Preprints
https://doi.org/10.5194/bg-2020-476
https://doi.org/10.5194/bg-2020-476

  22 Mar 2021

22 Mar 2021

Review status: this preprint is currently under review for the journal BG.

Methane gas emissions from savanna fires: What analysis of local burning regimes in a working West African landscape tell us

Paul Laris1, Moussa Koné2, Fadiala Dembélé3, Lilian Yang1, and Rebecca Jacobs1 Paul Laris et al.
  • 1Geography Department, California State University Long Beach, 1250 Bellflower Blvd. Long Beach CA 90840, USA
  • 2Institut de Géographie Tropicale (IGT), UFR-SHS, Université FHB de Cocody-Abidjan, Côte d'Ivoire
  • 3Institut Polytechnique Rural de Formation et de Recherche Appliquée de Katibougou, Mali

Abstract. Savanna fires contribute significantly to greenhouse gas emissions. While it is recognized that these fires play an important role in the global methane cycle, there are too few accurate estimates of emissions from West Africa, the continent's most active fire region. Most estimates of methane emissions contain high levels of uncertainty because they are based on generalizations of diverse landscapes that are burned by complex fire regimes. To improve estimates we used an approach grounded in the burning practices of people who set fires to working landscapes. We conducted 97 experimental fires collecting data for savanna type, grass type, biomass composition and amount consumed, scorch height, speed of fire front, fire type and ambient air conditions for two sites in Mali. We collected smoke samples for 36 fires using a canister method. We report values for fire intensity, combustion completeness, patchiness, modified combustion efficiency (MCE) and emission factor (EF). Our study finds that methane EFs ranged from 3.71 g/kg in the early dry season (EDS) to 2.86 in the mid-dry season (MDS). We found head fires had nearly double the CH4 EF of backfires (4.89 g/kg to 2.92). Fires during the MDS have the lowest intensity values and the lowest methane emissions 0.981 g/m2 compared with 1.030 g/m2 for EDS and 1.102 g/m2 for the late dry season (LDS). We conclude that policies aimed at shifting the burning regime earlier to reduce methane emissions will not have the desired effects, especially if fire type is not considered. We recommend using the adjusted mean value of 0.862 g/m2—based on the carbon content for West African grasses—for calculating emissions for West African savannas.

Paul Laris et al.

Status: open (until 15 May 2021)

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Paul Laris et al.

Paul Laris et al.

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Short summary
Savanna fires release methane, a greenhouse gas. Fires play a key role in the global cycle, but there are few studies from West Africa. We conducted 97 experimental fires and collected smoke samples from 36 to determine what affects methane emissions. We found that fires early in the dry season had 30 % higher methane emission factors than those set later, while head-fires had nearly double that of backfires. We conclude that fires set in the mid-season had lowest fire intensity and emissions.
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