SWAT+ Toolbox v3.2.0: DDS Calibration Runs Successfully but NSE/KGE/RMSE/PBIAS Display as NaN

[Khybeer]

The Problem

DDS calibration in SWAT+ Toolbox appears to run successfully:

• hydrographs are generated correctly,
• observed and simulated flows are plotted,
• KGE optimization progresses normally,
• best KGE reaches approximately 0.687.

However, the calibration statistics table consistently displays:

• NSE = NaN
• KGE = NaN
• RMSE = NaN
• PBIAS = NaN

despite the hydrograph plotting correctly and KGE clearly being optimized internally.

The issue persists after:

• verifying the observed CSV formatting,
• confirming the outlet channel,
• refining parameter ranges,
• and stabilizing snowmelt parameter combinations.

Observed data checks:

• Header format: Date,Flow
• Monthly end-of-month dates
• No missing values
• No duplicate records
• Continuous monthly series (84 records)
• Perfect overlap with simulation period

Current calibration settings:

• DDS algorithm
• KGE objective function
• 800 iterations
• 4 parallel processes
• Include current parameter values = YES

Current calibration parameters:

• cn2
• alpha
• lat_ttime
• revap_min
• chk
• snomelt_max
• snomelt_min
• snomelt_lag
• snomelt_tmp

Steps to Reproduce

1. Prepare monthly observed streamflow CSV using end-of-month dates.
2. Run SWAT+ Toolbox calibration using DDS and KGE.
3. Calibration progresses normally and hydrograph is displayed.
4. Best KGE value updates during optimization.
5. Final statistics panel displays NaN for NSE, KGE, RMSE, and PBIAS.