Department of Civil and Environmental Engineering

Rowan University

214-(516)-9958

mand...@rowan.edu 

linkedin.com/in/bharadwajmandala

[Natalja C.]

All of the points you raised are extensively discussed in the hydrological modeling and SWAT literature. These are very common questions when dealing with ungauged basins, but there is no "one size fits all" solution. The right choice depends heavily on your watershed's size, dominant hydrological processes, physiographic similarity to neighboring catchments, and intended modeling objectives.

I strongly encourage you to conduct a literature review on standard techniques before deciding on an approach:
-  Look into physical similarity, spatial proximity, and regression-based regionalization methods.

-  When streamflow records are absent, studies often turn to remote-sensing products (such as MODIS/GLEAM evapotranspiration or GRACE/SMAP soil moisture and terrestrial water storage) or regional water balance estimates to constrain model parameters.

- utilizing other "soft" data: crop growth and production, biomass estimate, etc.

Here is your "SWAT approved" source of literature: https://swat.tamu.edu/publications/

Examine the physical characteristics of your watershed alongside potential donor basins, review how others have handled similar constraints, and define a clear strategy that best fits your study area.  

Best,

Natalja