Re: [QSWAT+ User Group] an error occurred simulate pesticide with swat+

[Paulo Amaral]

Hello everyone,

I am writing to this thread because I am also currently working with the SWAT+ Editor for my doctoral thesis and need to simulate the use of pesticides, specifically Aatrex.

I would be very grateful if anyone could share the procedures or steps necessary to successfully implement pesticide application in the SWAT+ Editor, as I am also looking for guidance on this topic.

Thank you in advance for any assistance you can provide.

Best regards,

Paulo

Em qua., 27 de ago. de 2025 às 13:11, 邓钧 <dengj...@gmail.com> escreveu:

Hello everyone, I want to use SWAT+ to simulate pesticide application in a watershed, but after I added the pesticide application in the management schedules, an error occurred as shown in the picture.

Can anyone help me? I would greatly appreciate it. Here is my TxtInOut file.

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[Paulo Amaral]

 TxtInOut.zip

Dear SWAT+ User Group,

I am encountering a persistent forrtl: error (72): floating overflow when attempting to simulate atrazine (aatrex) application in SWAT+ Editor (version 3.0.8, SWAT+ rev. 61.0.1). The error consistently points to the RES_PEST routine in res_pest.f90.

Here's a breakdown of the problem and the troubleshooting steps I've already taken:

Initial Problem & Troubleshooting:

Initial floating overflow error: The error first appeared when I had Amount of pesticide in water at start of simulation (kg/ha) set to 1 in the Constituents > Pesticides > Water Initializations section. This was identified as a potential division-by-zero issue at the start of the simulation.

Correction 1 (Water Initializations): I corrected this by setting Amount of pesticide in water at start of simulation (kg/ha) and Amount of pesticide in the benthic zone at start of simulation (kg/ha) to 0. (See Screenshot 1).

Result: The floating overflow error persisted when running the simulation with an actual amount of atrazine applied (e.g., 0.5 kg/ha) in the Management Schedules.

Further Diagnosis:

Testing Application Amount: I found that if I set the Amount applied (kg/ha) to 0 in the pest - pesticide application operation within my Management Schedules, the model runs without error. This indicates the problem is specifically triggered when a non-zero amount of pesticide is applied.

Checking Pesticide Parameters: I then reviewed the detailed physicochemical parameters for aatrex under Databases > Pesticides (See Screenshot 2).

I noticed that the solub (Solubility of chemical in water) parameter was set to 33 mg/L (ppm), while the Recommended Range was 0-1. This seemed like a strong candidate for the error.

Correction 2 (Solubility Parameter): I changed the solub value from 33 to 0.001 (a value within the recommended range).

Result: The floating overflow error still persists when running the simulation with 0.5 kg/ha of atrazine applied (on Jan 15th, Year 1 of rotation) and solub set to 0.001. (See Screenshot 3 for the error message, and Screenshot 4 for the current application schedule).
Current Situation:

The model runs fine if no atrazine is applied (Amount applied = 0). The error occurs specifically when a non-zero amount is applied, even with initial water concentrations at zero and solub within the recommended range. The application is scheduled for a fixed date (January 15th, Year 1 of rotation).

I suspect there might be an issue with other physicochemical parameters, an interaction with environmental conditions on the application date, or a potential bug in this specific SWAT+ revision when handling pesticide application calculations.

Any insights or suggestions from the community would be appreciated.

Thank you,

Paulo Amaral