Wildfire strongly influences permafrost environment and soil organic carbon (SOC) pool. In this study, we reviewed the effects of fire severity, time after a fire, and frequency on SOC in boreal permafrost regions. This review highlighted several key points: the effect of wildfires on SOC increased with an increase of fire severity, and the amount of vegetation returned and surface organic matter replenished was less in a short term, which resulted in a significantly lower SOC content compared to that of before the fire. Within a short period after fire, the SOC in near-surface permafrost and the active layer decreased significantly due to the loss of above ground biomass, permafrost thaw, and increased microbial decomposition; as the years pass after a fire, the SOC gradually accumulates due to the contributions of litter layer accumulation and rooting systems from different stages of succession. The increase in fire frequency accelerated permafrost thawing and the formation of thermokarst, resulting in the rapid release of a large amount of soil carbon and reduced SOC storage. Therefore, the study on the effects of wildfires on SOC in the boreal permafrost region is of great significance to understanding and quantifying the carbon balance of the ecosystem.

Recently, as global climate change and local disturbances such as wildfires continue, long- and short-term changes in the high-latitude vegetation systems have been observed in various studies. Although remote sensing technology using optical satellites has been widely used in understanding vegetation dynamics in high-latitude areas, there has been limited understanding of various landscape changes at different spatiotemporal scales, their mutual relationships, and overall long-term landscape changes. The objective of this study is to devise a change monitoring strategy that can effectively observe landscape changes at different spatiotemporal scales in the boreal ecosystems from temporally sparse time series remote sensing data. We presented a new post-classification-based change analysis scheme and applied it to time series Landsat data for the central Yakutian study area. Spectral variability between time series data has been a major problem in the analysis of changes that make it difficult to distinguish long- and short-term land cover changes from seasonal growth activities. To address this issue effectively, two ideas in the time series classification, such as the stepwise classification and the lateral stacking strategies were implemented in the classification process. The proposed classification results showed consistently higher overall accuracies of more than 90% obtained in all classes throughout the study period. The temporal classification results revealed the distinct spatial and temporal patterns of the land cover changes in central Yakutia. The spatiotemporal distribution of the short-term class illustrated that the ecosystem disturbance caused by fire could be affected by local thermal and hydrological conditions of the active layer as well as climatic conditions. On the other hand, the long-term class changes revealed land cover trajectories that could not be explained by monotonic increase or decrease. To characterize the long-term land cover change patterns, we applied a piecewise linear model with two line segments to areal class changes. During the former half of the study period, which corresponds to the 2000s, the areal expansion of lakes on the eastern Lena River terrace was the dominant feature of the land cover change. On the other hand, the land cover changes in the latter half of the study period, which corresponds to the 2010s, exhibited that lake area decreased, particularly in the thermokarst lowlands close to the Lena and Aldan rivers. In this area, significant forest decline can also be identified during the 2010s.

Biomass burning (BB) greatly impacts the Maritime Continent through various mechanisms including agricultural burning, land clearing and natural response to drought. The dynamic characteristics of BB in terms of its spatiotemporal distribution, seasonality, transport mechanism, and aerosol properties have prompted numerous research efforts including field campaigns, in -situ measurements, remote sensing, and modelling. Although the differing perspectives of these studies have offered insights on understanding the regional BB issues, it is challenging to compare and resolve the wider picture because of the diversity of approaches. Human -induced global warming has certainly caused multiple observed changes in the regional meteorological characteristics. In this study, we review BB events in the Maritime Continent from 2012 to 2021, focusing on the meteorological influence and knowledge evolution in cloud -aerosol -radiation (CAR). Unlike other reviews, our review examines the occurrence of BB events using synergistic application of ground -based measurement, global reanalysis model and satellite product, which allows us to examine the anomalies for comparison with other studies and identify the unique features of the event. We identified four dominant modes of variability responsible for the occurrence of large-scale BB in the Maritime Continent: (1) El Nin similar to o Southern Oscillations (ENSO), (2) extreme positiveIndian Ocean Dipole (pIOD), (3) tropical cyclone (TC) activity, and (4) Madden -Julian Oscillations (MJO). We reconcile the past CAR studies and summarize their findings based on the four key CAR mechanisms: (1) instantanous radiative forcing from aerosol -radiation interactions, IRFari (2) and its subsequent adjustments, SAari, (3) instantanous radiative forcing from aerosol -cloud interactions, IRFaci, and (4) and its subsequent adjustments, SAaci. We urge future CAR studies in the Maritime Continent should focus on accurate characterization of the composition of biomass burning plume which is a mixture of peatland, agricultural burning and anthropogenic sources.

Northern high-latitude permafrost holds the largest soil carbon pool in the world. Understanding the responses of permafrost to wildfire is crucial for improving our ability to predict permafrost degradation and further carbon emissions. Recently, studies have demonstrated that wildfires in the pan-Arctic region induced the thickening of the active layer based on site or fire event observations. However, how this induced thickening is influenced by vegetation and permafrost types remains not fully understood due to the lack of wall-to-wall analysis. Therefore, this study employed remotely sensed fire data and modelled active layer thickness (ALT) to identify the fireinduced ALT change (& UDelta;ALT) for the pan-Arctic region, and the contributions of vegetation and permafrost were quantified using the random forest (RF) model. Our results showed that the average & UDelta;ALT and the sensitivity of & UDelta;ALT to burn severity both increased with decreasing ground ice content in permafrost. The largest values were detected in thick permafrost with low ground ice content. Regarding vegetation, the average and sensitivity of & UDelta;ALT in tundra were highest, followed by those in forest and shrub. When the individual environmental factors were all taken into account, the results showed that the contribution of vegetation types was much higher than that of permafrost types (20.2 % vs. 3.5 %). Our findings highlighted the importance of environmental factors in regulating the responses of permafrost to fire.

The impacts of climate change on wildfires have been studied extensively. Along with declining emissions from fossil fuel combustion due to anthropogenic emission control, black carbon (BC) released from wildfires is expected to contribute a more significant portion to its atmospheric burden. However, from a global perspective, little is known about the BC burden and radiative forcing caused by wildfires. Here, we report the results from the long-term wildfire-induced BC concentration and direct radiative forcing (DRF) from 1981 to 2010 globally simulated by an Earth System Model using an updated wildfire BC emission inventory. We show that wildfire-induced BC concentration and DRF varied significantly spatially and temporarily, with the highest in sub-Saharan Africa, attributable to its highest level of wildfire BC emission worldwide. The temporal trends of near-surface air temperature, precipitation, and evapotranspiration and their association with wildfire-induced BC concentration are explored using the multidimensional ensemble empirical mode decomposition. A statistically significant relation between changes in climate parameters and wildfire-induced BC concentration was found for 53% of the land grid cells, explaining on average 33% of the concentration variations. The result suggests that the wildfire-induced BC DRF, with an increasing trend, would be an important contributor to climate change, especially in sub-Saharan Africa. Occurrences of wildfires in the Amazon Basin respond most strongly to climate change and play an increasingly important role in changing the global climate.

Throughout the larch range, warming leads to frequent fires and an increase in burned areas. We test the hypothesis that fires are an essential natural factor that reset larch regeneration and support the existence of larch forests. The study area included Larix sibirica and L. gmelinii ranges within the permafrost zone. We used satellite-derived and field data, dendrochronology, and climate variables analysis. We found that warming led to an increase in fire frequency and intensity, mean, and extreme (>10,000 ha) burned areas. The burned area is increasing in the northward direction, while fire frequency is decreasing. The fire rate exponentially increases with decreasing soil moisture and increasing air temperature and air drought. We found a contrasting effect of wildfire on regeneration within continuous permafrost and within the southern lowland boundary of the larch range. In the first case, burnt areas regenerated via abounded larch seedlings (up to 500,000+ per ha), whereas the south burns regenerated mostly via broadleaf species or turned into grass communities. After the fire, vegetation GPP was restored to pre-fire levels within 3-15 years, which may indicate that larch forests continue to serve as carbon stock. At the southern edge of the larch range, an amplified fire rate led to the transformation of larch forests into grass and shrub communities. We suggested that the thawing of continuous permafrost would lead to shrinking larch-dominance in the south. Data obtained indicated that recurrent fires are a prerequisite for larch forests' successful regeneration and resilience within continuous permafrost. It is therefore not necessary to suppress all fires within the zone of larch dominance. Instead, we must focus fire suppression on areas of high natural, social, and economic importance, permitting fires to burn in vast, larch-dominant permafrost landscapes.

Boreal ecosystems account for 29% of the world's total forested area and contain more carbon than any other terrestrial biome. Over the past 60 years, Alaska has warmed twice as rapidly as the contiguous U.S. and wildfire activity has increased, including the number of fires, area burned, and frequency of large wildfire seasons. These recent and rapid changes in climate and wildfire have implications for future vegetation composition, structure, and biomass in interior Alaska, given that the vegetation is highly dependent on active layer thickness, soil moisture, organic layer depth, and plant-available nutrients. Here we developed a new succession extension (DGS) of the LANDIS-II forest landscape model which integrates a vegetation dynamics model (NECN) with a soil carbon model (DAMM-McNiP), a hydrologic model (SHAW), and a deep soil profile permafrost model (GIPL) in a spatially-explicit framework. DGS Succession uses the algorithms in the NECN Succession extension of LANDIS-II to simulate growth, mortality and reproduction of vegetation but has three major improvements. First, the simple bucket model in NECN was replaced with a physically-based model (SHAW) that simulates energy and water fluxes (e.g. snow depth, evapotranspiration, soil moisture) at multiple levels in the canopy and soil. Second, the active, slow, and passive soil pools in NECN were replaced by seven soil pools that are measurable in the field, with carbon and nitrogen dynamics dictated by DAMM-McNiP. Finally, soil temperature and soil moisture are simulated only at one depth in NECN, but in DGS, soil temperature (and hence permafrost dynamics) are simulated at as many as 50 user-defined depths down to 4 m with SHAW and 75 m with GIPL. During the initial calibration phase, DGS was applied at three inventory sites at the Bonanza Creek Long Term Ecological Research area in Interior Alaska where climate forcings, species biomass, soil temperature, and/or soil moisture were available. For the landscape-scale simulations, DGS was run with the SCRPPLE fire extension of LANDIS-II under two scenarios of climate using a similar to 400,000 ha landscape that included the inventory sites. Across all three sites, DGS generally captured the variation in soil moisture and temperature across depths, seasons, and years reasonably well, though there were some discrepancies at each site. DGS had better agreement with field measurements of soil moisture and temperature than its predecessor NECN which produced unrealistically low soil moisture and unrealistically high seasonal fluctuations in soil temperature. At the landscape scale, ignitions, area burned, and soil temperature increased under climate change, as expected, while soil moisture was relatively unchanged across climate scenarios. Biomass tended to decline under climate change, which differs from other modeling studies in this region but is consistent with the browning trends observed from remote sensing data. Simulating climate, vegetation succession, hydrology, permafrost, carbon and nutrient cycling, and wildfire in an integrated, spatially-explicit framework like LANDIS-II will allow us to disentangle the drivers and ecosystem responses in this rapidly changing ecosystem, as well as other forested systems with complex hydrologic, biochemical, cryospheric, and vegetation feedbacks.

As an active ecological agent in the boreal forest, wildfires have many important impacts on the underlying permafrost. However, investigations of post-fire changes in the features of ecosystem-protected permafrost are extremely limited in the patchy permafrost regions, Northeast China. Additionally, the impacts of wildfires on patchy permafrost are complicated in this region. In this paper, based on field surveys and observations, permafrost features and their influencing factors were analyzed in the area burned in 2006. The results showed notably lower soil temperatures in shrub-wetland (NWH1, unburned and NWH2, light burn) in comparison with those in the birch-larch forest (NWH3, light burn and NWH4, moderate burn). Changes in shallow ground temperatures (0-4 m in depth) were significant. Mean annual soil temperatures (MAST) and annual maximum soil temperature at the light-burn NWH2 site were 0.3-5.2 degrees C higher than those of unburned NWH1, but annual minimum soil temperatures, 0.3-2.1 degrees C lower. MASTs at the moderately burned NWH4 were 0.6-1.6 degrees C higher than those at the light-burn NWH3. The active layer thickness (ALT) was greater at burned sites, and; at the moderately burned site, only seasonal frost was found when 13 years after the burn. The contents of soil organic carbon and total nitrogen were the highest at the unburned NWH1 from 0.0 to 0.4 m in depth, followed by those at the lightly-burned NWH2 and NWH3, and the lowest at the moderately-burned NWH4. Climate warming, forest fires, and changing local factors (e.g., soil moisture contents, snow cover, soil texture and drainage conditions) worked together to increase ground temperature and ALT. These research results could provide important scientific basis for the protection of boreal forest and wetlands and the ecosystem-protected permafrost under a warming climate.

The greenhouse gas (GHG) balance of boreal peatlands in permafrost regions will be affected by climate change through disturbances such as permafrost thaw and wildfire. Although the future GHG balance of boreal peatlands including ponds is dominated by the exchange of both carbon dioxide (CO2) and methane (CH4), disturbance impacts on fluxes of the potent GHG nitrous oxide (N2O) could contribute to shifts in the net radiative balance. Here, we measured monthly (April to October) fluxes of N2O, CH4, and CO2 from three sites located across the sporadic and discontinuous permafrost zones of western Canada. Undisturbed permafrost peat plateaus acted as N2O sinks (-0.025 mg N2O m(-2) d(-1)), but N2O uptake was lower from burned plateaus (-0.003 mg N2O m(-2) d(-1)) and higher following permafrost thaw in the thermokarst bogs (-0.054 mg N2O m(-2) d(-1)). The thermokarst bogs had below-ambient N2O soil gas concentrations, suggesting that denitrification consumed atmospheric N2O during reduction to dinitrogen. Atmospheric uptake of N2O in peat plateaus and thermokarst bogs increased with soil temperature and soil moisture, suggesting sensitivity of N2O consumption to further climate change. Four of five peatland ponds acted as N2O sinks (-0.018 mg N2O m(-2) d(-1)), with no influence of thermokarst expansion. One pond with high nitrate concentrations had high N2O emissions (0.30 mg N2O m(-2) d(-1)). Overall, our study suggests that the future net radiative balance of boreal peatlands will be dominated by impacts of wildfire and permafrost thaw on CH4 and CO2 fluxes, while the influence from N2O is minor.

The emission of black carbon (BC) particles, which cause atmospheric warming by affecting radiation budget in the atmosphere, is the result of an incomplete combustion process of organic materials. The recent wildfire event during the summer 2019-2020 in south-eastern Australia was unprecedented in scale. The wildfires lasted for nearly 3 months over large areas of the two most populated states of New South Wales and Victoria. This study on the emission and dispersion of BC emitted from the biomass burnings of the wildfires using the Weather Research Forecast-Chemistry (WRF-Chem) model aims to determine the extent of BC spatial dispersion and ground concentration distribution and the effect of BC on air quality and radiative transfer at the top of the atmosphere, the atmosphere and on the ground. The predicted aerosol concentration and AOD are compared with the observed data using the New South Wales Department of Planning and Environment (DPE) aethalometer and air quality network and remote sensing data. The BC concentration as predicted from the WRF-Chem model, is in general, less than the observed data as measured using the aethalometer monitoring network, but the spatial pattern corresponds well, and the correlation is relatively high. The total BC emission into the atmosphere during the event and the effect on radiation budget were also estimated. This study shows that the summer 2019-2020 wildfires affect not only the air quality and health impact on the east coast of Australia but also short-term weather in the region via aerosol interactions with radiation and clouds.