Guidance Needed for Forest-to-Silvopasture Land-Use Scenario in SWAT+

[Gafar Agunbiade]

Dear SWAT+ Development and Support Team,

I am working on a land-use change scenario in SWAT+ to evaluate the hydrologic and water-quality effects of converting forest land to silvopasture.

Specifically, I want to convert all HRUs assigned to frst_lum within subbasin 9 to a custom land-use definition, spst_lum. For spst_lum, I created a plant community containing FRSE, rye, and bermudagrass, along with a management schedule for the required silvopasture operations.

I first attempted to implement the conversion by manually replacing frst_lum with spst_lum for the targeted HRUs in hru-data.hru. However, when the input files were rewritten or the simulation was run through SWAT+ Editor, the HRUs reverted to frst_lum. I assume this occurs because the Editor regenerates the files using the land-use assignments stored in the project database.

I then attempted to implement the conversion using a decision table named “Scenario Land Use” and created a scen_lu.dtl file. I adapted the structure from examples in the SWAT+ datasets library and attempted to assign the targeted forest HRUs to spst_lum. However, importing the decision table produced the following error:

Traceback (most recent call last): File "swatplus_api.py", line 186, in <module> File "actions\import_export_data.py", line 141, in import_csv File "fileio\decision_table.py", line 52, in read File "fileio\decision_table.py", line 66, in read_table ValueError: invalid literal for int() with base 10: 'hru' [PYI-36496:ERROR] Failed to execute script 'swatplus_api' due to unhandled exception!

I am also experiencing an issue with the management schedule. The operations I created are present in management.sch, but they do not appear in mgt_out. Therefore, I cannot confirm that the schedule associated with spst_lum is assigned correctly or that the operations are being triggered during the simulation.

I would appreciate guidance on the following:

1. What is the recommended procedure for converting all frst_lum HRUs in subbasin 9 to spst_lum?
2. Should this conversion be made in the SWAT+ project database before writing the input files, or can it be implemented dynamically during a specified simulation year using a decision table?
3. If a decision table can be used, which action, object type, and file structure are required to change an HRU from one land-use definition to another? Can the decision table target HRUs using both subbasin and current land-use criteria, as shown below?

Subbasin: 9 Current land use: frst_lum New land use: spst_lum

4. Can one decision table update all qualifying HRUs, or must each HRU be listed individually?
5. After changing an HRU to spst_lum, will SWAT+ automatically apply the plant community, management schedule, curve number, and other parameters linked to that land use, or must these components be assigned separately?
6. Which database tables or input files should I inspect to verify the following connections?

HRU → spst_lum → plant community → management schedule → management operations

7. Why might operations listed in management.sch not appear in mgt_out? Does the schedule’s presence in management.sch confirm that it is assigned to an active HRU, or can an unassigned schedule still be written to the file?
8. Does mgt_out need to be enabled separately in the print settings, and does it report only operations that are successfully triggered during the simulation?

My intention is to simulate a physical conversion from forest to silvopasture, not simply to add management operations to the existing forest land use. At present, I cannot confirm that the targeted HRUs are being converted or that the custom silvopasture management schedule is being executed.

An example showing how to convert selected HRUs to a custom land use and correctly connect the new land use to its plant community and management schedule would be very helpful.

The TxtInOut folder, screenshots, decision-table files, and other relevant scenario inputs are available at the following Google Drive link:

https://drive.google.com/drive/folders/1NizIyI2o3Rqi9oHDn3dD3hapXixDXu6H?usp=sharing

Thank you for your assistance in identifying what may be misconfigured and for advising me on the appropriate procedure.

Best regards,
Gafar Agunbiade