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Open accessJournal ArticleDOI: 10.1073/PNAS.2011160118

African burned area and fire carbon emissions are strongly impacted by small fires undetected by coarse resolution satellite data.

02 Mar 2021-Proceedings of the National Academy of Sciences of the United States of America (National Academy of Sciences)-Vol. 118, Iss: 9, pp 1-7
Abstract: Fires are a major contributor to atmospheric budgets of greenhouse gases and aerosols, affect soils and vegetation properties, and are a key driver of land use change. Since the 1990s, global burned area (BA) estimates based on satellite observations have provided critical insights into patterns and trends of fire occurrence. However, these global BA products are based on coarse spatial-resolution sensors, which are unsuitable for detecting small fires that burn only a fraction of a satellite pixel. We estimated the relevance of those small fires by comparing a BA product generated from Sentinel-2 MSI (Multispectral Instrument) images (20-m spatial resolution) with a widely used global BA product based on Moderate Resolution Imaging Spectroradiometer (MODIS) images (500 m) focusing on sub-Saharan Africa. For the year 2016, we detected 80% more BA with Sentinel-2 images than with the MODIS product. This difference was predominately related to small fires: we observed that 2.02 Mkm2 (out of a total of 4.89 Mkm2) was burned by fires smaller than 100 ha, whereas the MODIS product only detected 0.13 million km2 BA in that fire-size class. This increase in BA subsequently resulted in increased estimates of fire emissions; we computed 31 to 101% more fire carbon emissions than current estimates based on MODIS products. We conclude that small fires are a critical driver of BA in sub-Saharan Africa and that including those small fires in emission estimates raises the contribution of biomass burning to global burdens of (greenhouse) gases and aerosols.

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Open accessJournal ArticleDOI: 10.1111/GCB.15591
Abstract: Fires, among other forms of natural and anthropogenic disturbance, play a central role in regulating the location, composition and biomass of forests. Understanding the role of fire in global forest loss is crucial in constraining land-use change emissions and the global carbon cycle. We analysed the relationship between forest loss and fire at 500 m resolution based on satellite-derived data for the 2003-2018 period. Satellite fire data included burned area and active fire detections, to best account for large and small fires, respectively. We found that, on average, 38 ± 9% (± range) of global forest loss was associated with fire, and this fraction remained relatively stable throughout the study period. However, the fraction of fire-related forest loss varied substantially on a regional basis, and showed statistically significant trends in key tropical forest areas. Decreases in the fraction of fire-related forest loss were found where deforestation peaked early in our study period, including the Amazon and Indonesia while increases were found for tropical forests in Africa. The inclusion of active fire detections accounted for 41%, on average, of the total fire-related forest loss, with larger contributions in small clearings in interior tropical forests and human-dominated landscapes. Comparison to higher-resolution fire data with resolutions of 375 and 20 m indicated that commission errors due to coarse resolution fire data largely balanced out omission errors due to missed small fire detections for regional to continental-scale estimates of fire-related forest loss. Besides an improved understanding of forest dynamics, these findings may help to refine and separate fire-related and non-fire-related land-use change emissions in forested ecosystems.

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Topics: Forest dynamics (62%), Deforestation (56%), Disturbance (ecology) (50%)

6 Citations


Journal ArticleDOI: 10.1029/2021JD034984
Abstract: Biomass burning (BB) produces large quantities of carbonaceous aerosol (black carbon and organic aerosol, BC and OA, respectively), which significantly degrade air quality and impact climate. BC absorbs radiation, warming the atmosphere, while OA typically scatters radiation, leading to cooling. However, some OA, termed brown carbon (BrC), also absorbs visible and near UV radiation; although, its properties are not well constrained. We explore three aircraft campaigns from important BB regions with different dominant fuel and fire types (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen [WE-CAN] in the western United States and ObseRvations of Aerosols above CLouds and their intEractionS and Cloud-Aerosol-Radiation Interactions and Forcing for Year downwind of southern Africa) and compare them with simulations from the global chemical transport model, GEOSChem using GFED4s. The model generally captures the observed vertical profiles of carbonaceous BB aerosol concentrations; however, we find that BB BC emissions are underestimated in southern Africa. Our comparisons suggest that BC and/or BrC absorption is substantially higher downwind of Africa than in the western United States and, while the Saleh et al. (2014, https://doi.org/10.1038/ngeo2220) and FIREX parameterizations based on the BC:OA ratio improve model-observation agreement in some regions, they do not sufficiently differentiate absorption characteristics at short wavelengths. We find that photochemical whitening substantially decreases the burden and direct radiative effect of BrC (annual mean of +0.29 W m without whitening and +0.08 W m with). Our comparisons suggest that whitening is required to explain WE-CAN observations; however, the importance of whitening for African fires cannot be confirmed. Qualitative comparisons with the OMI UV aerosol index suggest our standard BrC whitening scheme may be too fast over Africa. Plain Language Summary Smoke from fires has large air quality, health, and climate impacts. However, both the quantity of smoke and its ability to warm or cool the atmosphere remain poorly understood. The two major particle components of smoke (black carbon [BC] and organic aerosol [OA]) interact with incoming solar radiation in distinct ways, with BC generally absorbing light and leading to warming while OA mainly scatters radiation causing cooling. Some types of OA absorb over specific wavelengths of light; these particles are called brown carbon (BrC). Our work uses observations from the western United States and downwind of southern Africa and a global model to better understand the air quality and climate effects of fires in these regions. We find that BC emissions from fires are CARTER ET AL. © 2021. American Geophysical Union. All Rights Reserved. Investigating Carbonaceous Aerosol and Its Absorption Properties From Fires in the Western United States (WECAN) and Southern Africa (ORACLES and CLARIFY) Therese S. Carter , Colette L. Heald , Christopher D. Cappa , Jesse H. Kroll , Teresa L. Campos , Hugh Coe , Michael I. Cotterell , Nicholas W. Davies, Delphine K. Farmer , Cathyrn Fox, Lauren A. Garofalo , Lu Hu , Justin M. Langridge , Ezra J. T. Levin , Shane M. Murphy , Rudra P. Pokhrel , Yingjie Shen, Kate Szpek , Jonathan W. Taylor , and Huihui Wu Civil and Environmental Engineering Department, Massachusetts Institute of Technology, Cambridge, MA, USA, Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA, Department of Civil and Environmental Engineering, University of California at Davis, Davis, CA, USA, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA, Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA, Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK, School of Chemistry, University of Bristol, Bristol, UK, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK, Met Office, Exeter, UK, Department of Chemistry, Colorado State University, Fort Collins, CO, USA, Department of Chemistry and Biochemistry, University of Montana, Missoula, MT, USA, Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA, Handix Scientific, Boulder, CO, USA, Department of Atmospheric Science, University of Wyoming, Laramie, WY, USA, Now at Department of Physics, North Carolina A&T State University, Greensboro, NC, USA Key Points: • Per model-measurement analysis, black and brown carbon (BrC) absorption efficiencies are higher in smoke from Africa relative to the western United States • Modeling BrC absorption with black carbon:organic aerosol (BC:OA) parameterizations improves modelobservation agreement without sufficiently distinguishing regions • A universal 1-day BrC whitening timescale in the model performs better against observations than a scheme based on OH exposure Supporting Information: Supporting Information may be found in the online version of this article.

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5 Citations


Open accessJournal ArticleDOI: 10.5194/BG-18-4117-2021
12 Jul 2021-Biogeosciences
Abstract: . Environmental science is increasingly reliant on remotely sensed observations of the Earth's surface and atmosphere. Observations from polar-orbiting satellites have long supported investigations on land cover change, ecosystem productivity, hydrology, climate, the impacts of disturbance, and more and are critical for extrapolating (upscaling) ground-based measurements to larger areas. However, the limited temporal frequency at which polar-orbiting satellites observe the Earth limits our understanding of rapidly evolving ecosystem processes, especially in areas with frequent cloud cover. Geostationary satellites have observed the Earth's surface and atmosphere at high temporal frequency for decades, and their imagers now have spectral resolutions in the visible and near-infrared regions that are comparable to commonly used polar-orbiting sensors like the Moderate Resolution Imaging Spectroradiometer (MODIS), Visible Infrared Imaging Radiometer Suite (VIIRS), or Landsat. These advances extend applications of geostationary Earth observations from weather monitoring to multiple disciplines in ecology and environmental science. We review a number of existing applications that use data from geostationary platforms and present upcoming opportunities for observing key ecosystem properties using high-frequency observations from the Advanced Baseline Imagers (ABI) on the Geostationary Operational Environmental Satellites (GOES), which routinely observe the Western Hemisphere every 5–15 min. Many of the existing applications in environmental science from ABI are focused on estimating land surface temperature, solar radiation, evapotranspiration, and biomass burning emissions along with detecting rapid drought development and wildfire. Ongoing work in estimating vegetation properties and phenology from other geostationary platforms demonstrates the potential to expand ABI observations to estimate vegetation greenness, moisture, and productivity at a high temporal frequency across the Western Hemisphere. Finally, we present emerging opportunities to address the relatively coarse resolution of ABI observations through multisensor fusion to resolve landscape heterogeneity and to leverage observations from ABI to study the carbon cycle and ecosystem function at unprecedented temporal frequency.

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5 Citations


Journal ArticleDOI: 10.1016/J.FORPOL.2021.102563
Abstract: Overall decline of global burned area paradoxically hides a number of economic realities that have increased the likelihood and costs of wildfire-caused disasters. In this critical review, we address the pressing need to identify and incorporate economic elements shaping global wildfire activities. To synthesize our current understanding of economic drivers of wildfires, we leverage the DPSIR framework to structure the issues related to wildfires to establish coherent causal pathways between Drivers (D), Pressures (P), States (S), Impacts (I) and Responses (R). We identified global patterns of worsening wildfire risks with the double-exposure to globalization and climate change. Current developments call for a paradigm shift in how we understand and manage wildfires to promote an adaptation-mitigation-resilience strategy. We propose expanding the science-policy interface to global scale with new indicators for assessing and communicating the impacts of global economic drivers on wildfire activities, such as “Virtual wildfire trade” accounting to monitor delocalized fire activity—exported fires and land transformation from developed to developing regions with weak governance. We also identified the areas where research is lacking, highlighting future research areas in wildfire economics to advance effective, efficient, and equitable global governance of wildfires.

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Topics: DPSIR (56%), Global governance (53%)

4 Citations


Open accessPosted ContentDOI: 10.5194/ACP-21-16277-2021
Jonathan E. Hickman1, Niels Andela2, Niels Andela3, Enrico Dammers4  +9 moreInstitutions (9)
Abstract: . Atmospheric ammonia (NH 3 ) is a precursor to fine particulate matter and a source of nitrogen (N) deposition that can adversely affect ecosystem health. The main sources of NH 3 – agriculture and biomass burning – are undergoing are or expected to undergo substantial changes in Africa. Although evidence of increasing NH 3 over parts of Africa has been observed, the mechanisms behind these trends are not well understood. Here we use observations of atmospheric NH 3 vertical column densities (VCDs) from the Infrared Atmospheric Sounding Interferometer (IASI) along with other satellite observations of the land surface and atmosphere to evaluate how NH 3 concentrations have changed over Africa from 2008 through 2018, and what has caused those changes. In West Africa NH 3 VCDs are observed to increase during the late dry season, with increases of over 6 % yr −1 in Nigeria during February and March ( p ). These positive trends are associated with increasing burned area and CO trends during these months, likely related to agricultural preparation. Increases are also observed in the Lake Victoria basin region, where they are associated with expanding agricultural area. In contrast, NH 3 VCDs declined over the Sudd wetlands in South Sudan by over 1.5 % yr −1 , though not significantly ( p=0.28 ). Annual maxima in NH 3 VCDs in South Sudan occur during February through May and are associated with the drying of temporarily flooded wetland soils, which favor emissions of NH 3 . The change in mean NH 3 VCDs over the Sudd is strongly correlated with variation in wetland extent in the Sudd: in years when more area remained flooded during the dry season, NH 3 VCDs were lower ( r=0.64 , p ). Relationships between biomass burning and NH 3 may be observed when evaluating national-scale statistics: countries with the highest rates of increasing NH 3 VCDs also had high rates of growth in CO VCDs; burned area displayed a similar pattern, though not significantly. Livestock numbers were also higher in countries with intermediate or high rates of NH 3 VCD growth. Fertilizer use in Africa is currently low but growing; implementing practices that can limit NH 3 losses from fertilizer as agriculture is intensified may help mitigate impacts on health and ecosystems.

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3 Citations


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40 results found


Open accessJournal ArticleDOI: 10.5194/ACP-6-3423-2006
Abstract: Biomass burning represents an important source of atmospheric aerosols and greenhouse gases, yet little is known about its interannual variability or the underlying mechanisms regulating this variability at continental to global scales. Here we investigated fire emissions during the 8 year period from 1997 to 2004 using satellite data and the CASA biogeochemical model. Burned area from 2001–2004 was derived using newly available active fire and 500 m. burned area datasets from MODIS following the approach described by Giglio et al. (2006). ATSR and VIRS satellite data were used to extend the burned area time series back in time through 1997. In our analysis we estimated fuel loads, including organic soil layer and peatland fuels, and the net flux from terrestrial ecosystems as the balance between net primary production (NPP), heterotrophic respiration ( R h ), and biomass burning, using time varying inputs of precipitation (PPT), temperature, solar radiation, and satellite-derived fractional absorbed photosynthetically active radiation (fAPAR). For the 1997–2004 period, we found that on average approximately 58 Pg C year −1 was fixed by plants as NPP, and approximately 95% of this was returned back to the atmosphere via R h . Another 4%, or 2.5 Pg C year −1 was emitted by biomass burning; the remainder consisted of losses from fuel wood collection and subsequent burning. At a global scale, burned area and total fire emissions were largely decoupled from year to year. Total carbon emissions tracked burning in forested areas (including deforestation fires in the tropics), whereas burned area was largely controlled by savanna fires that responded to different environmental and human factors. Biomass burning emissions showed large interannual variability with a range of more than 1 Pg C year −1 , with a maximum in 1998 (3.2 Pg C year −1 ) and a minimum in 2000 (2.0 Pg C year −1 ).

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Topics: Primary production (50%)

1,548 Citations


01 Oct 2003-Earth Interactions
Abstract: The first results of the Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation continuous field algorithm's global percent tree cover are presented. Percent tree cover per 500-m MODIS pixel is estimated using a supervised regression tree algorithm. Data derived from the MODIS visible bands contribute the most to discriminating tree cover. The results show that MODIS data yield greater spatial detail in the characterization of tree cover compared to past efforts using AVHRR data. This finer-scale depiction should allow for using successive tree cover maps in change detection studies at the global scale. Initial validation efforts show a reasonable relationship between the MODIS-estimated tree cover and tree cover from validation sites.

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977 Citations


Open accessJournal ArticleDOI: 10.5194/ESSD-9-697-2017
Abstract: . Climate, land use, and other anthropogenic and natural drivers have the potential to influence fire dynamics in many regions. To develop a mechanistic understanding of the changing role of these drivers and their impact on atmospheric composition, long-term fire records are needed that fuse information from different satellite and in situ data streams. Here we describe the fourth version of the Global Fire Emissions Database (GFED) and quantify global fire emissions patterns during 1997–2016. The modeling system, based on the Carnegie–Ames–Stanford Approach (CASA) biogeochemical model, has several modifications from the previous version and uses higher quality input datasets. Significant upgrades include (1) new burned area estimates with contributions from small fires, (2) a revised fuel consumption parameterization optimized using field observations, (3) modifications that improve the representation of fuel consumption in frequently burning landscapes, and (4) fire severity estimates that better represent continental differences in burning processes across boreal regions of North America and Eurasia. The new version has a higher spatial resolution (0.25°) and uses a different set of emission factors that separately resolves trace gas and aerosol emissions from temperate and boreal forest ecosystems. Global mean carbon emissions using the burned area dataset with small fires (GFED4s) were 2.2 × 1015 grams of carbon per year (Pg C yr−1) during 1997–2016, with a maximum in 1997 (3.0 Pg C yr−1) and minimum in 2013 (1.8 Pg C yr−1). These estimates were 11 % higher than our previous estimates (GFED3) during 1997–2011, when the two datasets overlapped. This net increase was the result of a substantial increase in burned area (37 %), mostly due to the inclusion of small fires, and a modest decrease in mean fuel consumption (−19 %) to better match estimates from field studies, primarily in savannas and grasslands. For trace gas and aerosol emissions, differences between GFED4s and GFED3 were often larger due to the use of revised emission factors. If small fire burned area was excluded (GFED4 without the s for small fires), average emissions were 1.5 Pg C yr−1. The addition of small fires had the largest impact on emissions in temperate North America, Central America, Europe, and temperate Asia. This small fire layer carries substantial uncertainties; improving these estimates will require use of new burned area products derived from high-resolution satellite imagery. Our revised dataset provides an internally consistent set of burned area and emissions that may contribute to a better understanding of multi-decadal changes in fire dynamics and their impact on the Earth system. GFED data are available from http://www.globalfiredata.org .

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Topics: Greenhouse gas (50%)

678 Citations


Open accessJournal ArticleDOI: 10.1016/J.RSE.2016.02.054
Abstract: The two Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, on-board NASA's Terra and Aqua satellites, have provided more than a decade of global fire data. Here we describe improvements made to the fire detection algorithm and swath-level product that were implemented as part of the Collection 6 land-product reprocessing, which commenced in May 2015. The updated algorithm is intended to address limitations observed with the previous Collection 5 fire product, notably the occurrence of false alarms caused by small forest clearings, and the omission of large fires obscured by thick smoke. Processing was also expanded to oceans and other large water bodies to facilitate monitoring of offshore gas flaring. Additionally, fire radiative power (FRP) is now retrieved using a radiance-based approach, generally decreasing FRP for all but the comparatively small fraction of high intensity fire pixels. We performed a Stage-3 validation of the Collection 5 and Collection 6 Terra MODIS fire products using reference fire maps derived from more than 2500 high-resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images. Our results indicated targeted improvements in the performance of the Collection 6 active fire detection algorithm compared to Collection 5, with reduced omission errors over large fires, and reduced false alarm rates in tropical ecosystems. Overall, the MOD14 Collection 6 daytime global commission error was 1.2%, compared to 2.4% in Collection 5. Regionally, the probability of detection for Collection 6 exhibited a ~3% absolute increase in Boreal North America and Boreal Asia compared to Collection 5, a ~1% absolute increase in Equatorial Asia and Central Asia, a ~1% absolute decrease in South America above the Equator, and little or no change in the remaining regions considered. Not unexpectedly, the observed variability in the probability of detection was strongly driven by regional differences in fire size. Overall, there was a net improvement in Collection 6 algorithm performance globally.

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502 Citations


Open accessJournal ArticleDOI: 10.1029/2012JG002128
Abstract: In several biomes, including croplands, wooded savannas, and tropical forests, many small fires occur each year that are well below the detection limit of the current generation of global burned area products derived from moderate resolution surface reflectance imagery. Although these fires often generate thermal anomalies that can be detected by satellites, their contributions to burned area and carbon fluxes have not been systematically quantified across different regions and continents. Here we developed a preliminary method for combining 1-km thermal anomalies (active fires) and 500 m burned area observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) to estimate the influence of these fires. In our approach, we calculated the number of active fires inside and outside of 500 m burn scars derived from reflectance data. We estimated small fire burned area by computing the difference normalized burn ratio (dNBR) for these two sets of active fires and then combining these observations with other information. In a final step, we used the Global Fire Emissions Database version 3 (GFED3) biogeochemical model to estimate the impact of these fires on biomass burning emissions. We found that the spatial distribution of active fires and 500 m burned areas were in close agreement in ecosystems that experience large fires, including savannas across southern Africa and Australia and boreal forests in North America and Eurasia. In other areas, however, we observed many active fires outside of burned area perimeters. Fire radiative power was lower for this class of active fires. Small fires substantially increased burned area in several continental-scale regions, including Equatorial Asia (157%), Central America (143%), and Southeast Asia (90%) during 2001-2010. Globally, accounting for small fires increased total burned area by approximately by 35%, from 345 Mha/yr to 464 Mha/yr. A formal quantification of uncertainties was not possible, but sensitivity analyses of key model parameters caused estimates of global burned area increases from small fires to vary between 24% and 54%. Biomass burning carbon emissions increased by 35% at a global scale when small fires were included in GFED3, from 1.9 Pg C/yr to 2.5 Pg C/yr. The contribution of tropical forest fires to year-to-year variability in carbon fluxes increased because small fires amplified emissions from Central America, South America and Southeast Asia-regions where drought stress and burned area varied considerably from year to year in response to El Nino-Southern Oscillation and other climate modes.

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460 Citations


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