What is the unit for InVEST output data?

Hi, InVEST community! I am using the coastal blue carbon model, and I am having difficulty interpreting the results. The user guide said carbon sequestration values are delivered in “Mt CO2e / hectare”, but this makes our numbers extremely large when we multiply the result by the size of the area. Alternatively, it becomes more reasonable when we multiply the result by the number of pixels. So are InVEST output data in “Mt CO2e / hectare” or “Mt CO2e / pixel”? (The input data are all in Mt CO2e / hectare)

InVEST-natcap.invest.coastal_blue_carbon.coastal_blue_carbon-log-2023-08-02–17_02_12.txt (136.1 KB)

Thanks a lot!

@Yirui ,
As the documentation says, the results are in megatonnes of CO2e per hectare.

The model works on each pixel individually, so if you are unsure you can spot-check the results on individual pixels. Do you have a specific example of the math not working out correctly?

Thank you for the prompt reply! The result looks fine, and I am only wondering because the reported carbon sequestration value is 5-6 times that by other researchers for the same area, and more surprisingly, the NPV is 100-1000 times higher. The resulting files are attached below:

total-net-carbon-sequestration.tif (156.0 KB)
net-present-value-at-2060.tif (110.9 KB)

Might there be an issue with my data processing method? I am processing it in ArcGIS by aligning the raster file with a shapefile of the same area and calculating the mean Mt CO2e/ha using the Zonal Statistics as Table command.

Hi @Yirui -

What are the sources for your input carbon pool and accumulation values? And are you sure that they all have units of Mt CO2e/ha? If the output values are very high, it could be because the input values are very high, or have differing units.

Also, what exactly are you comparing with other researchers’ data? Is it the mean value for a particular land cover type? Or a mean value across an area that has a mixture of land cover types? If the latter, I’m not sure how that works, since each land cover type is likely to have very different carbon values. But I don’t know what your area of interest/land cover map looks like.

~ Stacie

Dear Sir,

I have recently started using this Invest model for a Blue carbon project.
I also have similar doubts about the unit of both the input and output values for carbon stocks.

All our input values ( for different carbon pools) used in published literature are in Mg C/ha which is equivalent to Metric tonnes C/ha. Do we need to use these units for the input parameters or do we need to convert them into Mega tonnes CO2 e/ha?

Additionally, the Global mean carbon accumulation rate (CAR) is estimated to be 233 ± 280 g C m−2 yr−1 which is equivalent to ~8.5x10-6 Mega tonnes CO2e/ha (~0.0000085). This value looks very less. (Redirecting).
Please correct me if I am wrong and guide me in this matter.
Thank you.

Welcome to the forum @Dipnarayan -

The User Guide says this about units:

Although this user’s guide chapter refers to units in Megatonnes of CO2-equivalent per hectare, the model does no conversion of units whatsoever, and so any units representing the habitat-specific rate of accumulation or emissions, so long as they are consistent across all model inputs, may be used.

Assuming that this is correct, and the model actually doesn’t do any conversion of units, then your results should have the same units as the data you provided as input. So if you’re giving all of your input values in Mg C/ha, then the results should also be in Mg C/ha.

If you think there’s a problem with how the model is working, I’ll ask someone on the software team to take a look at the code to verify that it is not changing units.

~ Stacie

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