High CO2 conctration

[Aimen Sattar]

Hi everyone,

I’m conducting a scenario analysis using SWAT+ and have included dynamic atmospheric CO₂ concentrations. However, I’m facing challenges in how to update the co2_hi and bm_e_hi parameters in the plant.plt file.

There seems to be limited guidance in the literature on appropriate values for these parameters, particularly under high-CO₂ scenarios. While some experimental studies provide yield responses to elevated CO₂, they typically do not extend to concentrations as high as those projected in SSP5 for 2100 (up to 1200 ppm). I also haven’t found a clear method for calculating bm_e_hi based on those yield data.

Additionally, I’m unclear on how SWAT+ (and the underlying EPIC model) handles CO₂ concentrations that exceed the co2_hi threshold. In reality, many crops benefit from increasing CO₂ up to an optimum, beyond which yield gains plateau or even decline. Does SWAT+/EPIC account for this non-linear or saturating response?

I’d be very grateful for any advice or resources on this topic, especially relating to how to set or calibrate co2_hi and bm_e_hi under future climate scenarios.

Thank you,
Aimen

[Natalja C.]

Hello,

You are not finding these values because there is currently insufficient literature or supporting studies for the models. In fact, the issue you've raised would be a perfect introduction for a relevant research paper or even a PhD topic.
The current limits in SWAT+ are based on underlying studies conducted several decades ago. To our knowledge, there is not enough recent science to justify further developments in this regard. Thank you for bringing this to our attention. We hope that researchers will address this critical knowledge gap and develop the necessary science that can be integrated into future versions of SWAT+.

All the best,

Natalja