Accounting for peat fires in the Fire INventory from NCAR (FINN): Improved air pollutant emissions estimates for tropical peatlands using soil moisture, drainage density and fire history.

The Fire INventory from NCAR (FINN) is a daily, high resolution (1 km) fire emissions inventory designed for use in atmospheric chemistry models. FINN uses a ‘bottom-up’ approach to estimate fire emissions. Satellite observations of active fires from MODIS (and VIIRS) are combined with land cover, emission factors and fuel loadings to predict fire emissions of key air pollutants. However, one of the key limitations of FINN is lack of peat fire emissions in the dataset, which only accounts above ground vegetation fires. Therefore, neglecting an important emissions source given the extensive abundance of peat in key tropical regions. Fires that occur on the surface of peatland can burn into the below-ground organic layers (up to 0.6 m). Peat fires can smoulder for weeks after the surface fire has extinguished, resulting in substantially greater emissions compared to surface vegetation fires. Therefore, it is essential to include peat fires in FINN.

Globally, peatlands cover >4 million km² (3 %) of the global land area. However, emissions from the combustion of tropical and Arctic-boreal peat alone account for a disproportionately large fraction of total global carbon emissions (13 %). This is driven by above ground fires burning into the carbon rich peat below.

We first focus on tropical peatlands in Indonesia since these have well documented impacts on air quality. Indonesia is home to a large proportion (36 %) of total tropical peatlands, and a large fraction of fires in Indonesia occur on peatlands. For example, in 2015 53 % of fires in Indonesia occurred on peatland, accounting for only 12 % of the land area. Peat fires contributed 71-95 % of the particulate matter (PM_2.5) fire emissions, though emissions are uncertain.

Our work builds upon previous work, which estimated Indonesian peat fire emissions for FINN.  Previously, satellite-derived soil moisture was used to determine a straightforward linear relationship with burn depth of fires that occurred on peatlands. We further develop this method adding additional complexity by using ground-based measurements of burn depth collocated with satellite soil moisture. We also consider canal density and fire frequency maps to account for changes in burn depth with drainage and fire history.

We plan to apply this method to other tropical peatland and boreal regions, so we welcome any discussions on our current work so far and/or future plans.