the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Jul 2025
Radiative forcing due to shifting southern African fire regimes
Abstract. Landscape fires emit climate-influencing greenhouse gases and aerosols. The vast majority of landscape fire emissions originate from tropical savannas, especially in Africa. During the fire season, the climatic and fuel conditions change, and fires burning later in the dry season consume drier vegetation and occur in drier weather conditions than earlier fires. Previous studies have shown that it is possible to reduce emissions of some greenhouse gases (CH4 and N2O) by using ‘prescribed’ fires, i.e. deliberate burning in the early dry season. In this study we examine the climate effect of (deliberately) changing fire regimes beyond CH4 and N2O, including aerosols and other short-lived species, CO2, and changes to surface albedo. We find that in general shifting burning earlier in a single fire season results in global negative climate forcing (cooling) of around –0.001 to –0.002 Wm−2 (long-term) or –0.006 (short-term) Wm−2, compared to less than -0.0005 Wm−2 if only considering CH4 and N2O. CO2 emissions reduction through emission factor changes and burned area reduction is the largest contributing factor, though especially in the short term albedo effects are also substantial. Shifting fire activity towards the late fire season generally produces a positive climate forcing (warming) of a smaller magnitude. We find too that some localities within our study area have a potentially disproportionately large impact on our results, such that the efficacy of any fire regime change with respect to climate forcing must be carefully considered on a local scale.
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CC1: 'Comment on egusphere-2025-3394', Oliver Perkins, 01 Aug 2025
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Thank you to the authors for this interesting paper. I am basically supportive of what you are doing here. I appreciate that your main focus is atmospheric chemistry, and there you produce some very interesting results. However, I have some clarifying questions about the human dimensions of your scenarios. I think their presentation should be tweaked to guard against potential misuse, e.g., in support of unsuitable savanna abatement schemes.
(1) Human impact on the baseline scenario
I think you need to do more to recognise that in your study region, human controlled burning already plays a significant role in the fire regime. It is good you recognise that EDS burning is present in many parts of the study region. However, it is not always as simple as human EDS burning vs LDS wildfires.
For example, in North-eastern Zambia, which has a significant impact on your results, there is widespread fire use for shifting cultivation1,2,3. This often occurs very late in the dry season, just before the first rains. This then, is a very different form of fire use from early dry-season burning: it either occurs before the first rains, or it doesn't make sense from an agricultural point of view. Hence, it is not that surprising that pushing this into the early dry season has a substantial impact on RF, but I'm not sure of the real world applicability of this finding.
(2) Human implications of shifting fire use
I think this difficulty may arise from an overreliance on the Australian case study as a conceptual model. There, Aboriginal fire was systematically removed from the landscape, before its targeted reintroduction. As such, a targeted early burn was possible. This is not the case in your study region, where fire use is a fundamental component of peoples' livelihoods, and often their social/religious identities, and occurs at many points throughout the dry season for different reasons. Hence, intervening in the way implied by your scenarios is likely to be much more complicated than in the Australian case [see 4 for a real world example of what happens when this goes wrong].
It is good that you note the possibility of local/regional scale difficulties in implementing your scenarios. However, the section beginning at line 674 should be rewritten to reflect the different context in which your scenarios are being run to Northern Australia, and do more to highlight they are theoretical maximums that would have very substantial feasibility challenges for real world application. Some more engagement with the specifics of the study context would be useful. See 5 for a global synthesis / index of literature on human fire use, from where I located refs 1,2,3.Thank you again for the interesting work.
Oliver Perkins
1 https://repository.kulib.kyoto-u.ac.jp/items/02ea39b5-5ea9-4571-a37c-12afc3ca5f0b
2 https://www.tandfonline.com/doi/full/10.1080/00380768.2014.883487
3 https://www.jstor.org/stable/30135835#metadata_info_tab_contents4 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023EF003552
5 https://figshare.com/collections/DAFI_a_global_database_of_Anthropogenic_Fire/5290792/4Citation: https://doi.org/10.5194/egusphere-2025-3394-CC1 -
RC1: 'Comment on egusphere-2025-3394', Anonymous Referee #1, 09 Sep 2025
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Eames et al. present a comprehensive and well-structured analysis of the climate impacts associated with deliberate modifications to fire regimes in Southern Africa. The study extends beyond the roles of CH₄ and N₂O to also account for aerosols, other short-lived species, CO₂, and surface albedo changes. A range of burning scenarios is investigated, and their corresponding radiative forcings are assessed using WRF-Chem model simulations. The model outputs are further evaluated against both ground-based observations and satellite datasets. Overall, the results are clearly presented, and the work fits well within the scope of ACP. Few comments are as follows:
Major Comments:
- The manuscript is generally quite lengthy, particularly the Methodology section. The authors may consider moving various details (e.g. WRF-Chem model details including Appendix C, selected figures from the Appendix, etc..….) to the supplementary material. This would improve readability, streamline the manuscript, and allow greater emphasis on the Results and Discussion sections.
- The manuscript should be refined in its wording to more explicitly address the real-world implications of shifting burning to the early dry season (EDS), including potential adverse consequences. In addition, the authors should carefully discuss the extent to which the findings from EDS burning in this study may, or may not, be applicable to other fire-prone regions globally. It should also be made clear how and to what extent these results can be referenced, and where caution is required in their broader application.
Minor suggestions:
- Lines 10-11: It will be good to mention quantitative how much warming is produced by shifting burning to late fire season.
- Figure 2: It would be helpful to further clarify Figure 2a, specifically what the y-axis represents and how the different peaks in EDS, LDS, and the mean should be interpreted.
- Figure 6: Since WRF-Chem provides AOD data in regions where MODIS observations are unavailable, it would be useful to show a continuous AOD distribution in Figure 2b.
- Figure 7: For panel (a): Since MODIS data are available only once per day, is the WRF-Chem data averaged over the same daily period near the MODIS overpass time? Additionally, in areas where MODIS data are unavailable, as shown in Figure 6, are these regions excluded from the WRF-Chem averaging? For panel (b): Is the WRF-Chem averaging performed across the AERONET sites? What temporal resolution of AERONET AOD data is used here, and is the WRF-Chem averaging done at the same temporal resolution?
Citation: https://doi.org/10.5194/egusphere-2025-3394-RC1
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