Biomass burning emissions
Biomass burning emissions data from the Global Fire Data (GFED version 3;
http://www.globalfiredata.org/Data/index.html) are used. Monthly CO2 emissions fields at
0.5°x0.5° degree resolution and over 1997-2010 period are considered. Figure 1 illustrates the
mean annual fire emission over the globe from this GFED release.
Figure 1: Annual carbon emissions (as g C m-2 year-1), averaged over 1997-2010 from GFED database
(http://www.globalfiredata.org/Data/index.html)
1) Biomass burning emissions in the CCDAS
The GFED data are breakdown into 6 sectors: deforestation, peat fires, savanna fires, agriculture,
forest fires, and woodland. With these data, we generated fluxes of CO2 emissions relevant for
typical “burning – regrowth” processes as detailed hereafter. These fluxes are then prescribed to the
CCDAS over the period of 1989-2009. Before 1997, we use for each year, the mean annual field
derived from the fluxes over the 1997-2010 period. In order to account for fundamental
differences between the six initial categories, we grouped the GFED emissions in 3 types and
made specific treatments for each of this type:

Emissions from deforestation and peat fires
These emissions are considered to be permanent carbon lost to the atmosphere, at least
over the considered time scales. We have rescaled these fluxes to 1.1 GtC/yr globally and at
annual scale to cope with values reported in the literature for deforestation (Houghton R.
2003).

Emissions from agriculture and savanna fires
These emissions are compensated by a sink during the regrowth of these biomes (i.e.,
savanna and the type of plant on the farmland). Indeed, these effects are not completely
accounted in ORCHIDEE as the model does not simulate savanna and agriculture fire. Hence,
the emissions over the whole period and for each pixel are zero, but we have their seasonal
variations.

Emissions from woodland and burnt forests
We considered that at steady state and for a given region there are forests/woodland that
burn and in the same time nearby forests/woodland that are re-growing. This is because the
ORCHIDEE model does not account for this regrowth. The strong assumption is that over
century time scale the forest/woodland system is at steady state over a given regions (few
thousand km size), i.e. there is no net deforestation. We selected an ensemble of small
regions over which we calculated the regrowth of these biomes. The derived emissions over
the whole period and for each region are zero, we have their spatial and temporal
variations.
The overall biomass burning flux considered in the CCDAS for the optimization process is the
sum of the three fluxes as described above.
2) Uncertainties in biomass burning emissions
The uncertainties in the derived biomass burning fluxes were difficult to assess. The GFED data
do not provide uncertainties in the emissions. However, uncertainties in the burnt areas are
given. We are currently working on the possibility to use this information and to derive an
uncertainty on the biomass burning fluxes to be used in the final CCDAS version (i.e. with the
optimization of the biomass emission for several regions).
3) Availability
The biomass burning data are freely available under:
http://www.globalfiredata.org/
4) References
Houghton, R. A. (2003) Revised estimates of the annual net flux of carbon to the atmosphere from
changes in land use and land management 1850-2000. Tellus 55B: 378-390.