Large-scale wildfires are essential sources of black carbon (BC) and brown carbon (BrC), affecting aerosol-induced radiative forcing. This study investigated the impact of two wildfire plumes (Plume 1 and 2) transported to Moscow on the optical properties of BC and BrC during August 2022. During the wildfires, the total light absorption at 370 nm (b(abs_370nm)) increased 2.3-3.4 times relative to background (17.30 +/- 13.98 Mm(-)(1)), and the BrC contribution to total absorption increased from 14 % to 42-48 %. BrC was further partitioned into primary (BrCPri) and secondary (BrCSec) components. Biomass burning accounted for similar to 83-90 % of BrCPri during the wildfires. The b(abs_370nm) of BrCPri increased 5.6 times in Plume 1 and 11.5 times in Plume 2, due to the higher prevalence of peat combustion in Plume 2. b(abs_370nm) of BrCSec increased 8.3-9.6 times, driven by aqueous-phase processing, as evidenced by strong correlations between aerosol liquid water content and b(abs_370nm) of BrCSec. Daytime b(abs_370nm) of BrCSec increased 7.6 times in Plume 1 but only 3.6 times in Plume 2, due to more extensive photobleaching, as indicated by negative correlations with oxidant concentrations and longer transport times. The radiative forcing of BrCPri relative to BC increased 1.8 times in Plume 1 and Plume 2. In contrast, this increase for BrCSec was 3.4 times in Plume 1 but only 2.3 times in Plume 2, due to differences in chemical processes, which may result in higher uncertainty in its radiative forcing. Future work should prioritize elucidating both the emissions and atmospheric processes to better quantify wildfire-derived BrC and its radiative forcing.
Aim Alaska's boreal forest is experiencing increasingly severe fires, droughts, and pest attacks that may destabilize carbon sequestration. Our aim was to understand boreal forest resilience to changing wildfire regimes using remote-sensed datasets validated with ground-truthing (GT).Location Five recently burned boreal forest sites (2010-2019) near Fairbanks, Alaska.Methods We used four AVIRIS-NG hyperspectral image datasets (425 spectral bands at 5-nm intervals; 3.5 x 43 km average swath) imaged by NASA in 2017-2018 during the Arctic-Boreal Vulnerability Experiment (ABoVE). Spectral analysis included fire fuel loads and random forest (RF) models constructed from key bands to describe common pre- and postburned vegetation classes. Models were validated with 89 GT plots inside the AVIRIS scenes. GT included tree stem densities, understory cover, soil characteristics, radial growth of 51 spruce trees from cores, and visual damage assays of 668 conifers and deciduous trees.Results Spectral evidence of high fuel loads in 2017 pre-dated a 2019 wildfire. Post-GT local models described vegetation more accurately than pre-GT, but accuracy decreased when spectral rulesets were broadened to increase overall classification. Soil temperature, basal area, slope, elevation, and tree density varied widely; thaw depth, soil moisture, moss cover, and canopy height varied mainly by vegetation class. Invasive species and thermokarst were insignificant. Deciduous seedlings were abundant in postburned sites; however, conifer seedling densities were similar to unburned forest. Upland spruce radial growth showed earlier drought sensitivity than lowland spruce.Conclusion Spectral analysis revealed fire vulnerability in some areas; however, local and temporal spectral variation presented challenges to accurately classify vegetation in AVIRIS scenes. GT suggests that recovering forests near Fairbanks may lack sufficient conifer recruitment to replace existing stands. Sites with stable seasonal thaw may offset drought stress under global warming.
In recent years, increasing wildfire activity in the western United States has led to significant emissions of smoke aerosols, impacting the atmospheric energy balance through their absorption and scattering properties. Single scattering albedo (SSA) is a key parameter that governs these radiative effects, but accurately retrieving SSA from satellites remains challenging due to limitations in sensor resolution, low sensitivity of traditional remote sensing methods, and uncertainties in radiative transfer modeling, particularly from surface reflectance and aerosol characterization. Smoke optical properties evolve rapidly after emission, influenced by fuel type, combustion conditions, and chemical aging. Accurate SSA retrieval near the source thus requires high-temporal-resolution satellite observations. Critical Reflectance (CR) method provides this capability by identifying a unique reflectance value at which top-of-atmosphere (TOA) reflectance becomes insensitive to aerosol loading and primarily reflects aerosol absorption. SSA can be retrieved from this critical reflectance. This study presents a geostationary-based CR method using the Advanced Baseline Imager (ABI) on GOES-R satellites. The approach leverages ABI's high temporal (5-10 min) and spatial (3 km) resolution, consistent viewing geometry, and wide coverage. A tailored look-up table, based on an AOD-dependent smoke model for North America, links CR to SSA. Case studies show strong agreement with AERONET measurements, with retrieval differences mostly within 0.01-well below AERONET's +/- 0.03 uncertainty. The method captures temporal and spatial variations in smoke absorption and demonstrates robustness across daylight hours. This GEO-based CR approach offers an effective tool for high-resolution SSA retrieval, contributing to improved aerosol radiative forcing estimates and climate modeling.
Permafrost, a critical global cryospheric component, supports subarctic boreal forests but is frequently disturbed by wildfires, an important driver of permafrost degradation. Wildfires reduce vegetation, organic layers, and surface albedo, leading to active layer thickening and ground subsidence. Recent studies using interferometric synthetic aperture radar (InSAR) have confirmed the rapid and extensive post-fire permafrost degradation, and have largely focused on short-term impacts. However, the longer-term post-fire permafrost deformation, potentially persisting for decades, remains poorly understood due to limited data. Here, we applied InSAR in North Yukon to detect deformation signals across multiple fire scars in the past five decades. Using a chronosequence (space-for-time substitution) approach, we summarize a continuous trajectory of post-fire permafrost evolution: (a) an initial degradation stage, characterized by abrupt subsidence up to 50 mm/year and gradually slowing over the first decade, with cumulative subsidence exceeding 100 mm locally; (b) an aggradation stage from approximately 15 to 30 years after fire, marked by ground uplift reaching 25 mm/year before gradually declining, compensating for the earlier subsidence; and (c) a stabilization stage beyond three to four decades, where permafrost nearly recovers to pre-fire conditions with indistinguishable deformation between burned and unburned areas. Notably, the rarely-reported uplift phase appears closely related to vegetation regeneration and fire-greening feedback that provide thermal protection, suggesting a critical mechanism of permafrost recovery. These findings provide new insights into the resilience of boreal-permafrost systems to wildfires and also underscore the importance of long-term InSAR monitoring in understanding permafrost responses to wildfires under climate change.
Atmospheric brown carbon (BrC) from wildfires is a key component of light-absorbing carbon that significantly contributes to global radiative forcing, but its atmospheric evolution and lifetime remain poorly understood. In this study, we investigate BrC evolution by synthesizing data from one laboratory campaign and four aircraft campaigns spanning diverse spatial scales across North America. To estimate initial conditions for evaluating plume evolution, we develop a method to parametrize the emission ratios of BrC and other species using commonly measured inert tracers, acetonitrile and hydrogen cyanide. The evolution of BrC absorption in the free troposphere is characterized as a function of hydroxyl radical (OH) exposure, yielding an effective photochemical rate constant of 9.7-1.6 +4.8 x 10-12 cm3 molecule-1 s-1. The relatively slow reaction rate results in small BrC decay within the first few hours after emission, making it difficult to distinguish from source variability. This helps explain the absence of clear evolutionary trends in near-field studies. Assuming an OH concentration of 1.26 x 106 molecules cm-3, this rate constant corresponds to an e-folding lifetime of approximately 23 h. After extensive photooxidation (OH exposure similar to 1012 molecules cm-3 s), 4 +/- 2% of the emitted BrC persists, representing a recalcitrant fraction with potential long-term climate impacts. These results improve our understanding of BrC variability and photochemical processing and provide critical constraints for modeling its impacts on climate.
The extent of wildfires in tundra ecosystems has dramatically increased since the turn of the 21st century due to climate change and the resulting amplified Arctic warming. We simultaneously studied the recovery of vegetation, subsurface soil moisture, and active layer thickness (ALT) post-fire in the permafrost-underlain uplands of the Yukon-Kuskokwim Delta in southwestern Alaska to understand the interaction between these factors and their potential implications. We used a space-for-time substitution methodology with 2017 Landsat 8 imagery and synthetic aperture radar products, along with 2016 field data, to analyze tundra recovery trajectories in areas burned from 1953 to 2017. We found that spectral indices describing vegetation greenness and surface albedo in burned areas approached the unburned baseline within a decade post-fire, but ecological succession takes decades. ALT was higher in burned areas compared to unburned areas initially after the fire but negatively correlated with soil moisture. Soil moisture was significantly higher in burned areas than in unburned areas. Water table depth (WTD) was 10 cm shallower in burned areas, consistent with 10 cm of the surface organic layer burned off during fire. Soil moisture and WTD did not recover in the 46 years covered by this study and appear linked to the long recovery time of the organic layer.
Wildfires, both natural and man-made, release and mobilize hazardous substances such as heavy metal(loids) (HM), which are known carcinogens. Following intense rainfall events, HM bound to soil organic matter are transported from the soil to surface water, resulting in water quality degradation. This study reviews the pollution status of HM in wildfire-affected soil and surface water, as well as their toxic effects on aquatic organisms and humans. The rate of HM release during wildfires depends on factors such as the type of tree burned and fire severity. The mobility of HM from soil to surface water is influenced by soil pH, organic matter content, rainfall intensity, and duration. The risk priority number (RPN) analysis indicates that both wildfire-affected soil and surface water require remediation to address HM contamination. HM concentrations in both soil and surface water decrease over time due to soil erosion, wind, storm events, and the depletion of burnt residues. The greatest percentage changes in HM concentrations in burned soils compared to unburned soils were observed for vanadium (340%), nickel (260%), and arsenic (110%). In surface water, the highest increases were seen for iron (740%), vanadium (530%), and aluminium (510%). Wildfire-affected water has been shown to cause toxic effects in aquatic organisms, including DNA damage, oxidative stress, and lipid peroxidation. The consumption of HMcontaminated water and fish poses significant health risks to humans. Therefore, post-fire monitoring of wildfireaffected areas is essential for designing treatment plants, assessing risks, and establishing maximum allowable HM concentrations in water.
The recent increase of the air temperature due to the global climate change is considered as one of the important reasons for the wildfires increase in the world, even in areas where the wildfires are not that common. In addition to the various physical damages adversely affecting the ecological balance, harmful gases and solid particles are released into the atmosphere due to wildfires, causing serious health problems. In this study, impacts of the most serious forest fire in modern history of the country lasting 16 days from 23rd of July 2022 in the National Park Bohemian Switzerland in the D & ecaron;& ccaron;& iacute;n district, Czech Republic, were investigated using remote sensing satellite datasets by cloud-based Google Earth Engine (GEE) platform. The normalized difference moisture index (NDMI), normalized burn ratio index (NBR), normalized difference vegetation index (NDVI), land surface temperature (LST) and soil moisture index (SMI) were calculated from Landsat-8 Operational Land Imager and Thermal Infrared Sensor (OLI and TIRS) dataset for the dates of 31st October 2021, 18th June 2022, and 31st October 2022. Relationship of the remote sensing indices were calculated to estimate the impacts of the wildfire. Furthermore, distribution of nitrogen dioxide (NO2) was extracted using Sentinel-5P TROPOMI (Tropospheric Monitoring Instrument) to observe changes before and after the forest fire in the study region. The burnt area approximately 13.20 km2 from the total area of 79.28 km2 was detected using different time series of the remote sensing indices in the national park.
Critically burnt slopes are treated after a wildfire to reduce erosion and the impacts of eroded soil and ash on downstream water quality. Conventional post-wildfire erosion mitigation methods including mulch, barrier, and seeding treatments have some drawbacks that may result in low efficiency. Polymeric materials, xanthan gum (XG) and polyacrylamide (PAM), are shown to be effective alternatives to the conventional methods in controlling post-wildfire erosion of bare soil. This study evaluates the use of XG and PAM for controlling post-wildfire erosion when the soil surface is covered with hydrophilic ash, which is a common scenario after wildfires in moderate to high soil burn severity regions. Indoor rainfall simulation experiments are performed with soil and ash samples collected after the 2021 Green Ridge Wildfire near Walla Walla, WA to determine the effects of three concentrations (11, 33, and 60 kg/ha) of XG and PAM on infiltration, runoff, and sediment loss in ash-covered soil plots during three wet-dry cycles. Results show that XG and PAM treatments reduce the total sediment loss by up to 68% (XG) and 87% (PAM) during three wetting events for the study soil and ash. Both XG and PAM induce partial surface sealing, which results in higher runoff. However, with subsequent wettings, surface sealing reduces due to redistribution of XG and PAM. The results are explained through the distribution of water along plot depth, scanning electron microscope images, and binding of ash and additives.
AimHigh temperatures during forest fires can cause significant damage to tropical dry forest areas and alter their ecological stability, particularly by affecting seed viability and seedling emergence. This study evaluates the seedling emergence response of 18 dry forest species to fire-simulated temperatures, aiming to assess their potential for restoration in fire-prone Colombian ecosystems.LocationThe seeds used in this study were obtained from three tropical dry forests in Colombia.MethodsA total of 9832 seeds from 18 dry forest species were collected directly from the soil seed bank in three tropical dry forests in Colombia. These seeds were then exposed to simulated forest fire temperatures (100 degrees C, 150 degrees C, and 200 degrees C) for 10 min. Seed viability was analyzed using the 2,3,5-triphenyl tetrazolium chloride reagent (tetrazolium test) and assessed using a generalized linear model. Seedling emergence and mean emergence time were evaluated using one-way analysis of variance (ANOVA) with temperature treatments as factors.ResultsThe study revealed that seedling emergence significantly decreased with higher heat shock temperatures. Notably, Hura crepitans and Parkinsonia aculeata tolerated temperatures up to 100 degrees C, while Caesalpinia pulcherrima and Enterolobium cyclocarpum showed increased emergence at that temperature. Based on their emergence responses, species were classified as stimulated, tolerant, sensitive, or vulnerable. Seed viability declined with rising temperatures, and the mean emergence time increased in species like Cordia alba, Crescentia cujete, and Lonchocarpus violaceus.ConclusionsThis study shows that heat shocks at 150 degrees C and 200 degrees C significantly reduced seed bank viability for most Colombian dry forest species. However, Caesalpinia pulcherrima and Enterolobium cyclocarpum were stimulated by 100 degrees C heat shocks, while Hura crepitans and Parkinsonia aculeata showed no adverse effects. Vulnerable species like Coccoloba acuminata and Pithecellobium dulce exhibited no viable seeds at higher temperatures, suggesting potential local extinctions. These results emphasize the need to focus on heat-tolerant species for restoration efforts in fire-prone ecosystems.
