Clarify Expected Deforestation Adjustment

[agcopenhaver]

Hi Folks -

I get a lot of questions on how to handle the "expected deforestation" bit of the tool.

Users seem to be unclear on what value to provide there and how it corresponds with the BVP length - especially as the HRP and BVP are different lengths.

I'm just curious if we think, given that the output of the tool is meant to be an annualized map with estimated def in ha/yr as the unit, we might just ask for the expected deforestation rate per year and remove the "Length of the VP in years"

I'd be happy to submit a PR for this, but before I do, I want to make sure we're aligned on it.

-Andrew

[YaoTingYao]

Hi @agcopenhaver, the enhancement sounds great to me—please feel free to submit the PR. Most folks in CGA are off this week, so I'll share this with them next week. Cheers!

[YaoTingYao]

Hi @agcopenhaver, while testing the new calculation— using expected deforestation rate per year and remove the "Length of the VP in years"—we noticed an important point that requires consideration.

In the original calculation, we computed:
AR = expected_deforestation / MD and then checked if AR > 1.00001 then recalculating AR if needed.

Since we are now using the expected annual deforestation rate, the AR calculation must be adjusted to remain consistent with the original approach. There are two potential mathematic approaches, but both approaches still require the user’s input for the time to ensure the calculation is accurate.

Approach 1:

AR = expected_deforestation_annual / MD_annual

where MD_annual is MD divided by the time factor (6). Then, check if AR > 1.00001.

Approach 2:

AR = expected_deforestation_annual / MD

and then check if AR > 0.166668 (which is equivalent to 1.00001 divided by 6).

After further discussion with Verra, we decided to retain the original calculation method but adjust the expected deforestation to an annual rate. This aligns with Verra’s workflow, which now provides annual figures in practice, and helps prevent user confusion. In this revision behind the scene, the result are identical with the original calculation as setting the 'Length of the VP in years' to 1, dividing the expected value by 1 to yield the annualized expected deforestation rate.