Wetland methane emissions

[James King]

Hi all,

We're using CLM5 (in CESM2.2.0) in both SP and BGC-CROP modes and we're interested in calculating the methane emissions from wetlands. Is there a way we can scale grid-cell surface CH4 flux to the atmosphere to give a wetland CH4 flux? We tried scaling by land fraction and wetland fraction but got a total of about 50Tg/yr which seems low (ballpark figure we've seen in the literature is ~150Tg/yr). Is there another scaling factor we are missing, or is our approach the wrong one?

Many thanks,

James

 

[oleson]

Well, we don't represent wetlands explicitly in CLM5, so are you using a separate wetland fraction dataset perhaps?
That said, I thought we had a reasonable global net CH4 emissions (~270 Tg CH4 per year) at some point:

BG - Barriers to predicting changes in global terrestrial methane fluxes: analyses using CLM4Me, a methane biogeochemistry model integrated in CESM

bg.copernicus.org

 

[James King]

Hi Keith,

Yep, we saw that paper - we're just not sure how that figure was arrived at based on the output fields we have in CLM5.

Thanks,

James

 

[oleson]

I think the global estimate is arrived at by doing a global sum of FCH4 using grid cell area and land fraction?

 

[James King]

We also scaled by FINUNDATED, interpreting this as wetland fraction. Is this step unneccesary?

Thanks,

James

 

[oleson]

My understanding is that the global estimate in Riley's paper represents emission from both inundated and non-inundated fractions plus lakes as well I think.
I'm not sure whether scaling by FINUNDATED is appropriate for estimating emissions from wetlands. I will ping a couple of people here who might know more about this. You could also contact Bill Riley.

 

[James King]

Thanks Keith!