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Roughly half of global fire emissions originate from savannas, and emission factors (EF) are used to quantify the amount of trace gases and aerosols emitted per unit dry matter burned. It is well known that these EFs vary substantially even within a single biome but so far quantifying their dynamics has been hampered by a lack of EF measurements. Therefore, global emission inventories currently use a static averaged EF for the entire savanna biome. To increase the spatiotemporal coverage of EF measurements, we collected over 4500 EF bag measurements of CO2, CO, CH4 and N2O using an unmanned aerial system (UAS) and measured fuel parameters and fire severity proxies during 129 individual landscape fires. These measurements spanned various widespread savanna ecosystems in Africa, South America and Australia, with early and late dry season campaigns. We trained random forest (RF) regressors to estimate daily dynamic EFs for CO2, CO, CH4 and N2O at 500×500-meter resolution based on satellite and reanalysis data. The RF models reduced the difference between measured and modelled EFs by 60-85% compared to static biome averages. The introduction of EF dynamics resulted in a spatial redistribution of CO, CH4 and N2O emissions compared to the Global Fire Emissions Database version 4 (GFED4s) with higher emissions in higher rainfall savanna regions. While the impact from using dynamic EFs on the global annual emission estimates from savannas was relatively modest (+2% CO, -5% CH4 and -18% N2O), the impact on local EFs may exceed 60% under dry seasonal conditions.

Landscape fires, predominantly in the frequently burning global savannas, are a substantial source of greenhouse gases and aerosols. The impact of these fires on atmospheric composition is partially determined by the chemical breakup of the elements in the fuel into individual emitted chemical species, which is described by emission factors (EFs). These EFs are known to be dependent on, amongst others, the type of fuel consumed, the moisture content of that fuel and the meteorological conditions during the fire, indicating that savanna EFs are temporally and spatially dynamic. Global emission inventories, however, rely on static biome-averaged EFs which makes them ill-suited for the estimation of regional biomass burning (BB) emissions and for capturing the effects of shifts in fire regimes. In this study we explore the main drivers of EF-variability within the savanna biome and assess which geospatial proxies can be used to estimate dynamic EFs for global models. We collected over 4500 EF bag measurements of CO2, CO, CH4 and N2O using an unmanned aerial system (UAS), and measured fuel parameters and fire severity proxies during 129 individual fires. The measurements cover a variety of savanna ecosystems under different seasonal conditions, sampled over the course of six fire seasons between 2017 and 2022. We complemented our own data with EFs from 85 fires with known locations and dates listed in the literature. Based on the locations, dates and time of the fires we retrieved a variety of fuel-, weather- and fire severity proxies (i.e. possible predictors) using globally available satellite and reanalysis data. We then trained random forest (RF) regressors to estimate dynamic EFs for CO2, CO, CH4 and N2O and calculated the spatiotemporal impact on BB emissions over the 2002–2016 period using the Global Fire Emissions Database version 4 with small fires (GFED4s). We found that the most important field indicators for the EFs of CO2, CO and CH4 were tree cover density, fuel moisture content and the grass to litter ratio. The grass to litter ratio and the nitrogen to carbon ratio were important indicators for N2O EFs. RF models using satellite observations performed well for the prediction of EF variability in the measured fires with out-of-sample correlation coefficients between 0.80 and 0.99, reducing the error in EF estimates by 60–85 % compared to static biome averages. Using dynamic EFs, global savanna emission estimates for 2002–2016 were 1.8 % higher for CO while CH4 and N2O emissions were respectively 5 % and 18 % lower compared to GFED4s. On a regional scale we found a spatial redistribution compared to GFED4s with higher CO, CH4 and N2O EFs in mesic regions and lower ones in xeric regions. Seasonal drying resulted in a decrease of the EFs of these species with the fire season progressing, with a stronger trend in open savannas than woodlands. Contrary to the minor impact on annual savanna average emissions, the model predicts localized reductions in EFs of CO, CH4 and N2O exceeding 60 % under seasonal conditions.

Land occupation and management systems have defined fire regimes and landscapes for millennia. The savanna biome is responsible for 86% of all fire events, contributes to 10% of the total carbon emissions annually and is home to 10% of the human population. European colonization has been associated with the implementation of fire suppression policies in many tropical savanna regions, markedly disrupting traditional fire management practices and transforming ecosystems. In this paper we assess savanna burning approaches from pre-colonial to contemporary eras in three regions: northern Australia, southern Africa and Brazil. In these regions, fire suppression policies have led to (i) conflicts between government authorities and local communities; (ii) frequent late dry season wildfires and/or (iii) woody encroachment. Such consequences are facilitating changes to fire management policies, including recognition and incorporation of traditional ecological knowledge in contemporary community-based adaptive savanna fire management. Such programs include implementation of prescribed early dry season fires and, in some regions, generating income opportunities for rural and traditional communities through the reduction of late dry season wildfires and associated greenhouse gas emissions. We present a brief history of fire management policies in these three important savanna regions, and identify ongoing challenges for implementation of culturally and ecologically sustainable fire management policies.

Savanna fires occurring in sub-Saharan Africa account for over 60% of global fire extent, of which more than half occurs in the Southern Hemisphere contributing ~29% of global fire emissions. Building on experience in reducing savanna fire emissions in fire-prone north Australian savannas through implementation of an internationally accredited ‘savanna burning’ emissions abatement methodology, we explore opportunities and challenges associated with the application of a similar approach to incentivise emissions reduction in fire-prone southern African savannas. We first show that for a focal region covering seven contiguous countries, at least 80% of annual savanna large fire (>250 ha) extent and emissions occur under relatively severe late dry season (LDS) fire-weather conditions, predominantly in sparsely inhabited areas. We then assess the feasibility of adapting the Australian emissions abatement methodology through exploratory field studies at the Tsodilo Hills World Heritage site in north-west Botswana, and the Niassa Special Reserve in northern Mozambique. Our assessment demonstrates that application of a savanna burning emissions abatement method focused on the undertaking of strategically located early dry season (EDS) burning to reduce LDS wildfire extent and resultant emissions meets key technical criteria, including: LDS fine fuels tend to be markedly greater than EDS fuels given seasonal leaf litter inputs; LDS fires tend to be significantly more severe and combust more fuels; methane and nitrous oxide emission factors are essentially equivalent in EDS and LDS periods under cured fuel conditions. In discussion we consider associated key implementation challenges and caveats that need to be addressed for progressing development of savanna burning methods that incentivise sustainable fire management, reduce emissions, and support community livelihoods in wildfire-dominated southern African savannas.

Savannas constitute the most fire-prone vegetation type on earth and are a significant source of greenhouse gas emissions. Most savanna fires are lit by people for a variety of livelihood applications. 'Savanna burning' is an accountable activity under the Kyoto Protocol, but only Australia, as a developed economy, accounts for emissions from