Effects Of Wildfire Research Articles

Notable impact of wildfires in the western United States on weather hazards in the central United States

Increased wildfire events constitute a significant threat to life and property in the United States. Wildfire impact on severe storms and weather hazards is another pathway that threatens society, and our understanding of which is very limited. Here, we use unique modeling developments to explore the effects of wildfires in the western US (mainly California and Oregon) on precipitation and hail in the central US. We find that the western US wildfires notably increase the occurrences of heavy precipitation rates by 38% and significant severe hail (≥2 in.) by 34% in the central United States. Both heat and aerosols from wildfires play an important role. By enhancing surface high pressure and increasing westerly and southwesterly winds, wildfires in the western United States produce (1) stronger moisture and aerosol transport to the central United States and (2) larger wind shear and storm-relative helicity in the central United States. Both the meteorological environment more conducive to severe convective storms and increased aerosols contribute to the enhancements of heavy precipitation rates and large hail. Moreover, the local wildfires in the central US also enhance the severity of storms, but their impact is notably smaller than the impact of remote wildfires in California and Oregon because of the lessened severity of the local wildfires. As wildfires are projected to be more frequent and severe in a warmer climate, the influence of wildfires on severe weather in downwind regions may become increasingly important.

Effects of two firefighting chemical formulations, Phos–Chek LC95W and BlazeTamer380, on striped marsh frog (Limodynastes peronii) tadpole survival, growth, development and behaviour

Global wildfire events are projected to become more frequent and severe due to the continual threat of climate change, resulting in increasing demand for effective fire mitigation methods. Firefighting chemicals (FFCs), including retardants, foams and water enhancers, are often used to prevent the spread of wildfires. However, the impact of FFCs on wildlife and ecosystems is poorly understood. We investigated the effects of two common FFC formulations, Phos-Chek LC95W and BlazeTamer380, on tadpole survival, growth, development and swimming behaviour. Tadpoles of the striped marsh frog (Limnodynastes peronii) were exposed to two concentrations of either Phos-Chek (0.25 and 1 g/L) or BlazeTamer (0.05 and 0.2 g/L) for 16 days. The highest concentration of Phos–Chek was lethal to tadpoles, with mortalities gradually increasing over time and only 8% of animals surviving to day 16. Both FFCs influenced the growth and development of tadpoles, though effects were more severe in tadpoles exposed to the Phos-Chek formulation. Phos-Chek was found to completely stop tadpole growth and development over the 16-day exposure, whereas BlazeTamer significantly delayed growth and development in comparison to controls. Nevertheless, treatments had no apparent effect on tadpole movement patterns and swimming activity. Greater toxicity caused by the Phos-Chek treatment likely relates to the increased ammonia and altered water quality parameters. Runoff or accidental application of commonly used FFCs into small waterways may therefore have important ramifications for aquatic biota.

Probabilistic Wildfire risk assessment methodology and evaluation of a supply chain network

Increasing wildfire risks have significantly disrupted supply chain systems in the United States, which accounts for a large portion of wildfire-induced economic losses and affects the regional and national economies. While it is important to understand wildfire effects on supply chains in meeting customer needs and achieving regional economic stability, such effects have not yet been extensively studied. This paper proposes a probabilistic framework for quantitatively assessing wildfire risk to a supply chain network. It provides rigorous probabilistic descriptions of wildfire ignition likelihood and growth, the interaction between supply chain components and wildfire, consequent component damage, and network-level performance reduction. A hypothetical forest-residuals-to-sustainable-aviation-fuel supply chain network is utilized as an illustrative example to demonstrate the capability and applicability of the proposed framework. The simulation results indicate that wildfire-induced damages to feedstock nodes are insignificant (i.e., 0.1% reduction in total feedstock availability per year), whereas total supply chain cost still increases considerably due to high unmet demand penalty and detours. Moreover, the findings further demonstrate the weakness of network configuration under wildfire risk: a failure of the processing facility located in the Inland Northwest of the United States results in significant increases in total transportation costs and time, which suggests that the construction of additional processors in this region could reduce wildfire risk significantly. Thus, the proposed framework can be used as a planning tool to evaluate network performance subject to a set of what-if scenarios and assess the effect of pre- and post-wildfire risk mitigation measures.

Repeated Wildfires in the Middle Jurassic Xishanyao Formation (Aalenian and Bajocian Ages) in Northwestern China

AbstractThe coal‐bearing strata in the southern Junggar Basin in northwestern China have recently attracted the attention of coal geologists. Its abundance of coal resources is of great interest as there is a potential of unlocking details about the palaeoclimatic information. Coal deposits have the capacity to record wildfire events, even those with inefficient combustions. To characterize wildfire events and palaeoclimatic history of the Middle Jurassic Xishanyao Formation (Aalenian and Bajocian ages), 22 coal samples from borehole cores and coal mines in the southern Junggar Basin were collected and their macerals were analyzed. The results indicated that fusinite and semi‐fusinite were the dominant components of inertinite with proportions of 35.27% and 54.67%, respectively. The presence of inertinite is an indicator that wildfires occurred at the time of peat land development, and the widespread occurrence suggests large scale wildfires during the Middle Jurassic. This study proposes a new parameter for the evaluation of wildfire features by combining burning frequency and burning temperature. The comprehensive evaluation index (CEI) was influenced by the lacustrine basin level and ancient plant types from a sequence framework. During the Middle Jurassic, most wildfires were surface fires with low level and ground fire with high level. High oxygen levels were estimated in the lower, middle, and upper members of the Xishanyao Formation with corresponding to 26.78%, 24.55%, and 23.55%, respectively. The high oxygen levels would be the primary cause of repeated wildfires in the Middle Jurassic. These results are helpful for understanding palaeoclimatic changes in the Middle Jurassic.

Performance evaluation of activated carbon sorbents for indoor air purification during normal and wildfire events.

Volatile organic compounds (VOCs) are a significant class of indoor air pollutants and are known for their adverse effects on health. A common strategy to reduce indoor VOC levels is to use sorbents, including activated carbons (ACs). The amount of activated carbon is critical to achieving a reasonable AC filter lifetime in an air purification device. The study aims to estimate the amount of carbon needed in a typical indoor environment and in a heavy use setting such as during cooking, agriculture field fires, or wildfires. The problem is complex as various types of ACs are used, and the type and concentration of VOCs in the indoor environment also vary in different settings. Therefore, literature data on thermophysical parameters for 45AC-VOC pairs was used to estimate the required amount of AC under a given set of conditions. The study uses modeling distributions of the footprint of suitable carbon filters for the removal of common VOCs encountered indoors for a period of 30 days. It was found that while 50% of AC-VOC pairs surveyed will require about 190-370g at low indoor VOCs levels of 0.1-1μmol/m3(considered a good clean indoor environment), up to 1.1kg of ACs are needed for a carbon filter to survive 30 days in a typical indoor environment (VOCs levels of 10μmol/m3). On the other hand, 3-15kg or more AC will be needed in a filter to survive 30 days during adverse events such as wildfires. The objective of the present study is to aid consumers and businesses in making an informed decision on the type of AC-based indoor air filters that meet their needs. Using this data, an open-access online calculator is being developed to predict the amount of carbon needed in a filter/device at any specific indoor air condition.

Assessing the effects of native and alien plant ash on mosquito abundance.

Plant invasions have been linked to displacement of native vegetation and altering of fire regimes and might influence vector mosquito populations by altering habitats or nutrient inputs. Whereas wildfire effects on terrestrial ecosystems are relatively well‐studied, ash depositions into aquatic ecosystems and effects on semi‐aquatic taxa such as mosquitoes have remained overlooked. Here, we investigated mosquito colonization in water treated with ash from native plants [quinine tree (Rauvolfia caffra), Transvaal milk plum (Englerophytum magalismontanum), apple leaf (Philenoptera violacea)] and invasive alien plants [i.e., lantana (Lantana camara), guava (Psidium guajava), red river gum (Eucalyptus camaldulensis)] in containers at two ash concentrations (i.e., 1, 2 g/L). Overall, there was no statistically clear difference in colonization between ash from native and alien species. We recorded colonization by two mosquito genera (Culex spp. and Anopheles spp.), with Culex generally much more abundant than Anopheles. Few differences were identified among the plants, with statistically clear effects of ash type and concentration on larval and pupal stages. High Culex egg and larval abundances were shown in lantana and apple leaf treatments compared to controls, and milkplum versus controls for pupae of both genera. Further research is required to elucidate the influence of nutrient inputs from different ash species on vector mosquito population dynamics.

Soil Loss Potential Assessment for Natural and Post-Fire Conditions in Evia Island, Greece

A devastating forest fire in August 2021 burned about 517 km2 of the northern part of Evia Island, affecting vegetation, soil properties, sediment delivery and the hydrological response of the catchments. This study focuses on the estimation of the annual soil loss in the study area under natural (pre-fire) and post-fire conditions. The assessment of the soil loss potential was conducted with the application of the Universal Soil Loss Equation (USLE), which is an empirical equation and an efficient way to predict soil loss. The USLE factors include rainfall erosivity (R), soil erodibility (K), the slope and slope length factor (LS), the cover management factor (C) and the erosion control practice factor (P). The USLE quantified the annual soil erosion (in t/ha/year) for both pre- and post-wildfire conditions, and the study area has been classified into various soil loss categories and soil erosion intensity types. The results showed that the annual soil loss before the forest fires ranged from 0 to 1747 t/ha, with a mean value of 253 t/ha, while after the fire the soil loss significantly increased (the highest annual soil loss was estimated at 3255 t/ha and the mean value was 543 t/ha). These values demonstrate a significant post-fire change in mean annual soil loss that corresponds to an increase of 114% compared to the pre-fire natural condition. The area that is undergoing high erosion rates after the extreme wildfire event increased by approximately 7%, while the area of moderate rates increased by 2%. The calculated maximum potential of soil erosion, before and after the 2021 extreme wildfire event, has been visualized on spatial distribution maps of the average annual soil loss for the study area. The present study underlines the significant post-fire increase in soil loss as part of the identification of the more vulnerable to erosion areas that demand higher priority regarding the protective/control measures.

Managing Fire-Adapted Invasive Plants in the American West

Humans impact fire in many ways. They may reduce ignitions by implementing fire suppression protocols or increase fire incidence through accidental or prescriptive ignitions. Anthropogenic changes to climate affect wind speeds and temperature that in turn may translate to more dangerous fire behaviour. Importantly for this discussion, humans also change the species composition of plant communities either directly by moving plant propagules or indirectly by affecting climate which in turn affects the geographical distribution of plants. Largely because of human actions, Western United States have witnessed drastic increases in the geographic distribution and severity of several important fire-adapted exotic plant species including Bromus tectorum (cheatgrass), Cenchrus ciliaris (buffelgrass), Ventenata dubia (ventenata), Taeniatherum caput-medusae (medusahead), Arundo donax (giant reed), and others. A recent United Nations study finds "the management of invasive alien vegetation is crucial for the prevention of extreme wildfires". The increase of invasive plants that are fire-adapted has changed the fire regimes in the American West fundamentally leading to more frequent and intense fires. Altered fire regimes have significant human and environmental-health consequences and threaten the economic sustainability of communities broadly, especially in the wild-land-urban interface. In California, seven of the 20 deadliest fires on record and 11 of the 20 most destructive fires have occurred in the past five years. Exposure to smoke from wildfires can have severe health consequences broadly across the region. Environmental degradation and severe wildfire events associated with exotic plant invasion have had significant impacts on rare, threatened and endangered species.

Deep Learning Provides Substantial Improvements to County‐Level Fire Weather Forecasting Over the Western United States

AbstractThe recent wildfires in the western United States during 2018 and 2020 caused record‐breaking fire damage and casualties. Despite remarkable advances in fire modeling and weather forecasting, it remains challenging to anticipate catastrophic wildfire events and associated damage. One key missing component is a fire weather prediction system with sufficiently long lead time capable of providing useful regional details. Here, we develop a hybrid prediction model of wildfire danger called CFS with super resolution (CFS‐SR) as a proof of concept to fill that void. The CFS‐SR model is constructed by integrating the Climate Forecast System version 2 with a deep learning (DL) technique from Single Image Super Resolution, a method widely used in enhancing image resolution. We show that for the 2018–2019 fire season, the CFS‐SR model significantly improves accuracy in forecasting fire weather at lead times of up to 7 days with an enhanced spatial resolution up to 4 km. This level of high resolution provides county‐level fire weather forecast, making it more practical for allocating resources to mitigate wildfire danger. Our study demonstrates that a proper combination of ensemble climate predictions with DL techniques can boost predictability at finer spatial scales, increasing the utility of fire weather forecasts for practical applications.

Persistent Positive Anomalies in Geopotential Heights Promote Wildfires in Western North America

Abstract During summer, persistent positive anomalies (PPAs) of midtropospheric geopotential heights in North America are often associated with extreme weather, including heatwaves. We evaluate the link between prolonged summertime PPAs in 500-hPa geopotential heights and wildfire activity across western North America and examine temporal trends in PPA characteristics. On average, 17% of May–September days experience PPA events over the study domain. Large fires (burned area > 500 ha) were 7 times as likely to start during a PPA, with approximately 40% of these fires’ ignitions coincident with PPA events. A positive correlation exists between the fraction of May–September PPA days and burned area for most of the study domain. Additionally, the presence of a PPA exerts greater influence on fire ignition and burned area in higher latitudes than lower latitudes of western North America. We find a statistically significant expansion in the spatial extent of PPA events during 1979–2020. The observed expansion of the PPAs is likely due to thermodynamic changes in midlatitude synoptic patterns. These findings may improve our understanding of the connections between PPA events and wildfires in western North America, enhance the short-term predictability of wildfire events, and have important implications for increased fire risk in a warming climate. Significance Statement Persistent positive anomalies (PPAs) of the upper air atmospheric flow, a slow progression of planetary waves, are synoptic-scale patterns that cause heatwaves and contribute to wildfire activity. We seek to understand how these events relate to fire weather and fire activity over western North America. The presence of PPA events increases the likelihood of fire ignition by a factor of 7, with higher likelihood over northern regions. The mean area of the PPA events has grown significantly in recent decades, exposing larger areas and populations to increased fire risks. These results improve our understanding of the connections between upper air atmospheric patterns and wildfires, signal how it may change in future warmer climate and scenarios, and enhance the near-future predictability of fire events in this region.

Polycyclic aromatic hydrocarbons in terrestrial and aquatic environments following wildfire: a review

Wildfires are a natural landscape disturbance in many climates and forest types, but the cumulative impact of human-caused climate change, historical fire management and suppression, and changing species diversity in forests has led to an increase in the size and (or) severity of wildfires in certain regions across the globe. There are a significant number of research studies on the effects of wildfire on human health, forest ecology, hydrology, and the physical, chemical, and biological properties of soils. However, research on the impact of wildfire on watersheds including toxicity in aquatic organisms, water chemistry, and fluvial sediment quality is less extensive, focusing primarily on water quality indicators such as nutrients and sediment flux. Recent research has shown that wildfires contribute to the environment significant amounts of polycyclic aromatic hydrocarbons (PAHs), which are compounds produced during the incomplete combustion of organic material, and are known to be toxic and mutagenic compounds. The primary objective of this paper is to review the recent literature that pertains to the contamination of surface waters and sediments and source apportionment of wildfire-derived PAHs to determine where research gaps remain. Additional objectives are to assess the use of molecular ratios to apportion PAH sources and, finally, to create a roadmap for future studies in designing and conducting research that seeks to determine sources of wildfire-derived PAHs in water and sediment.

Joint Spatio-Temporal Analysis of Various Wildfire and Drought Indicators in Indonesia

Wildfires are well known as annual disasters in Indonesia. More than 3 million ha was burned in the last 5 years. During an extreme event such as in 2019, carbon emissions can cause smog disasters in neighboring countries such as Malaysia and Singapore. Though difficult to predict, many hotspots that appear can be used to indicate the emergence of large-scale wildfires. The objective of this research is to provide suggestions in terms of used variables when analyzing fire event indication (hotspot), fire event scale (burned area), and fire event impact (carbon emissions). This research provides a spatio-temporal analysis and dependency between drought (precipitation and its derivative variables) and fire indicators (hotspot, burned area, and carbon emission). This research provides the different characteristics of each indicator when used to find joint patterns of burned areas, hotspots, and carbon emissions. Overall, using potential evapotranspiration and precipitation to calculate climate water balance gives great results in all analysis. Precipitation anomalies give the best joint spatial pattern to describe wildfire events in the area with monsoonal rainfall. Meanwhile, precipitation gives better results by capturing more wildfire events in a temporal pattern, even on robust analysis.

Integrated graph measures reveal survival likelihood for buildings in wildfire events

Wildfire events have resulted in unprecedented social and economic losses worldwide in the last few years. Most studies on reducing wildfire risk to communities focused on modeling wildfire behavior in the wildland to aid in developing fuel reduction and fire suppression strategies. However, minimizing losses in communities and managing risk requires a holistic approach to understanding wildfire behavior that fully integrates the wildland’s characteristics and the built environment’s features. This complete integration is particularly critical for intermixed communities where the wildland and the built environment coalesce. Community-level wildfire behavior that captures the interaction between the wildland and the built environment, which is necessary for predicting structural damage, has not received sufficient attention. Predicting damage to the built environment is essential in understanding and developing fire mitigation strategies to make communities more resilient to wildfire events. In this study, we use integrated concepts from graph theory to establish a relative vulnerability metric capable of quantifying the survival likelihood of individual buildings within a wildfire-affected region. We test the framework by emulating the damage observed in the historic 2018 Camp Fire and the 2020 Glass Fire. We propose two formulations based on graph centralities to evaluate the vulnerability of buildings relative to each other. We then utilize the relative vulnerability values to determine the damage state of individual buildings. Based on a one-to-one comparison of the calculated and observed damages, the maximum predicted building survival accuracy for the two formulations ranged from 58 - 64 % for the historical wildfires tested. From the results, we observe that the modified random walk formulation can better identify nodes that lie at the extremes on the vulnerability scale. In contrast, the modified degree formulation provides better predictions for nodes with mid-range vulnerability values.

Wildfire effect on forest rainfall infiltration and runoff: a cellular automata-based simulation

A storm event-based simulation system is developed to reproduce the effects of wildfire on a predefined forest area's rainfall infiltration and runoff. The simulation system reproduces individual surface cell slope, infiltration capacity, and hydrophobicity. A cellular automaton represents space and time. The Horton equation reproduces infiltration capacity evolution. Different equation parameters account for precipitation intensity variations. Infiltration volume and runoff velocity are computed at the cell level. A Digital Elevation Model reproduces the topography. A real rainfall event is reproduced for a section of La Primavera Forest in Jalisco, Mexico. For a subwatershed within the area of interest, wildfire effects are shown on infiltration, overland flow and outlet discharge throughout the rainfall event. It is shown that rainfall infiltration for wildfire affected terrain is lower and that overland flow and outlet discharge is higher. Infiltration and runoff dynamics at a surface cell depend on storm profile, cell slope, cell soil texture, and overall topography. Water dynamics on the area of interest are shown with a movie effect. It is concluded that a cellular automaton-based model can reproduce infiltration and runoff for different soil texture, topographic and rain conditions. This simulation system is geared for an optimisation system to pinpoint the locations of a series of forest land remediation controls that or maximise infiltration or minimise runoff.

Wildfire Smoke Exposure During Pregnancy and Preterm Birth in California

Background/Aim Owing to climate change and fire suppression policy, wildfires in the Western United States are a significant source of air pollution that threatens to reverse decades of progress in air pollution reduction; effects of wildfires on preterm birth (PTB) are not well understood. We assessed associations between prenatal exposure to wildland fire (wildfire and prescribed fire) smoke and risk of PTB in California. Methods The population included all live singleton births in California, 2007-2015. PTB was defined as gestational age <37 weeks. We assigned wildland fire smoke exposure to geocoded maternal residence at birth with weekly average concentrations of particulate matter ≤2.5 microns attributable to fires from USEPA’s Community Multiscale Air Quality Model (fire PM2.5) and smoke frequencies (smoke days) from National Oceanic and Atmospheric Administration’s Hazard Mapping System. We used logistic regression to estimate odds ratios (OR) for PTB associated with exposures in the final 6 weeks of pregnancy and Cox proportional hazard models to estimate hazard ratios (HR) for PTB in relation to weekly exposures. Models adjusted for maternal age, education, race/ethnicity, season, medical insurance, and smoking. Results Our study included 3,342,267 births. A one-smoke day increase in any of the final 6 weeks of the pregnancy was associated with increased odds of PTB, ranging from OR=1.01 (95%CI:1.01-1.02) in the final week of pregnancy to OR=1.03 (95%CI:1.02-1.03) 5 weeks before birth. A 10µg/m3 increase in fire PM2.5 in the final 6 weeks was associated with ORs ~1.04 (95%CIs covered 1.02-1.06). In survival analyses, HR=1.01 (95%CI:1.01-1.02) for a one-day increase in smoke frequency and HR=1.03 (95%CI:1.02-1.04) for a 10µg/m3 increase in fire PM2.5. Conclusion Wildland fire smoke is modestly associated with PTB. Results can inform efforts to slow climate change, manage forests, and reduce wildfire smoke exposure to pregnant people. Keywords wildfire; pregnancy; preterm birth; climate; air pollution

Mapping the mechanistic evidence of wood smoke and wildfire studies in humans

Background and Aim Wood smoke is a complex mixture of gases, chemicals, and fine particles generated by wood-burning and wildfires. We are conducting a cancer hazard evaluation of wood smoke for possible listing in the U.S. Report on Carcinogens. The database of cancer epidemiology studies for exposure to wood smoke, but not wildfire, is adequate to conduct an evaluation. As mechanistic evidence may inform the overall hazard evaluation, especially for wildfires, we mapped the published evidence by biomarkers for the key characteristic of carcinogens (KCC), focusing here on studies in exposed humans. Methods We systematically searched three bibliographic databases for relevant biomarker studies on wildfire and wood smoke exposure. For selected studies reporting on the three most common KCCs (genotoxicity, oxidative stress, immune biomarkers), we extracted information including specific KCC biomarkers (e.g., mutations), results, study design, and population, and presented the data in an interactive evidence map. Results Wood smoke: Most human studies (26) found positive associations with KCCs, consistent with the >70 non-human studies (in vitro and in vivo). Inflammation, inflammatory cytokines, and lipid peroxidation were the most common KCCs in humans. The studies were primarily intervention or cross-sectional in populations cooking or heating with wood or randomized studies of controlled exposure. Wildfires: Human studies (15) were largely positive for immune biomarkers but inconsistent for genotoxicity and oxidative stress, whereas non-human studies (17) were generally positive for all endpoints. Most studies measured KCCs in firefighters (13) before or after exposure (e.g., work shift or natural wildfire event). Conclusions Wildfires are increasing in frequency and intensity due to climate change, and exposure to wood smoke remains a worldwide concern. This mechanistic evidence will help inform the cancer hazard evaluations of these exposures. Ongoing risk-of-bias evaluations may explain heterogeneity in human wildfire studies. Keywords Wood smoke, wildfires, biomarkers, exposed humans

Identification of smoke and sulfuric acid aerosol in SAGE III/ISS extinction spectra

Abstract. We developed a technique to classify the composition of enhanced aerosol layers as either smoke or sulfuric acid aerosol using extinction spectra from the Stratospheric Aerosol and Gas Experiment III instrument aboard the International Space Station (SAGE III/ISS). This method takes advantage of the different spectral properties of smoke and sulfuric acid aerosol, which is manifest in distinctly different spectral slopes in the SAGE III/ISS data. Herein we demonstrate the utility of this method and present an evaluation of its performance using four case-study events of two moderate volcanic eruptions (2018 Ambae eruption and 2019 Ulawun eruption, both of which released <0.5 Tg of SO2) and two large wildfire events (2017 Canadian pyroCb and 2020 Australian pyroCb). We provide corroborative data from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument to support these classifications. This method correctly classified smoke and sulfuric acid plumes in the case-study events >81 % and >99.5 % of the time, respectively. The application of this method to a large volcanic event (i.e., the 2019 Raikoke eruption; ≥1.5 Tg SO2) serves as an example of why this method is limited to small and moderate volcanic events as it incorrectly classified Raikoke's larger sulfuric acid particles as smoke. We evaluated the possibility of smoke being present in the stratosphere before and after the Raikoke eruption. While smoke was present during this time period it was insufficient to account for the magnitude of smoke classifications we observed. Therefore, while this method worked well for large-scale wildfire events and eruptions that inject less SO2, the size of the aerosol created by the Raikoke eruption was outside the applicable range of this method.

Interactive effects of wildfires, season and predator activity shape mule deer movements.

Wildfires are increasing in size, frequency and severity due to climate change and fire suppression, but the direct and indirect effects on wildlife remain largely unresolved. Fire removes forest canopy, which can improve forage for ungulates but also reduce snow interception, leading to a deeper snowpack and potentially increased vulnerability to predation in winter. If ungulates exhibit predator-mediated foraging, burns should generally be selected for in summer to access high-quality forage and avoided in winter to reduce predation risk in deep snow. Fires also typically increase the amount of deadfall and initiate the growth of dense understory vegetation, creating obstacles that may confer a hunting advantage to stalking predators and a disadvantage to coursing predators. To minimize risk, ungulates may therefore avoid burns when and where stalking predators are most active, and use burns when and where coursing predators are most active. We used telemetry data from GPS-collared mule deer (Odocoileus hemionus), cougars (Puma concolor) and wolves (Canis lupus) to develop step selection functions to examine how mule deer navigated species-specific predation risk across a landscape in northern Washington, USA, that has experienced substantial wildfire activity during the past several decades. We considered a diverse array of wildfire impacts, accounting for both the severity of the fire and time since the burn (1-35 years) in our analyses. We observed support for the predator mediating foraging hypothesis: mule deer generally selected for burned areas in summer and avoided burns in winter. In addition, deer increased use of burned areas when and where wolf activity was high and avoided burns when and where cougar use was high in winter, suggesting the hunting mode of resident predators mediated the seasonal response of deer to burns. Deer were not more likely to die by predation in burned than in unburned areas, indicating that they adequately manage fire-induced changes to predation risk. As fire activity increases with climate change, our findings indicate the impact on ungulates will depend on trade-offs between enhanced summer forage and functionally reduced winter range, mediated by characteristics of the predator community.

Experimental assessment of tundra fire impact on element export and storage in permafrost peatlands

Extensive studies have been performed on wildfire impact on terrestrial and aquatic ecosystems in the taiga biome, however consequences of wildfires in the tundra biome remain poorly understood. In such a biome, permafrost peatlands occupy a sizable territory in the Northern Hemisphere and present an extensive and highly vulnerable storage of organic carbon. Here we used an experimental approach to model the impact of ash produced from burning of main tundra organic constituents (i.e., moss, lichen and peat) on surrounding aquatic ecosystems. We studied the chemical composition of aqueous leachates produced during short-term (1 week) interaction of ash with distilled water and organic-rich lake water at 5 gsolid L−1 and 20 °C. The addition of ash enriched the fluid phase in major cations (i.e., Na, Ca, Mg), macro- (i.e., P, K, Si) and micronutrients (i.e., Mn, Fe, Co, Ni, Zn, Mo). This enrichment occurred over <2 days of experiment. Among 3 studied substrates, moss ash released the largest amount of macro- and micro-components into the aqueous solution. To place the obtained results in the environmental context of a peatbog watershed, we assume a fire return interval of 56 years and that the entire 0–10 cm of upper peat is subjected to fire impact. These mass balance calculations demonstrated that maximal possible delivery of elements from ash after soil burning to the hydrological network is negligibly small (<1–2 %) compared to the annual riverine export flux and element storage in thermokarst lakes. As such, even a 5–10 fold increase in tundra wildfire frequency may not sizably modify nutrient and metal fluxes and pools in the surrounding aquatic ecosystems. This result requires revisiting the current paradigm on the importance of wildfire impact on permafrost peatlands and calls a need for experimental work on other ecosystem compartments (litter, shrubs, frozen peat) which are subjected to fire events.

Significant Effective Radiative Forcing of Stratospheric Wildfire Smoke

AbstractThe radiative forcing (RF) of volcanic sulfate is well quantified. However, the RF of pyrocumulonimbus (pyroCb) smoke with absorbing carbonaceous aerosols has not been considered in climate assessment reports. With the Community Earth System Model, we studied two record‐breaking wildfire events, the 2017 Pacific Northwest Event (PNE) and the 2019–2020 Australian New Year event (ANY), that perturbed stratospheric chemistry and the earth's radiation budget. We calculated a global annual‐mean effective RF (ERF) of −0.04 ± 0.02 and −0.17 ± 0.02 W/m2 at the top of the atmosphere (TOA) for PNE and ANY, respectively. The complexity of longwave RF led to an uncertainty of about 50% in the ERF at the TOA among climate models. We found that modeled ERF from wildfire smoke was 70%–270% more negative than the ERF of mass‐equivalent sulfate aerosol, highlighting its important role in the climate radiative budget.