Wildfires In Alaska Research Articles

Mental health during wildfires in Southcentral Alaska: An assessment of community-derived mental health categories, interventions, and implementation considerations

Previous studies have linked wildfires to a range of adverse mental health outcomes, but there has been limited research on the mental health impacts of wildfire in Alaska, an area undergoing rapid environmental change. We used a multi-level qualitative approach to identify mental health and psychosocial problems, coping, existing support, and gaps in support among communities who were affected by the Swan Lake and McKinley fires in Alaska in 2019. We recruited 39 community members from Anchorage and the Kenai Peninsula to participate in free list interviews, a community ranking workshop, and in-depth interviews, and we recruited 12 professional key informants including wildland firefighters, mental health providers, community advocates, policy makers, and public health professionals to participate in in-depth interviews and a discussion-based workshop. There were several locally-defined categories of mental health issues identified in relation to wildfires in southcentral Alaska in 2019. Key informants who work in the region identified a package of communications-related interventions as being the most impactful and actionable support for wildfire-related mental health concerns. Additional highly rated mental health supports centered around leadership acknowledging the connection between wildfire and mental health, connecting community members to formal or informal systems of mental health care, enhancing the emergency shelter system, and providing crises debriefing during wildfire evacuations. The results of this study can be utilized to facilitate implementation of prevention and response activities to support mental health resilience during wildfires in Alaska and other wildfire-affected regions.

Forcing the Global Fire Emissions Database burned-area dataset into the Community Land Model version 5.0: impacts on carbon and water fluxes at high latitudes

Abstract. Wildfires influence not only ecosystems but also carbon and water fluxes on Earth. Yet, the fire processes including the occurrence and consequences of fires are still limitedly represented in land surface models (LSMs). In particular, the performance of LSMs in estimating burned areas across high northern latitudes is poor. In this study, we employed the daily burned areas from the satellite-based Global Fire Emissions Database (version 4) (GFED4) into the Community Land Model (version 5.0) with a biogeochemistry module (CLM5-BGC) to identify the effects of accurate fire simulation on carbon and water fluxes over Alaska and Eastern Siberia. The results showed that the simulated carbon emissions with burned areas from GFED4 (i.e., experimental run) were significantly improved in comparison to the default CLM5-BGC simulation, which resulted in opposite signs of the net ecosystem exchange for 2004, 2005, and 2009 over Alaska between the default and experimental runs. Also, we identified that carbon emissions were more sensitive to the wildfires in Alaska than in Eastern Siberia, which could be explained by the vegetation distribution (i.e., tree cover ratio). In terms of water fluxes, canopy transpiration in Eastern Siberia was relatively insensitive to the size of the burned area due to the interaction between leaf area and soil moisture. This study uses CLM5-BGC to improve our understanding of the role of burned areas in ecohydrological processes at high latitudes. Furthermore, we suggest that the improved approach will be required for better predicting future carbon fluxes and climate change.

Spatial proximity to wildfires as a proxy for measuring PM2.5: A novel method for estimating exposures in rural settings.

Climate change impacts humans and society both directly and indirectly. Alaska, for example, is warming twice as fast as the global mean, and researchers are starting to grapple with the varied and inter-connected ways in which climate change affects the people there. With the number of wildfires increasing in Alaska as a result of climate change, the number of asthma cases has increased, driven by exposure to small particulate matter. However, it is not clear how far away smoke from wildfires can affect health. In this study, we hope to establish a relationship between proximity to wildfires and asthma in locations where direct PM2.5 measurement is not easily accomplished. In this study, we examined whether proximity to wildfire exposure is associated with regional counts of adults with asthma, calculated using Behavioral Risk Factor Surveillance System (BRFSS) survey data and US Census data. We assigned "hotspots" around population centers with a range of various distances to wildfires in Alaska. We found that wildfires are associated with asthma prevalence, and the association is strongest within 25 miles of fires. This study highlights the fact that proximity to wildfires has potential as a simple proxy for actual measured wildfire smoke, which has important implications for wildfire management agencies and for policy makers who must address health issues associated with wildfires, especially in rural areas.

Sled dogs as a model for PM2.5 exposure from wildfires in Alaska.

Particulate matter 2.5 (PM2.5) exposure induces oxidative stress associated with many negative health outcomes such as respiratory disorders, cardiovascular disease and neurodegenerative disease. Research shows that diet and exercise can improve antioxidant defense against oxidative stress. This study is the first to use an Arctic animal model to investigate the cumulative effects of two lifestyle interventions on the antioxidant response before, during, and after ambient PM 2.5 exposure from wildfire: antioxidant supplementation (Arthrospira platensis) and exercise. In a two-factorial, longitudinal design, this study divided sled dogs (n=48) into four groups (exercise and supplemented, exercise, supplemented, and control) to (1) test the effects of a 30-day exercise and antioxidant supplementation protocol on antioxidant response; and (2) measure the antioxidant response of all groups during and after a natural wildfire event. Commercial assays for total antioxidant power (TAP) and the enzymatic antioxidant superoxide dismutase (SOD) were used as markers for antioxidant status and response. During the forest fire, SOD was increased 5- to 10-fold over pre/post-exposure levels in all groups suggesting an endogenous upregulation of defense systems in response to the acute environmental stress. TAP was lower in all groups at peak PM2.5 exposure compared to 48h after peak exposure in all groups except the exercise alone group which may indicate that exercise offers improved endogenous defense.

Spatio-temporal patterns of optimal Landsat data for burn severity index calculations: Implications for high northern latitudes wildfire research

Satellite remote sensing has been widely used for the evaluation of wildfire burn severity in various ecosystems. While a variety of remote sensing-based burn severity indices have been developed, the Landsat-based differenced Normalized Burn Ratio (dNBR) presents the most widely-used approach to burn severity assessment for fire research and management. Although dNBR-based approaches have been continuously updated, including the development of the relative dNBR (RdNBR) and the Relativized Burn Ratio (RBR), one key obstacle for the reliable applications of the burn severity indices in the high northern latitudes has not been adequately addressed. Specifically, optimal Landsat image pairs are very rarely available for the calculation of the burn severity indices in certain regions of the high northern latitudes (HNL), resulting in the burn severity index outputs calculated for a large number of wildfires being considerably affected by non-fire-related factors. The suboptimal selection of image pairs may have partially contributed to the lack of consistency in the performance of the burn severity indices in the HNL regions. In this paper, we systematically evaluated the impacts of suboptimal image pairs on signal stability through two sets of analyses conducted at different spatial scales. First, at the regional scale, we examined the burn severity indices calculated for a selection of wildfires in Alaska. Here, we demonstrate the inconsistent performance of the same index calculated based on Landsat data that are typically considered as “optimal”. In addition, we show that the calculated indices may be more prone to the negative impacts of these inconsistencies, thus leading to reduced reliability, when there is limited Landsat data availability. Second, at the continental scale, we show that certain areas in the HNL, especially Alaska during the pre-2000 era, are subject to the potentially strong negative impact associated with the limited data availability. Through systematically analyzing this issue, we hope to not only divert more attention to it but also to provide potential solutions, based on which further improvements that may be of particular importance for research on Arctic wildfires could be made.

Changes in Growing Season Phenology Following Wildfires in Alaska

Trends and geographic patterns of change in vegetation phenology metrics and snowmelt timing from the MODerate resolution Imaging Spectroradiometer (MODIS) satellite data sets were analyzed across the state of Alaska for all wildfires that burned during the years 2004 and 2005. Phenology metric patterns (over the period 2000 to 2018) derived from the normalized difference vegetation index (NDVI) time-series at 250-m resolution tracked changes in the growing season length and integrated greenness cover over the past two decades. NDVI metrics showed that end of the growing season timing (EOST) and integrated greenness increased significantly in the majority of severely burned areas in Interior Alaska over the past decade particularly in low elevation zones below 500 m. In years with relatively early snowmelt dates (3 to 10 days earlier than the long-term mean), lower plant growth was observed over the ensuing growing season, potentially due to lower snow water inputs that can maintain available soil moisture levels for plant growth into the mid- and late-summer months. Statewide trends in MODIS phenology metrics indicate that the predominant vegetation cover type in most regrowing burned areas of Interior Alaska a decade post-fire is still deciduous shrub and young tree cover. Several large fires of special interest were identified to monitor with remote sensing and continue to track long-term recovery patterns and rates.

Isolating different natural and anthropogenic PAHs in the sediments from the northern Bering-Chukchi margin: Implications for transport processes in a warming Arctic

Polycyclic aromatic hydrocarbons (PAHs) have become the dominating burden in the Arctic ecosystems, but their transport pathways and relative importance of different sources in the Arctic remained unclear, and this would be further complicated by climate change. Here we interpreted 27 PAHs in 34 surface sediments from the northern Bering-Chukchi margin. We integrated source apportionment methods (including diagnostic ratios, principal component analysis, hierarchical analysis, and positive matrix factorization (PMF) model) together with geochemistry parameters, which reveal a gradually clear picture of the spatial patterns of different sources. The total PAH concentrations (50.4 to 896.0 ng/g dw) exhibited a “hilly” shape with the increase of latitude, showing the highest level of PAHs in the northeast Chukchi Sea. The total BaP toxic equivalent quotient (TEQ) for carcinogenic compounds was from 1.06 to 33.3 ng TEQ/g. Most PAHs showed positive correlations with silt content, total organic carbon, stable carbon isotopes and black carbon (p < 0.01 or 0.05). Generally, source apportionment methods revealed an increasing petrogenic source of PAHs with latitudes. The PMF model further differentiated two petrogenic (36.7%), two pyrogenic (softwood and fossil fuel combustion, 35.5%) and one in-situ biogenic source (Perylene, 27.8%). An extremely high petrogenic signal was captured in the Canada Basin margin, possibly originating from the Mackenzie River via ice drifting with Beaufort Gyre, while another petrogenic source may come from coal deposit erosion by deglaciation. Softwood combustion (characterized by Retene) exhibited exclusively higher contribution in the northeast Chukchi Sea and might result from the increasing wildfire in Alaska due to climate change, whereas fossil fuel combustion exhibited similar contributions across different latitudes. Our results revealed natural PAHs as important “inside sources” in the Arctic, which are highly sensitive to global warming and deserves more attention.

Fire detection and temperature retrieval using EO-1 Hyperion data over selected Alaskan boreal forest fires

Infrared imaging spectrometers are used to map and characterize wildland fire based on their sensitivity to fire-emitted thermal radiation and ability to resolve spectral emission or absorption features. There is a general paucity of research on the use of space-borne imaging spectroscopy to study active fires in the North American boreal forest. We used hyperspectral data acquired by the Hyperion sensor on the EO-1 satellite over three wildfires in Alaska’s boreal forest to evaluate three fire detection methods: a metric to detect an emission feature from potassium emitted by biomass burning; a continuum-interpolated band ratio (CIBR) that measures the depth of a carbon dioxide absorption line at 2010 nm; and the Hyperspectral Fire Detection Index (HFDI), which is a normalized difference index based on spectral radiance in the short-wave infrared range. We found that a modified version of the HFDI produces a well-defined map of the active fire areas. The CO2 CIBR, though affected by sensor noise and smoke, contributes a slight improvement to the fire detection performance when combined with HFDI-type indices. In contrast, detecting a fire signal from potassium emission was not reliably possible in a practically useful way. We furthermore retrieved fire temperatures by modeling the at-sensor radiance as a linear mixture of two emitted and two reflected spectral radiance endmembers. High-temperature fire areas (the high-intensity fire front, modeled at 800–900 K) and low-temperature combustion (residual fire at 500–600 K), were mapped. High-temperature burning areas as small as half a percent of a Hyperion pixel (approx. 5 m2) were detectable. These techniques are of potential interest for fire characterization in the boreal areas of the circumpolar North using current and future satellite-borne imaging spectrometers.

Fire Severity Filters Regeneration Traits to Shape Community Assembly in Alaska’s Boreal Forest

Disturbance can both initiate and shape patterns of secondary succession by affecting processes of community assembly. Thus, understanding assembly rules is a key element of predicting ecological responses to changing disturbance regimes. We measured the composition and trait characteristics of plant communities early after widespread wildfires in Alaska to assess how variations in disturbance characteristics influenced the relative success of different plant regeneration strategies. We compared patterns of post-fire community composition and abundance of regeneration traits across a range of fire severities within a single pre-fire forest type– black spruce forests of Interior Alaska. Patterns of community composition, as captured by multivariate ordination with nonmetric multidimensional scaling, were primarily related to gradients in fire severity (biomass combustion and residual vegetation) and secondarily to gradients in soil pH and regional climate. This pattern was apparent in both the full dataset (n = 87 sites) and for a reduced subset of sites (n = 49) that minimized the correlation between site moisture and fire severity. Changes in community composition across the fire-severity gradient in Alaska were strongly correlated to variations in plant regeneration strategy and rooting depth. The tight coupling of fire severity with regeneration traits and vegetation composition after fire supports the hypothesis that disturbance characteristics influence patterns of community assembly by affecting the relative success of different regeneration strategies. This study further demonstrated that variations in disturbance characteristics can dominate over environmental constraints in determining early patterns of community assembly. By affecting the success of regeneration traits, changes in fire regime directly shape the outcomes of community assembly, and thus may override the effects of slower environmental change on boreal forest composition.

Carbon and hydrogen stable isotopic ratios of methane emitted from wetlands and wildfires in Alaska: Aircraft observations and bonfire experiments

[1] To investigate spatial variations of CH4 concentration, δ13CH4, and δD-CH4 over Alaska, aircraft observations were conducted during the summer of 2006. CH4 concentrations elevated above the background level were observed over areas with wetlands and wildfires, important sources of CH4. Several flights showed elevated CH4 values, with corresponding δ13CH4 and δD-CH4 signatures of −63.4‰ ± 3.0‰ and −424‰ ± 79‰, respectively, which are based on the relationship between δ13CH4 (or δD-CH4) and CH4 concentration (single mixing relation), an indication of wetland source. It was also noted that both wetlands and wildfires influenced the CH4 concentrations observed over the wildfire area. Assuming certain emission ratios of CH4 to CO (ERCH4/CO) for the wildfire and certain values of δ13CH4 and δD-CH4 for wetland CH4, we derived δ13CH4 and δD-CH4 of CH4 emitted from the wildfire to be −27.5‰ ± 2.0‰ and −285‰ ± 111‰, respectively, which agreed relatively well with, but was slightly lower than, those obtained by previous studies at lower latitudes. To verify these estimates, bonfire experiments were conducted in the interior of Alaska using the same biomass material burned in the wildfire observed by the aircraft. The result showed that the previously reported ERCH4/CO value was plausible and that δ13CH4 and δD-CH4 obtained by the bonfire experiments agreed with the estimates by the aircraft observations. We also found that δ13CH4 and δD-CH4 values became enriched with increasing combustion efficiency. By using the relationship between δD-CH4 for biomass burning and δD of precipitation, global average of δD-CH4 emitted from biomass burning was estimated to be −204‰ ± 11‰.

Relative importance of weather and climate on wildfire growth in interior Alaska

Efforts to quantify relationships between climate and wildfire in Alaska have not yet explored the role of higher-frequency meteorological conditions on individual wildfire ignition and growth. To address this gap, meteorological data for 665 large fires that burned across the Alaskan interior between 1980 and 2007 were assessed to determine the respective influence of higher-frequency weather and lower-frequency climate, in terms of both antecedent and post-ignition conditions on fire growth. Antecedent climate exhibited no discernable influence on eventual fire size. In contrast, fire size was sensitive to weather in the days to weeks following ignition, particularly the post-ignition timing of precipitation. Prolonged periods of warm and dry conditions coincident with blocking that persists for several weeks after ignition enabled growth of large wildfires, whereas the return of wetting precipitation generally within a week after ignition inhibited growth of smaller wildfires. These results suggest that daily weather data are a critical predictor of fire growth and large fire potential and encourage their use in fire management and modelling.

A satellite observation system simulation experiment for carbon monoxide in the lowermost troposphere

We demonstrate the feasibility of using observing system simulation experiment (OSSE) studies to help define quantitative trace gas measurement requirements for satellite missions and to evaluate the expected performance of proposed observing strategies. The 2007 U.S. National Research Council Decadal Survey calls for a geostationary (GEO) satellite mission for atmospheric composition and air quality applications (Geostationary Coastal and Air Pollution Events Mission (GEO‐CAPE)). The requirement includes a multispectral (near‐infrared and thermal infrared) measurement of carbon monoxide (CO) at high spatiotemporal resolution with information on lowermost troposphere concentration. We present an OSSE to assess the improvement in surface CO characterization that would result from the addition of a GEO‐CAPE CO measurement to current low Earth orbit (LEO) thermal infrared‐only measurements. We construct instrument simulators for these two measurement scenarios and study the case of July 2004 when wildfires in Alaska and Canada led to significant CO pollution over the contiguous United States. Compared to a control experiment, an ensemble‐based data assimilation of simulated satellite observations in a global model leads to improvements in both the surface CO distributions and the time evolution of CO profiles at locations affected by wildfire plumes and by urban emissions. In all cases, an experiment with the GEO‐CAPE CO measurement scenario (overall model skill of 0.84) performed considerably better than the experiment with the current LEO/thermal infrared measurement (skill of 0.58) and the control (skill of 0.07). This demonstrates the advantages of increased sampling from GEO and enhanced measurement sensitivity to the lowermost troposphere with a multispectral retrieval.

Increasing Wildfire in Alaska's Boreal Forest: Pathways to Potential Solutions of a Wicked Problem

Recent global environmental and social changes have created a set of “wicked problems” for which there are no optimal solutions. In this article, we illustrate the wicked nature of such problems by describing the effects of global warming on the wildfire regime and indigenous communities in Alaska, and we suggest an approach for minimizing negative impacts and maximizing positive outcomes. Warming has led to an increase in the areal extent of wildfire in Alaska, which increases fire risk to rural indigenous communities and reduces short-term subsistence opportunities. Continuing the current fire suppression policy would minimize these negative impacts, but it would also create secondary problems near communities associated with fuel buildup and contribute to a continuing decline in subsistence opportunities. Collaborations between communities and agencies to harvest flammable fuels for heating and electrical power generation near communities, and to use wildland fire for habitat enhancement in surrounding forests, could reduce community vulnerability to both the direct and the indirect effects of global climate change.

Human Influences on Wildfire in Alaska from 1988 through 2005: An Analysis of the Spatial Patterns of Human Impacts

AbstractBoreal ecosystems in Alaska are responding to climate change in many ways, including changes in the fire regime. While large-scale wildfires are an essential part of the boreal forest ecosystem, humans are changing fire regimes through ignition and suppression. The authors analyzed the impact humans have on fire ignitions and relative area burned with distance into the forest from human access points such as settlements, highways, and major rivers in Alaska from 1988 to 2005. Additionally, a fire prediction model was created to identify drivers for lightning fires in the boreal forest. Human presence increases the number of ignitions near settlements, roads, and rivers and appears to reduce the area burned within 30–40 km of villages and rivers. In contrast to fires near roads and rivers, human presence may somewhat increase the area burned within 30–40 km of highways. The fire prediction model indicated that the probability of fire increases as distance from human settlements increases. In contrast, the model indicated that the probability of fire decreases as distance from roads increases and that the probability of fire in relation to distance from rivers depends on the year of analysis. While the ecological consequences of these human impacts are still unclear, this research shows that human influences on fire regime clearly affect the pattern of fire within 40 km of settlements, which is an area that represents 31% of interior Alaska. Future research should focus on more completely understanding the role of human presence in the suppression of wildfires in interior Alaska.

Impact of the summer 2004 Alaska fires on top of the atmosphere clear‐sky radiation fluxes

In this study we estimate the radiative impact of wildfires in Alaska during the record wildfire season of 2004 by integrating model simulations and satellite observations of the top of the atmosphere (TOA) radiative fluxes and aerosol optical depth. We compare results for the summer of 2004 to results for the summer of 2000 when fire activity in the boreal zone was low. Both observations and model show a decrease in TOA clear‐sky fluxes over the Alaska fire region during summer 2004 of −7 ± 6 W m−2 and −10 ± 4 W m−2, respectively. About two thirds of the change occurs in the longwave, and one third in the shortwave, spectral range. On the bases of detailed model analysis we estimate that the changes in the longwave flux are predominantly explained by a higher surface temperature in summer 2004 compared to 2000. The change in the shortwave flux is largely caused by scattering of solar radiation on organic carbon aerosols emitted from the 2004 fires. This cooling is somewhat mitigated by the warming effect due to absorbing black carbon aerosols emitted from the fires and to a lesser extent by ozone and other greenhouse gases produced and released from the fires. Sensitivity studies with varying aerosol emission scenarios indicate that the ratio of black to organic carbon aerosol emissions of the boreal fires used in this study needs to be increased considerably to match both observations of aerosol optical depth and TOA radiation fluxes, or the biomass burning aerosols must be considerably more absorbing than parameterized in the model. While this study cannot resolve the cause of this discrepancy, it presents a powerful methodology to constrain aerosol emissions. This methodology will benefit from future improvements in measurements and modeling techniques.

Particle size-dependent radical generation from wildland fire smoke

Firefighting, along with construction, mining and agriculture, ranks among the most dangerous occupations. In addition, the work environment of firefighters is unlike that of any other occupation, not only because of the obvious physical hazards but also due to the respiratory and systemic health hazards of smoke inhalation resulting from combustion. A significant amount of research has been devoted to studying municipal firefighters; however, these studies may not be useful in wildland firefighter exposures, because the two work environments are so different. Not only are wildland firefighters exposed to different combustion products, but their exposure profiles are different. The combustion products wildland firefighters are exposed to can vary greatly in characteristics due to the type and amount of material being burned, soil conditions, temperature and exposure time. Smoke inhalation is one of the greatest concerns for firefighter health and it has been shown that the smoke consists of a large number of particles. These smoke particles contain intermediates of hydrogen, carbon and oxygen free radicals, which may pose a potential health risk. Our investigation looked into the involvement of free radicals in smoke toxicity and the relationship between particle size and radical generation. Samples were collected in discrete aerodynamic particle sizes from a wildfire in Alaska, preserved and then shipped to our laboratory for analysis. Electron spin resonance was used to measure carbon-centered as well as hydroxyl radicals produced by a Fenton-like reaction with wildfire smoke. Further study of reactive oxygen species was conducted using analysis of cellular H 2O 2 generation, lipid peroxidation of cellular membranes and DNA damage. Results demonstrate that coarse size-range particles contained more carbon radicals per unit mass than the ultrafine particles; however, the ultrafine particles generated more OH radicals in the acellular Fenton-like reaction. The ultrafine particles also caused significant increases in H 2O 2 production by monocytes and lipid peroxidation. All particle sizes showed the ability to cause DNA damage. These results indicate that the radical generation and the damage caused by them is not only a function of surface area but is also influenced by changing chemical and other characteristics due to particle size.

Ozone production from the 2004 North American boreal fires

We examine the ozone production from boreal forest fires based on a case study of wildfires in Alaska and Canada in summer 2004. The model simulations were performed with the chemistry transport model, MOZART‐4, and were evaluated by comparison with a comprehensive set of aircraft measurements. In the analysis we use measurements and model simulations of carbon monoxide (CO) and ozone (O3) at the PICO‐NARE station located in the Azores within the pathway of North American outflow. The modeled mixing ratios were used to test the robustness of the enhancement ratio ΔO3/ΔCO (defined as the excess O3 mixing ratio normalized by the increase in CO) and the feasibility for using this ratio in estimating the O3 production from the wildfires. Modeled and observed enhancement ratios are about 0.25 ppbv/ppbv which is in the range of values found in the literature and results in a global net O3 production of 12.9 ± 2 Tg O3 during summer 2004. This matches the net O3 production calculated in the model for a region extending from Alaska to the east Atlantic (9–11 Tg O3) indicating that observations at PICO‐NARE representing photochemically well aged plumes provide a good measure of the O3 production of North American boreal fires. However, net chemical loss of fire‐related O3 dominates in regions far downwind from the fires (e.g., Europe and Asia) resulting in a global net O3 production of 6 Tg O3 during the same time period. On average, the fires increased the O3 burden (surface −300 mbar) over Alaska and Canada during summer 2004 by about 7–9% and over Europe by about 2–3%.

Quantifying CO emissions from the 2004 Alaskan wildfires using MOPITT CO data

We present an inverse model analysis to quantify the emissions of wildfires in Alaska and Canada in the summer of 2004 using carbon monoxide (CO) data from the Measurements of Pollution in the Troposphere (MOPITT) remote sensing instrument together with the chemistry transport model MOZART (Model for Ozone and Related Chemical Tracers). We use data assimilation outside the region of the fires to optimally constrain the CO background level and the transport into that region. Inverse modeling is applied locally to quantify the fire emissions. Our a posteriori estimate of the wildfire emissions gives a total of 30 ± 5 Tg CO emitted during June–August 2004 which is of comparable order to the anthropogenic emissions for the continental US. The simulated CO fields have been evaluated by comparison with MOPITT and independent aircraft data.

Fire effects on soil organic matter content, composition, and nutrients in boreal interior Alaska

Boreal ecosystems contain a substantial fraction of the earth's soil carbon stores and are prone to frequent and severe wildfires. In this study, we examine changes in element and organic matter stocks due to a 1999 wildfire in Alaska. One year after the wildfire, burned soils contained between 1071 and 1420 g/m2 less carbon than unburned soils. Burned soils had lower nitrogen than unburned soils, higher calcium, and nearly unchanged potassium, magnesium, and phosphorus stocks. Burned surface soils tended to have higher concentrations of noncombustible elements such as calcium, potassium, magnesium, and phosphorus compared with unburned soils. Combustion losses of carbon were mostly limited to surface dead moss and fibric horizons, with no change in the underlying mineral horizons. Burning caused significant changes in soil organic matter structure, with a 12% higher ratio of carbon to combustible organic matter in surface burned horizons compared with unburned horizons. Pyrolysis gas chromatography – mass spectroscopy also shows preferential volatilization of polysaccharide-derived organic matter and enrichment of lignin- and lipid-derived compounds in surface soils. The chemistry of deeper soil layers in burned and unburned sites was similar, suggesting that immediate fire impacts were restricted to the surface soil horizon.

Variability in the emission of carbon‐based trace gases from wildfire in the Alaskan boreal forest

A study was carried out to assess the variability in trace gas emission from several factors and to estimate the immediate impact of fire on carbon exchange. Using geospatial data, a model of emission was developed for three carbon‐based gases, CO2, CO, and CH4, released during fires from 1950 through 1999 in the boreal region of Alaska. The effect of two factors in the model were investigated: the fractions of carbon consumed and the ratio of flaming to smoldering combustion. We chose 4 years with which to investigate the range of outcomes. An average of 4.5 teragrams of carbon (TgC) has been released annually over the past 50 years. Severe fire years can produce emissions as high as 38 TgC. Wide variations in emissions of total carbon and carbon‐based gas were seen between years. Variations in the estimates of the fractions of biomass consumed during the burn influenced the amount of total carbon emitted; however, the annual area burned strongly determines total carbon released each year, regardless of fraction consumed. Assumptions regarding flaming versus smoldering fire influenced levels of emissions of CO and CH4. These estimates show that wildfire in Alaska's boreal region has contributed a substantial amount of carbon‐based gas to the atmosphere over the five decades of fire records.