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

Abstract

Abstract. Savanna fires contribute significantly to greenhouse gas emissions. While it is recognized that these fires play a critical 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 as 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 collected and analyzed smoke samples for 36 experimental fires using a canister method for the early dry season (EDS) and mid-dry season (MDS). We also collected 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 report values for fire intensity, combustion completeness, patchiness, modified combustion efficiency (MCE), emission factor (EF) and methane emission density. Our study found that mean methane EFs ranged from 3.83 g kg−1 in the EDS to 3.18 g kg−1 in the MDS, but the small sample did not provide enough power for this effect to be significant. We found head fires had nearly double the CH4 EF of backfires (5.12 g kg−1 to 2.74), a significant difference. Byram's fire intensity was a significant driver of CH4 EF but with weak effect. Methane emission density increased marginally from 0.839 g m−2 in the EDS to 0.875 g m−2 in the MDS, a difference that was not significant. Head fires, however, had much higher emission densities than backfires – 1.203 vs. 0.708 g m−2 – respectively, a significant difference. We suggest the reason for the higher methane emissions from head fires, which have higher intensity, is the longer flame lengths that burn green leaves on trees, releasing methane. 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. Future research should consider the state and amount of leafy biomass combusted in savanna fires.

A multicriteria approach for biomass availability assessment and selection for energy production in Burkina Faso: A hybrid AHP-TOPSIS approach

“…In the present study, the evaluation is done on one biomass unit to maintain the criteria's independence. The EF considered is 3.3 g/kg for methane [ 67 ] and 0.07 g/kg for N 2 O [ 63 ].…”

The role of people, parks and precipitation on the frequency and timing of fires in a sub-Saharan savanna ecosystem

“…Building on our findings concerning fire regimes and their underlying drivers, it is essential to place our research within the broader context of mitigating methane emissions from savanna wildfires, a globally recognised challenge linked to reducing methane, a potent greenhouse gas, with increasing concerns about wildfires as a significant contributor (Lipsett-Moore et al 2018;Laris et al 2021Laris et al , 2023. Although earlier research had suggested the potential for substantial emission reductions through a global-scale strategy of shifting fire periods to the early dry season in African savannas (Lipsett-Moore et al 2018), our findings challenge this assumption.…”

“…This observation underscores that mere adjustments to the timing of fire regimes may prove inadequate for achieving substantial emissions reductions, given that many communities across sub-Saharan Africa are already initiating fires early in the dry season. Furthermore, as others have noted, the complex nature of wildfire emissions from fires raises doubts about whether altering the timing of burning would yield the desired outcomes (Laris et al 2021(Laris et al , 2023.…”

Assessing Carbon Emissions from Biomass Burning in Croplands in Burkina Faso, West Africa

“…In our case, biomass was obtained from field preparation, i.e., the burning of cleared biomass before the cropping, whereas most studies focused on the burning of residues produced after the harvest. Laris et al [58] showed that leaf fall is another factor influencing emission factors. Some studies reported a high variability of CO and CH 4 EFs, which can be attributed to spatial variability, vegetation type and burning time [57,59].…”