fix: enable biogenic CO2 calculations to resolve constant FcRespi output (#245)

[sunt05]

Summary

• Fixes FcRespi output is constant  #245 - FcRespi output was constant throughout simulation days
• Re-enables the biogenic CO2 calculation module that was completely commented out
• Ensures FcRespi now varies with temperature as expected

Problem

The SUEWS_cal_BiogenCO2 subroutine in suews_ctrl_driver.f95 was entirely commented out, preventing any biogenic CO2 calculations. This caused FcRespi (respiration flux) to remain at its initialized value of 0.0 throughout simulations.

Solution

1. Uncommented the biogenic CO2 calculation code:

   • Restored the SUEWS_cal_BiogenCO2 subroutine definition
   • Added call to SUEWS_cal_BiogenCO2 in the main simulation loop after anthropogenic emissions

2. Fixed compilation errors:

   • Corrected module import: sfc_resist → resist_module for SurfaceResistance
   • Fixed case sensitivity: ANTHRO_EMIS_STATE → anthroEmis_STATE
   • Added missing imports: HYDRO_STATE and SUEWS_SITE

3. Verified the fix works:

   • FcRespi now varies with temperature when resp_b parameter is non-zero
   • Total CO2 flux (Fc) correctly combines anthropogenic and biogenic components

Testing

✅ Fortran code compiles successfully
✅ Python tests demonstrate varying FcRespi output when appropriate parameters are set
✅ Backwards compatible - no breaking changes to existing functionality

Important Note on Sample Data

The default sample data has resp_b = 0.0 (temperature sensitivity coefficient), which makes FcRespi appear constant even with the fix. This is expected behavior - when resp_b = 0, the equation EXP(resp_b * T) always equals 1, resulting in constant respiration.

Users should ensure their input parameters have non-zero resp_b values for temperature-dependent respiration.

Test Results

With manually adjusted parameters (resp_b = 0.08, vegetation fraction = 30%):

• Before fix: FcRespi = 0.0 (always)
• After fix: FcRespi varies from 0.703 to 0.721 μmol m⁻² s⁻¹ with temperature

Related Issues

• Closes FcRespi output is constant  #245