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.
Widespread dieback of natural Mongolian pine (Pinus sylvestris var. mongolica) forests in Hulunbuir sandy land since 2018 has raised concerns about their sustainability in afforestation programs. We hypothesized that this dieback is driven by two interrelated mechanisms: (1) anthropogenic fire suppression disrupting natural fire regime, and (2) climate change-induced winter warming reducing snow cover duration and depth. To test these, we quantified dieback using Green Normalized Difference Vegetation Index (GNDVI) across stands with varying fire histories via UAV-based multispectral imagery, alongside long-term climatic observations (1960-2024) of temperature, precipitation, and snow dynamics from meteorological stations combined with remote sensing datasets. Results showed that an abrupt change point in 2018 for both annual precipitation and mean temperature was identified, coinciding with dieback. Significant negative linear relationship between GNDVI (forest health) and last fire interval indicated prolonged fire exclusion exacerbating dieback, possibly via pathogen/pest accumulation. Winter temperature rose significantly during 1960-2023, with notable acceleration following abrupt change point in 1987. Concurrently, winters during 2018-2023 exhibited pronounced warming, with snow cover duration reduced by 23 days and snow depth diminished by 7.6 cm. These conditions reduced snowmelt -derived soil moisture (critical water source) recharge in early spring, exacerbating drought stress during critical growth periods and predisposing trees to pest and disease infestations. Our results support both hypotheses, demonstrating that dieback is synergistically driven by fire regime alteration and climate-mediated snowpack reductions. Converting pure pine forests into mixed pine-broadleaf forests via differentiated water sources was proposed to restore ecological resilience in sandy ecosystems.
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 coupled thermo-hydro-mechanical response caused by fire temperature transfer to surrounding rock/soil has a significant impact on tunnel safety. This study developed a numerical simulation model to evaluate the effects of fire on tunnel structures across different geological conditions. The heat transfer behavior varied with the mechanical properties and permeability of the geotechnics, concentrating within 1.0 m outside the tunnel lining and lasted for 10 days. Significant differences in pore water pressure changes were observed, with less permeable geologies experiencing greater pressure increases. Tunnel deformation was more pronounced in weaker geotechnics, though some tunnels in stronger geologies showed partial recovery post-fire. During the fire, thermal expansion created a bending moment, while a negative bending moment occurred after the fire due to tunnel damage and geotechnical coupling. The entire process led to irreversible changes in the bending moment. The depth of tunnel burial showed varying sensitivity to fire across different geological settings. This study provides important references for fire protection design and post-fire rehabilitation of tunnels under diverse geological conditions.
This study investigates the effects of incorporating date palm wood powder (DPWP) on the thermal, physical, and mechanical properties of lightweight fired earth bricks made from clay and dune sand. DPWP was added in varying proportions (0 %, 5 %, 8 %, 10 %, 12 %, and 15 % by weight of the soil matrix) to evaluate its influence on brick performance, particularly in terms of thermal insulation. Experimental results revealed that adding DPWP significantly reduced the thermal conductivity of the bricks, achieving a maximum reduction of 56.41 %. However, the inclusion of DPWP negatively impacted the physical and mechanical properties of the samples. Among the tested bricks, those with 8 % and 10 % DPWP achieved a desirable balance, maintaining satisfactory mechanical strength within acceptable standards while achieving thermal conductivity values of 0.333 and 0.279 W/m & sdot;K, representing reductions of 37.29 % and 47.46 %, respectively. To further validate these findings, prototypes of the DPWP-enhanced fired bricks and commercial bricks were constructed and tested under real environmental conditions during both summer and winter seasons, over a continuous 12-h daily period. The DPWP-enhanced prototypes demonstrated superior thermal performance, with temperature differences reaching up to 3 degrees C compared to the commercial bricks. These findings highlight the potential of DPWP as a sustainable additive for improving the thermal insulation properties of fired earth bricks, thereby promoting eco-friendly and energy-efficient building materials for sustainable construction practices.
Wildfires are increasingly recognized as a critical driver of ecosystem degradation, with post-fire hydrological and soil impacts posing significant threats to biodiversity, water quality, and long-term land productivity. In fire-prone regions, understanding how varying fire intensities exacerbate runoff and erosion is essential for guiding post-fire recovery and sustainable land management. The loss of vegetation and changes in soil properties following fire events can significantly increase surface runoff and soil erosion. This study investigates the effects of varying fire intensities on runoff and sediment yield in the Kheyrud Educational Forest. Controlled burns were conducted at low, moderate, and high intensities, along with an unburned plot serving as the control. For each treatment, three replicate plots of 2 m2 were established. Runoff and sediments were measured over the course of 1 year under natural rainfall. In addition, key soil physical properties, including bulk density, penetration resistance, and particle size distribution (sand, silt, and clay fractions), were assessed to better understand the underlying mechanisms driving hydrological responses. The results revealed that bulk density and penetration resistance were lowest in the control and highest for the high-intensity fire treatment. A significant correlation was observed between bulk density, penetration resistance, and both runoff and sediment production. However, no significant correlation was found between runoff and soil texture (sand, silt, and clay content). Fire intensity had a pronounced effect on runoff and sediment, with the lowest levels recorded in the control and low-intensity fire treatment, and the highest in the high-intensity fire treatment. The total annual erosion rates were 0.88, 1.10, 1.57, and 2.24 tons/ha/year for the control, low-, moderate-, and high-intensity treatments, respectively. The study demonstrates that high-intensity fires induce substantial changes in soil structure and vegetation cover, exacerbating runoff and sediment loss. To mitigate post-fire soil degradation, proactive forest management strategies are essential. Preventive measures-such as reducing fuel loads (e.g., removing uprooted trees in beech stands), minimizing soil compaction and vegetation damage during logging operations, can help reduce the ecological impact of wildfires. These findings provide a scientific basis for adaptive management in fire-prone forests, addressing urgent needs to balance ecological resilience and human activities in wildfire-vulnerable landscapes.
This study explored the effects of forest fires on soil microbial activity in forest soils classified by rock origin (igneous, metamorphic, and sedimentary) and stratified by subsoil depth (topsoil, subsoil). Microbial activity, indicated by average well color development (AWCD) and Shannon diversity indices, was higher in undamaged topsoils compared to fire-damaged ones. In contrast, fire-damaged subsoils, particularly in metamorphic and sedimentary soils, exhibited increased microbial activity over time due to organic matter decomposition. A significant increase in substrate utilization was observed in undamaged soils across all rock types (*p < 0.05, **p < 0.01) in topsoil, with sedimentary rock exhibiting the highest microbial diversity based on Shannon indices. The dehydrogenase activity followed a similar pattern, with reduced activity in fire-damaged topsoil but higher activity in damaged metamorphic and sedimentary subsoils. Principal component analysis (PCA) linked microbial indicators (AWCD, Shannon index) to mineral compositions like orthoclase and hornblende, highlighting the role of soil chemistry in shaping microbial responses to fire. These insights advance the understanding of fire-induced changes in soil microbial functions across diverse geological contexts.
