How to correct the yield results in the model?

[Tonyzhao610]

I've noticed that "fertproductchange" (changes in yield due to fertilization) and "irrproductchange" (changes in yield due to irrigation) seem to be key factors in altering yield outcomes. Now, I have simulation results for yield in a particular region, and I'm wondering how to adjust the yield in the GCAM model while keeping the cultivated area constant. Additionally, I hope that the changes in yield can trigger corresponding changes in related factors (such as agricultural water usage, energy consumption during fertilization, agricultural carbon emissions, etc.). Thanks！

[pkyle]

In the representation in the model, all three of these inputs (fertilizer, water, land) are exogenous. Fertilizer and water are indicated per unit of crop output (kg N / kg crop, m3 water / kg crop). The land input is indicated as an exogenous yield in the base year (production / land area), increased in future years with the AgProdChange parameter. It really is up to the model user to ensure consistency between these three variables; there is no formal interrelationship between them in the model code. As a simple example, you could assign AgProdChange to return a very high yield while simultaneously taking the N fertilizer input down towards zero, and the model wouldn’t know that such a combination is not biophysically possible.
However the land allocation is endogenous; model users have only limited ability to assign land allocation. So the scenario that you are describing, where the land allocation is exogenously specified, while the relationship between the three inputs to production is endogenous, is not something that GCAM is well suited to perform.