# Carbon Storage Units

Good day,

I just ran a carbon storage model and it seems to have worked fine. That being said I just realized that the carbon data I have for my carbon pools is in kg C m−2 . I believe the InVEST manual mentioned that the output of the model is expressed in tons per hectare. I wanted to confirm if there is any conversion into tons per hectare at certain stages of the Carbon Storage InVEST model or if I can assume that my result is expressed in kg C m−2.

This would allow me to know if I can simply continue my analysis by converting the values that I currently have in tons per hectare or if I have to convert the values of my carbon pools into tons per hectare and then run the model for a second time.

Thanks!

The InVEST User Guide specifies that the inputs should be in tons C per hectare, and the spatial results are in tons per pixel. Since the model is converting the input carbon pool values to tons/pixel, it is important to use tons/ha as the input values, otherwise the conversion factor will be incorrect.

~ Stacie

Hi @swolny,

Just a follow-up question: Once we have the spatial results of the output in tons/pixels, what is the process typically used to convert the values to tons/ha?

Thanks,

Jonathan

It’s a simple calculation, based on the area of your pixels relative to one hectare. For example, if your pixels are 30m x 30m, the conversion would be

value in tons/hectare = (value in tons/pixel) * ((30m x 30m) / 10000 m2 per hectare))

~ Stacie

Hello @swolny ,

Thanks for your reply. I used the ArcGIS Pro Zonal Statistics tool which gives me pixel count, area, mean and sum by Land Cover/Land Use. My pixels are 30m x 30m so to convert the area in hectares I divided by 10,000.

I am trying to calculate the sum of carbon storage in tons per hectare for each LULC. Would it make sense to simply divide the ‘SUM’ by my ‘AREA’ (converted in hectares as shown above) to get a value in tons per hectare?

I tried your conversion formula using the ‘MEAN’ as my value in tons/pixel and got much smaller values. I am not sure which of the two methods would provide me with the value I am looking for.

Jonathan

If I’m understanding correctly, I’d think that the sum of carbon storage per hectare would simply be the sum of the 4 carbon pools (from the biophysical table, already given per hectare) for a particular land use/land cover type.

If you want the total carbon stored per LULC class across the whole area the LULC covers, then you’d multiply that by the total area of the LULC. Or, just sum the model output within the LULC, which would give total tons per total area.

~ Stacie

Very clear. Dealing with pixel size and converting to real units can be confusing at times

Thanks!

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