Hello,
The help document says:"We estimate accumulation by multiplying habitat specific rates of carbon accumulation by the given cell area. "So my question is :Where does the model get the cell size?Is it from the projected coordinate system of the TIF map?The raster unit of the map I entered was degrees, not meters.Will it lead to the wrong results?
The second question is :The help document says: "We model accumulation as the rate of carbon retained in the soil in organic form after the first year of decomposition."So what is the “biomass-yearly-accumulation” in the input parameters?Is it increased carbon in plant growth?Does the part of model carbon accumulation include the carbon increase caused by plant growth?
The third question is, All input parameters must be in co2, right?Can we have units of carbon?If I only have the carbon density, can I multiply the carbon density by 3.67 to get the carbon dioxide density?
Looking forward to your reply.Thank you very much.
So this is actually a bug in the User’s Guide, which has been fixed (and thanks for letting us know about it!). As noted in the Outputs section of the User’s Guide chapter, the units are Megatonnes CO2e per hectare.
These units will probably change in a future version of the model to adjust for the area of the pixels.
The biomass-yearly-accumulation field in the input parameters table is the amount of carbon that accumulates in this landcover code in a single year and is discussed in the Carbon Accumulation section of the user’s guide:
We model accumulation as the rate of carbon retained in the soil in organic form after the first year of decomposition. In relation to the annual ecosystem budget, this pool has not been remineralized, so it represents net accumulation. This carbon is usually derived from belowground production, and residence time can range from decades to millennia (Romero et al. 1994, Mateo et al. 1997). This accumulation contributes to the development of carbon “reservoirs” which are considered virtually permanent unless disturbed. Thus, even in the absence of a land-use or land-cover change, carbon continues to be sequestered naturally.
Does that help clarify things?
Yes, input units are in Megatonnes of CO2-equivalent of carbon per hectare per year (see the Inputs section of the user’s guide for details). You’re right that multiplying the carbon density by 3.67 (44/12, based on the molecular weights of C and CO2) should get you the carbon dioxide density for these inputs as far as I can tell 
Let us know if you have any other questions!
James
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