### 2.24.1.3. Fire impact[¶](#fire-impact "Permalink to this headline")

In post-fire regions, we calculate PFT-level fire carbon emissions from biomass burning of the \\(j\\)th PFT, \\({\\phi}\_{j}\\) (g C s\-1), as

(2.24.26)[¶](#equation-23-26 "Permalink to this equation")\\\[\\phi \_{j} =A\_{b,j} \\mathbf{C}\_{j} \\bullet \\mathbf{CC}\_{j}\\\]

where \\(A\_{b,j}\\) (km2 s\-1) is burned area for the \\(j\\)th PFT; **C**j =(\\(C\_{leaf}\\), \\(C\_{stem}\\), \\(C\_{root}\\), \\(C\_{ts}\\)) is a vector with carbon density (g C km \-2) for leaf, stem (live and dead stem), root (fine, live coarse and dead coarse root), and transfer and storage carbon pools as elements; \\(\\mathbf{CC}\_{j}\\) = (\\(\\mathbf{CC}\_{leaf}\\), \\(\\mathbf{CC}\_{stem}\\), \\(\\mathbf{CC}\_{root}\\), \\(\\mathbf{CC}\_{ts}\\)) is the corresponding combustion completeness factor vector ([Table 2.24.1](#table-pft-specific-combustion-completeness-and-fire-mortality-factors)). Moreover, we assume that 50% and 28% of column-level litter and coarse woody debris are burned and the corresponding carbon is transferred to atmosphere.

Tissue mortality due to fire leads to carbon transfers in two ways. First, carbon from uncombusted leaf, live stem, dead stem, root, and transfer and storage pools \\(\\mathbf{C^{'} \_{j1}} ={(C\_{{leaf}} (1-CC\_{{leaf}} ),C\_{{livestem}} (1-CC\_{{stem}} ),C\_{{deadstem}} (1-CC\_{{stem}} ),C\_{{root}} (1-CC\_{{root}} ),C\_{{ts}} (1-CC\_{{ts}} ))}\_{j}\\) (g C km\-2) is transferred to litter as

(2.24.27)[¶](#equation-23-27 "Permalink to this equation")\\\[\\Psi \_{j1} =\\frac{A\_{b,j} }{f\_{j} A\_{g} } \\mathbf{C^{'} \_{j1}} \\bullet M\_{j1}\\\]

where \\(M\_{j1} =(M\_{{leaf}},M\_{{livestem,1}},M\_{{deadstem}},M\_{{root}},M\_{{ts}} )\_{j}\\) is the corresponding mortality factor vector ([Table 2.24.1](#table-pft-specific-combustion-completeness-and-fire-mortality-factors)). Second, carbon from uncombusted live stems is transferred to dead stems as:

(2.24.28)[¶](#equation-23-28 "Permalink to this equation")\\\[\\Psi \_{j2} =\\frac{A\_{b,j} }{f\_{j} A\_{g} } C\_{livestem} (1-CC\_{stem} )M\_{livestem,2}\\\]

where \\(M\_{livestem,2}\\) is the corresponding mortality factor ([Table 2.24.1](#table-pft-specific-combustion-completeness-and-fire-mortality-factors)).

Fire nitrogen emissions and nitrogen transfers due to fire-induced mortality are calculated the same way as for carbon, using the same values for combustion completeness and mortality factors. With CLM’s dynamic vegetation option enabled, the number of tree PFT individuals killed by fire per km2 (individual km\-2 s\-1) is given by

(2.24.29)[¶](#equation-23-29 "Permalink to this equation")\\\[P\_{disturb,j} =\\frac{A\_{b,j} }{f\_{j} A\_{g} } P\_{j} \\xi \_{j}\\\]

where \\(P\_{j}\\) (individual km\-2) is the population density for the \\(j\\) th tree PFT and \\(\\xi \_{j}\\) is the whole-plant mortality factor ([Table 2.24.1](#table-pft-specific-combustion-completeness-and-fire-mortality-factors)).

