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The Canadian Forest Fire Danger Rating System (CFFDRS) and the National Forest Fire Danger Rating System (NFFDRS) were exercised under the Mediterranean forest type conditions of Crete Island, Greece in 2008–2009. The CFFDRS shows a high association between the assessed values of the duff moisture content on one hand and the Fine Fuel Moisture Code and the Duff Moisture Code on the other hand. During the designated fire seasons, there was an insignificant association between the Fire Weather Index and the wild forest fires which are contrary associated with wildfire occurrences. Meanwhile, the NFFDRS showed monitoring capabilities but with the insufficient prediction of the daily fire danger in the Mediterranean forests. During the tested forest fire seasons, there was an unstable association between the burnt area and the fire occurrences. Consequently, there was no significant correlation between the CFFDRS and the litter soil content. Although, CFFDRS has a higher prediction accuracy of moisture content of some shallow roots annual plants within the studied area. The findings of the current research emphasized that there is no single system that is adequate enough for both soil moisture content and the annuals moisture content simultaneously. [ABSTRACT FROM AUTHOR]

Microwaves have the advantage of penetrating vegetation and exhibit sensitivity to properties such as vegetation water content (VWC); yet, their potential utility in the fire domain is infrequently investigated. This study elucidates the different impacts of the microwave VWC index EDVI on fire radiative energy (FRE) across various biome types and the significant predictive power for high-severity fires (defined based on FRE) in mainland Southeast Asia. While EDVI exhibits lower predictive power for high severe fires compared to the commonly used fire weather indices (e.g., FWI), an enhancement is observed when these predictors are used in combination. Either by employing EDVI or fire weather indices, the predictability of fires is found to be highest over forests and lowest over croplands. Factors such as increasing human influence and fuel limitation in croplands are likely reducing the roles of VWC and weather on fires, contributing to the lower prediction skill of EDVI and fire weather. These results indicate the usefulness of microwave VWC index in fire studies. Although fire weather presents more considerable impacts on fires, the microwave VWC index seem to still provide some complementary information in fire danger assessment. [ABSTRACT FROM AUTHOR]

Rainforest, wet sclerophyll forest and eucalypt forest exist as Alternative Stable States moderated by fire. Eucalypt forest is flammable and subject to regular fire. Insights into the flammability of rainforest and wet sclerophyll forest are difficult to obtain because of the rarity of fire, particularly in sub-tropical and tropical environments. This study aimed to determine the relative flammability of rainforest and wet sclerophyll forest with a canopy of Lophostemon confertus in subtropical Australia. Fires in 2019, coinciding with extreme fire weather and following a long period of drought, burnt rainforest and wet sclerophyll forest in south-east Queensland. The weather record indicates these conditions recur about three to four times a century. Remapping of the vegetation overlaid with the fire-scar mapping, indicated that the 2019 fires burnt 23 % of rainforest, much of which was disturbed, but 60 % of wet sclerophyll forest suggesting greater flammability of the latter. This study revealed that above-ground biomass and litter fuel loads are more than twice as high in wet sclerophyll forest than rainforest. The litter of Lophostemon confertus, a Myrtaceae tree dominating the upper canopy, on average decomposes at less than half the rate of rainforest litter, contributing to the higher fuel loads and thus greater flammability of wet sclerophyll forest compared to rainforest. The Alternative Stable States of wet sclerophyll and rainforest are partly stabilised by the fire retardance of rainforest, the rarity of weather conditions suitable for fire in the subtropical environment and the higher fuel loads in wet sclerophyll forest that allow occasional fire. Wet sclerophyll forest requires rare fire events and the legacy of these fires over hundreds of years is evident in the multiple cohorts of 'giant' canopy trees. • During the 2019 bushfires in Australia, wet sclerophyll forest was much more flammable than pure rainforest. • High biomass of wet sclerophyll forest and slow decomposition of Myrtaceae leaf litter provides higher fuel loads compared to rainforest. • Wet sclerophyll forest ocassionally burns allowing for the persistence of rainforest species and the regeneration of giant Myrtaceae trees. • The rarity of weather conducive to burning and fuel dynamics rainforest and wet sclerophyll forest to exist as Alternative Stable States. [ABSTRACT FROM AUTHOR]

Fuel treatments are commonly applied to increase resilience to wildfire in dry and historically frequent-fire forests of western North America. The long-term effects of fuel treatments on forest structure, fuel profiles (amount and configuration of fuels), and potential wildfire behavior are not well known relative to short-term effects. Additionally, long-term treatment effects on the development of stand structure and fuel profiles have rarely been compared to the long-term effects of pre-treatment conditions, treatment intensity, and site productivity. In this study, we addressed these knowledge gaps by resurveying 204 permanent plots at the Northeastern Cascades site of the Fire and Fire Surrogates study 13–18 years ('long-term') after burn-only, thin-only, and thin plus burn treatments, and comparing results to pre-treatment conditions and un-treated controls. Methods included ordinations, generalized linear mixed models, and fire models. All treatments shifted long-term average stand structure toward lower tree density, basal area, and crown fire potential, with thin plus burn treatments showing the highest magnitude of effects for most variables. However, the direction and magnitude of trajectories among plots within treatment types were highly variable. Long-term responses of stand structure, fuel profiles, and modelled fire behavior were positively correlated with their pre-treatment values. Treatment intensity strongly affected long-term stand structure and canopy fuel loads. By ∼15 years post-treatment and under 80th percentile fire weather conditions, most plots in all treatments and un-treated controls failed to meet target thresholds for surface flame length, basal area mortality, and torching index, while most plots met thresholds for crowning index. However, live stand structure following wildfire simulated under 80th percentile fire weather conditions was characterized by lower stand density and a shift toward dominance by large-diameter and fire-resistant trees, suggesting that treated stands may be resilient to wildfires occurring under moderate weather. Our study suggests that understanding fuel treatment efficacy and longevity may be improved in future studies by incorporating fine-scale (i.e., plot-level) drivers of variability in stand structure, fuel profiles, and modelled fire behavior, and by using multiple methods of evaluating treatment effectiveness. Thin plus burn treatments and intensely applied burn-only and thin-only treatments can reduce basal area and potential for crown-fire for more than a decade. However, additional maintenance treatments may be needed by 15 years after initial treatment, to further reduce potential for severe surface fire and high tree mortality in subsequent wildfire. • Thin plus burn treatments showed the greatest long-term effects, in reducing basal area and potential for crown fire. • Treatments did not reduce potential for surface fire or wildfire-induced tree mortality in the long-term. • Pre-treatment values were positively correlated with long-term values for most response variables. • Greater treatment intensity was associated with long-term reductions in basal area, density, and potential for crown fire. • Fire models and threshold analyses suggested that maintenance may be needed 15 years following treatment, or earlier. [ABSTRACT FROM AUTHOR]

Wildfire is one of the most complex natural hazards. Its origin is a combination of anthropogenic factors, urban development and weather plus climate factors. In particular, weather and climate factors possess many spatiotemporal scales and various degrees of predictability. Due to the complex synergy of the human and natural factors behind the events, every wildfire is unique. However, there are indeed common meteorological and climate factors leading to the high fire risk before certain ignition mechanismfigures occur. From a scientific point of view, a better understanding of the meteorological and climate drivers of wildfire in every region would enable more effective seasonal to annual outlook of fire risk, and in the long term, better applications of climate projections to estimate future scenarios of wildfire. This review has performed a comparison study of two fire-prone regions: southeast Australia including Tasmania, and the Adriatic coast in Europe, especially events in Croatia. The former is well known as part of the ‘fire continent’, and major resources have been put into wildfire research and forecasting. The Adriatic coast is a region where some of the highest surface wind speeds, under strong topographic effect, have been recorded and, over the years, have coincided with wildfire ignitions. Similar synoptic background and dynamic origins of the meso-micro-scale meteorological conditions of these high wind events as well as the accompanied dryness have been identified between some of the events in the two regions. We have also reviewed how the researchers from these two regions have applied different weather indices and numerical models. The status of estimating fire potential under climate change for both regions has been evaluated. This review aims to promote a global network of information exchange to study the changing anthropogenic and natural factors we have to confront in order to mitigate and adapt the impacts and consequences from wildfire.

Context: Proximity of landcover elements to each other will enable or constrain fire spread. Assessments of potential fire propagation across landscapes typically involve empirical or simulation models that estimate probabilities based on complex interactions among biotic and abiotic controls. Objectives: We developed a metric of landscape fire exposure based solely on a grid cell's proximity to nearby hazardous fuel capable of transmitting fire to its location. To evaluate accuracy of this new metric, we asked: Do burned areas occur preferentially in locations with high exposure? Methods: We mapped exposure to hazardous fuels in Alberta, Canada using a neighbourhood analysis. Correspondence between exposure and 2331 fires that burned 2,606,387 ha following our 2007 assessment was evaluated and exposure changes between 2007 and 2019 were assessed. Results: In all eleven ecological units analysed, burned area surpluses occurred where exposure was ≥ 60% and corresponding deficits occurred where exposure was < 40%. In seven ecological units, the majority of burned areas had pre-fire exposure ≥ 80%. Between 2007 and 2019, land area with exposure ≥ 80% increased by almost a third. Conclusions: Exposure to hazardous fuels is easily quantified with a single thematic layer and aligns well with subsequent fires in Boreal, Foothills and Rocky Mountain natural regions. The resulting fire exposure metric is a numeric rating of the potential for fire transmission to a location given surrounding fuel composition and configuration, irrespective of weather or other fire controls. Exposure can be compared across geographic regions and time periods; and used in conjunction with other metrics of fire controls to inform the study of landscape fire. [ABSTRACT FROM AUTHOR]

Disastrous bushfires during the last months of 2019 and January 2020 affected Australia, raising the question to what extent the risk of these fires was exacerbated by anthropogenic climate change. To answer the question for southeastern Australia, where fires were particularly severe, affecting people and ecosystems, we use a physically based index of fire weather, the Fire Weather Index; long-term observations of heat and drought; and 11 large ensembles of state-of-the-art climate models. We find large trends in the Fire Weather Index in the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Atmospheric Reanalysis (ERA5) since 1979 and a smaller but significant increase by at least 30 % in the models. Therefore, we find that climate change has induced a higher weather-induced risk of such an extreme fire season. This trend is mainly driven by the increase of temperature extremes. In agreement with previous analyses we find that heat extremes have become more likely by at least a factor of 2 due to the long-term warming trend. However, current climate models overestimate variability and tend to underestimate the long-term trend in these extremes, so the true change in the likelihood of extreme heat could be larger, suggesting that the attribution of the increased fire weather risk is a conservative estimate. We do not find an attributable trend in either extreme annual drought or the driest month of the fire season, September–February. The observations, however, show a weak drying trend in the annual mean. For the 2019/20 season more than half of the July–December drought was driven by record excursions of the Indian Ocean Dipole and Southern Annular Mode, factors which are included in the analysis here. The study reveals the complexity of the 2019/20 bushfire event, with some but not all drivers showing an imprint of anthropogenic climate change. Finally, the study concludes with a qualitative review of various vulnerability and exposure factors that each play a role, along with the hazard in increasing or decreasing the overall impact of the bushfires. [ABSTRACT FROM AUTHOR]

Strong winds that accentuated a fire outbreak in the western United States in early September of 2020 resulted from an atmospheric wave train that spanned the Pacific Ocean. Days before the atmospheric waves developed in the United States, three western Pacific tropical cyclones (typhoons) underwent an extratropical transition over Korea within an unprecedentedly short span of 12 days. Using a climate diagnostic approach and historical forecast data, it was found that the amplitude of the atmospheric waves accompanying the western U.S. fire weather would not have been so profound if not for the influence of these typhoons. Together, the recurving typhoons provided a significant source of wave activity flux directed toward North America – amplifying the ridge over the U.S. west coast while deepening the trough in central Canada. This anomalous circulation produced the severe frontal system that caused extreme winds in western Oregon, Washington and California – rapidly spreading fire. Plain Language Summary: The weather pattern that contributed to rapidly spreading fires in Oregon in early September 2020 can be traced back to an unexpected source: Three typhoons in the western Pacific that ran into the Korean Peninsula within two weeks of each other. Together, Typhoon Bavi, Typhoon Maysak, and Typhoon Haishen each contained enough energy to perturb the jet stream – creating an atmospheric wave train that enhanced the hot, dry weather of the western United States. This study uses forecast models and weather observations to show that these typhoons amplified areas of high and low pressure in North America leading to the intense winds which rapidly spread fire in Oregon, Washington, and California. While the impacts of climate change on these events were not evaluated in this study, the implication is that the effect of weather extremes that are known to be exasperated by climate warming are not always limited to the region in which those extremes occur. Key points: Three western Pacific typhoons tracked through the Korean peninsula – with sequential landfall within a two‐week period of timeThe diabatic outflow from these typhoons amplified an atmospheric wave train – increasing the pressure gradient over the western U.S.The heightened pressure gradient resulted in strong winds, a key element in the rapid spread of fires in Oregon and California [ABSTRACT FROM AUTHOR]

We celebrate the 50th anniversary of the Canadian Journal of Forest Research by reflecting on the considerable progress accomplished in select areas of Canadian wildland fire science over the past half century. Specifically, we discuss key developments and contributions in the creation of the Canadian Forest Fire Danger Rating System; the relationships between wildland fire and weather, climate, and climate change; fire ecology; operational decision support; and wildland fire management. We also discuss the evolution of wildland fire management in Banff National Park as a case study. We conclude by discussing some possible directions in future Canadian wildland fire research including the further evaluation of fire severity measurements and effects; the efficacy of fuel management treatments; climate change effects and mitigation; further refinement of models pertaining to fire risk analysis, fire behaviour, and fire weather; and the integration of forest management and ecological restoration with wildland fire risk reduction. Throughout the paper, we reference many contributions published in the Canadian Journal of Forest Research, which has been at the forefront of international wildland fire science. [ABSTRACT FROM AUTHOR]

Forest fire hazard is a major problem in the Mediterranean region of Turkey and has a significant effect on both the climate system and ecosystems. During the last century, many forest fires accounted for the majority of the Mediterranean region in Turkey. Vector singular spectrum analysis (V-SSA) and vector multivariate singular spectrum analysis (V-MSSA) are relatively novel but powerful time series analysis techniques. The present study addresses how to forecast burned forest area (BFA) by V-SSA. One of the most important factors affecting forest fires is weather conditions. The prediction of BFA is therefore also obtained by V-MSSA using meteorological covariates (i.e., relative humidity (RH), temperature (T) and wind speed (WS). In the study, forest fire data records covering the years 2005–2019 were collected and analyzed. To gain forecast accuracy, the years 2017–2019 were used as testing data, and forecast values for 1, 3, 6, 12, 24 and 36 months were obtained. Then, V-SSA and V-MSSA models were compared via the root mean square errors (RMSEs) to reach the best model explaining BFA. Our results indicated that the RMSEs of the eight models were low and close to each other. Further, forecasts for the months of the years 2020–2022 were obtained and compared with actual BFA values by means of the RMSEs. According to RMSEs, the best forecasts are obtained using the V-MSSA model with meteorological covariates BFA, WS and T. [ABSTRACT FROM AUTHOR]

Widespread fire activity taxes suppression resources and can compound wildfire hazards. We examine the geographic synchronicity of fire danger across western United States forests as a proxy for the strain on fire suppression resource availability. Interannual variability in the number of days with synchronous fire danger, defined as fire weather indices exceeding the local 90th percentile across ≥40% of forested land, was strongly correlated (r = 0.85) with the number of days with high strain on national fire management resources. A 25‐day increase in the annual number of days with synchronous fire danger was observed during 1979–2020. Climate projections show a doubling of such days by 2051–2080. Such changes will escalate the likelihood of years with extended periods of synchronous fire danger that have historically strained suppression efforts and contributed to additional burned area, therein requiring additional management strategies for coping with anticipated surges in fire suppression demands. Plain Language Summary: The amount of area burned per year in forests across the western United States has been increasing over the past half‐century alongside warmer and drier weather conditions in the summer months of the western United States, called the "fire season." These conditions lead to a number of impacts on ecosystems and society with mounting challenges for fire suppression. The occurrence of widespread fire danger and fire activity during active fire seasons has overwhelmed fire suppression resource capacity, limiting the effectiveness of managing fires and potentially increasing fire impacts. We find a strong link between fire danger days across western US forests and the number of days with high strain on national fire suppression resources. We show a 25‐day increase in the annual number of days of regionally widespread connected fire danger‐fire resource strain over the past 4 decades, and a doubling of such days by the mid‐21st century. These findings suggest that, if fuel availability, ignition patterns, and land management approaches do not substantially change over time, climate change may continue to overburden fire management efforts across the region, requiring careful strategy when fire resources are strained in future dangerous, prolonged fire seasons. Key Points: Synchronous fire danger days across western US forests are interannually correlated with strain on national fire suppression resourcesA 25‐day increase in the annual number of days with synchronous fire danger was observed during 1979–2020A doubling in the number of synchronous fire danger days is projected by 2051–2080 [ABSTRACT FROM AUTHOR]

Attribution studies have identified a robust anthropogenic fingerprint in increased 21st century wildfire risk. However, the risks associated with individual aspects of anthropogenic aerosol and greenhouse gases (GHG) emissions, biomass burning and land use/land cover change remain unknown. Here, we use new climate model large ensembles isolating these influences to show that GHG-driven increases in extreme fire weather conditions have been balanced by aerosol-driven cooling throughout the 20th century. This compensation is projected to disappear due to future reductions in aerosol emissions, causing unprecedented increases in extreme fire weather risk in the 21st century as GHGs continue to rise. Changes to temperature and relative humidity drive the largest shifts in extreme fire weather conditions; this is particularly apparent over the Amazon, where GHGs cause a seven-fold increase by 2080. Our results allow increased understanding of the interacting roles of anthropogenic stressors in altering the regional expression of future wildfire risk. Human emissions are thought to have caused an increase in wildfire risk, but how different emission sources contribute is less well known. Here, the authors show that the increase due to greenhouse gas emissions was balanced by aerosol-driven cooling, an effect that is projected to disappear during the 21st century. [ABSTRACT FROM AUTHOR]

High‐resolution regional climate simulations were conducted for the past 30 years (1987–2016), focusing on the Euro‐Mediterranean region. The numerical simulations were used for computing the Canadian Fire Weather Index, for deriving the climatology of fire weather in the study area and investigating the presence of long‐term trends, with particular emphasis on extremes during the May to September period. Results suggest that the Euro‐Mediterranean fire weather follows a zonal pattern, characterized by adverse conditions occurring most frequently in the southern parts. Air temperature and relative humidity are the key drivers of fire weather in the study area, with precipitation and wind exerting less influence. Based on the conducted spatial trend analysis, extreme fire weather conditions have become more prevalent in the Iberian Peninsula and eastern Balkans, whereas declining trends occur in the Southeast Mediterranean basin. For both cases, the trends in fire weather extremes appear to coincide with trends in the input meteorological variables. Overall, the results of this study provide a new insight on the recent climatology and trends of fire weather in the Euro‐Mediterranean. Our dataset is publicly available on the Zenodo platform (DOI: 10.5281/zenodo.3713531). [ABSTRACT FROM AUTHOR]

Fire incidence has been linked to multiple factors such as climate conditions, population density, agriculture, and lightning. Recently, fire frequency and severity have induced health problems and contributed to increase atmospheric greenhouse gases. Based on atmospheric susceptibility to fire, this study evaluates the use of a Potential Fire Index (PFIv2) to identify regions prone to fire development, as demonstrated by the satellite detected‐fire in the 2001–2016 interval. It is demonstrated that PFIv2 delivers an efficiency by up to 80% in matching the observed fires from Terra/MODIS satellite. The PFIv2 is also able to reproduce more accurately areas with fire activity with respect to its previous version, the PFI. This better performance is linked to the implementation of parameterization of water pressure deficit and atmospheric stability in the lower troposphere, and a new term to represent the effect of surface temperatures, particularly in mid‐latitudes and extra‐Tropics. To evaluate the performance of the PFIv2 in more details, its comparison to MODIS burned areas demonstrated correlations values higher than 0.6 over the most susceptible regions such as Africa and South America, slightly lower correlation is found where fire does not primary follows the climate annual cycle, and is dominated by high frequency events. These findings indicate that the PFIv2 can be an important tool for decision makers in predicting the potential for vegetation fires development and fire danger. [ABSTRACT FROM AUTHOR]

With rising temperatures and decreasing soil water, the frequency of vegetation fires is increasing globally. We analyzed the impact of climate change on the frequency of vegetation fires that required intervention by the Czech Fire Rescue Service in the Czech Republic between 1971 and 2015. We analyzed spatial patterns across administrative regions and evaluated the role of climate and other contributing factors that could explain spatiotemporal shifts during the study period. Our study has shown that the frequency of vegetation fires has increased most in the warmest and driest areas of the Czech Republic countryside. The increase between 1991 and 2015 is about 70% in comparison with the 1971–1990 period. In all administrative regions, a statistically significant relationship of the frequency of vegetation fires and weather conditions has been demonstrated. In all regions of the study area, extreme occurrences of vegetation fires were due to a combination of drought and heat waves. We conclude that population growth at the wildland-urban interface causes a greater frequency of vegetation fires. However, the main reason for the statistically significant increase in the frequency of vegetation fires is the ongoing climate change, manifested by an increase in values of the Fire Danger Index and heat wave occurrence. [ABSTRACT FROM AUTHOR]

"Megafires" are of scientific interest and concern for fire management, public safety planning, and smoke-related public health management. There is a need to predict them on time scales from days to decades. Understanding is limited, however, of the role of daily weather in determining their extreme size. This study examines differences in the daily weather during these and other smaller fires, and in the two sets of fires' responses to daily weather and antecedent atmospheric dryness. Twenty fires of unusual size (over 36 400 ha), were each paired with a nearby large fire (10 100–30 300 ha). Antecedent dryness and daily near-surface weather were compared for each set of fires. Growth response to daily weather was also examined for differences between the two sets of fires. Antecedent dryness measured as the evaporative demand drought index was greater for most of the fires of unusual size than it was for smaller fires. There were small differences in daily weather, with those differences indicating weather less conducive to fire growth for the unusually large fires than the smaller fires. Growth response was similar for the two sets of fires when weather properties were between 40th and 60th percentiles for each fire pair, but the unusually large fires' growth was observably greater than the smaller fires' growth for weather properties between the 80th to 100th percentiles. Response differences were greatest for wind speed, and for the Fosberg fire weather index and variants of the hot-dry-windy index, which combine wind speed with atmospheric moisture. Significance Statement: Some wildfires grow substantially larger, and more rapidly, than the vast majority of others. This growth makes them more difficult to manage and increases their potential to cause injury, death, or property damage. We looked at how the growth of these fires relates to daily weather, either with more fire-conducive weather or with a different growth response to the weather. We found evidence suggesting that it is the growth response, not the weather itself, that differs. Results consistently pointed to high wind events as being related to disproportionate fire growth. Our results could help improve planning for these types of events both in the short term and in terms of climate impacts on fire. [ABSTRACT FROM AUTHOR]

We currently explore avenues towards improved modelling with covariate shifts in the tails of the covariate distribution. It astutely incorporates meteorological and topographic risk drivers and accounts for other, unknown factors of spatial variability, making it reliable for short-term prediction and long-term projection under climate change. We congratulate the authors for their carefully constructed spatial model of risk occurrences caused by pluvial flooding. [Extracted from the article]

This study uses an interdisciplinary approach to investigate variability in fire weather, fire activity and fire management decision spaces in western Canada from three separate perspectives. We used time series analysis to identify periodic and quasi-periodic components of fire weather measures at second, hourly, daily, yearly, and multi-decadal resolution in 3 ecozones. Examples of relationships between scales of fire weather and fire activity were taken from the literature. Through interviews with and observation of Canadian wildland fire management agencies we identified 20 typical decision problems which we mapped to 16 spatio-temporally cohesive decision spaces extending from incident to national levels and immediate to multi-decadal time spans. To connect these domains, we propose that space time cascades of atmospheric kinetic energy are reflected in an inverse cascade of wildfire activity, and shape the spatio-temporal dimensions of decision spaces and the pace of fire management decisions.

Cold fronts are typically associated with cooling, drying and a strengthening wind that shifts to have a northerly component. Cold front effects at a particular point, however, are dependent upon pre-existing air mass characteristics. Here, we examine 634 passages of synoptic-scale cold fronts in northeastern Minnesota from 2010 to 2018. While these fronts are associated with the expected effects in some areas, they are often associated with warming and enhanced drying in the region directly influenced by an air mass from Lake Superior (coastal sites). Coastal sites experience warming during more than half of cold frontal passages, in contrast to proximate inland sites out of the influence of the lake. This warming, combined with a removal of the moist lake air mass, often leads to a sharp post-front decrease in relative humidity. These relatively unusual local effects indicate a need to carefully consider characteristics of the lake air mass and likely changes during cold frontal passage when forecasting regional temperature and fire weather conditions.

The 2021 fire season in Greece was the worst of the past 13 years, resulting in more than 130,000 ha of burnt area, with about 70% consumed by five wildfires that ignited and spread in early August. Common to these wildfires was the occurrence of violent pyroconvection. This work presents a meteorological analysis of this outbreak of extreme pyroconvective wildfires. Our analysis shows that dry and warm antecedent weather preconditioned fuels in the fire-affected areas, creating a fire environment that alone could effectively support intense wildfire activity. Analysis of surface conditions revealed that the ignition and the most active spread of all wildfires coincided with the most adverse fire weather since the beginning of the fire season. Further, the atmospheric environment was conducive to violent pyroconvection, as atmospheric instability gradually increased amid the breakdown of an upper-air ridge ahead of an approaching long-wave trough. In summary, we highlight that the severity and extent of the 2021 Greek wildfires were not surprising considering the fire weather potential for the period when they ignited. Continuous monitoring of the large- and local-scale conditions that promote extreme fire behavior is imperative for improving Greece’s capacity for managing extreme wildfires.

Deforestation exacerbates climate change through greenhouse gas emissions, but other climatic alterations linked to the local biophysical changes from deforestation remain poorly understood. Here, we assess the impact of tropical deforestation on fire weather risk—defined as the climate conditions conducive to wildfires—using high-resolution convection-permitting climate simulations. We consider two land cover scenarios for the island of Borneo: land cover in 1980 ( forest scenario ) and land cover in 2050 ( deforestation scenario ) to force a convection-permitting climate model, using boundary conditions from ERA-Interim reanalysis for the 2002–2016 period. Our findings revealed significant alterations in post-deforestation fire precursors such as increased temperature, wind speed and potential evapotranspiration and decreased humidity, cloud cover and precipitation. As a result, fire weather events that would occur once a year in the forested scenario, are likely to occur four times a year following deforestation. Likewise, for extreme conditions, such as those occurring on longer time-horizons than 20 years, the magnitude of extreme fire weather is likely to double following deforestation. These increases in extreme fire weather conditions demonstrate the key role of tropical forests in regulating regional climate processes, including reduced fire weather risk.

Massive wildfires and extreme fire behavior are becoming more frequent across the western United States, creating a need to better understand how megafire behavior will evolve in our warming world. Here, the fire spread model Prometheus is used to simulate the initial explosive growth of the 2020 August Complex, which occurred in northern California (CA) mixed conifer forests. High temperatures, low relative humidity, and daytime southerly winds were all highly correlated with extreme rates of modeled spread. Fine fuels reached very dry levels, which accelerated simulation growth and heightened fire heat release (HR). Model sensitivity tests indicate that fire growth and HR are most sensitive to aridity and fuel moisture content. Despite the impressive early observed growth of the fire, shifting the simulation ignition to a very dry September 2020 heatwave predicted a >50% increase in growth and HR, as well as increased nighttime fire activity. Detailed model analyses of how extreme fire behavior develops can help fire personnel prepare for problematic ignitions.

Biomass fires in Indonesia emit high levels of greenhouse gases and particulate matter, key contributors to global climate change and poor air quality in south-east Asia. In order to better understand the drivers of biomass fires across Indonesia over multiple years, we examined the distribution and probability of fires in Sumatra, Kalimantan (Indonesian Borneo) and Papua (western New Guinea) over four entire calendar years (2002, 2005, 2011 and 2015). The 4 years of data represent years with El Niño and La Niña conditions and high levels of data availability in the study region. Generalised linear mixed-effects models and zero-inflated negative binomial models were used to relate fire hotspots and a range of spatial predictor data. Geographic differences in occurrences of fire hotspots were evident. Fire probability was greatest in mixed-production agriculture lands and in deeper, degraded peatlands, suggesting anthropogenic activities were strong determinants of burning. Drought conditions in El Niño years were also significant. The results demonstrate the importance of prioritising areas of high fire probability, based on land use and other predisposing conditions, in effective fire management planning. We modelled the relationship between fire occurrence and different spatial factors across Indonesia. We found that fires were associated with human-disturbed land covers, suggesting that most fires in Indonesia originated from human activities. Fires were also associated with drier, hotter weather ranking higher on the fire weather index. [ABSTRACT FROM AUTHOR]

The Northern California Camp Fire that took place in November 2018 was one of the most damaging environmental events in California history. Here, we analyze ground-based station observations of airborne particulate matter that has a diameter <2.5 µm (PM 2.5) across Northern California and conduct numerical simulations of the Camp Fire using the Weather Research and Forecasting model online coupled with chemistry (WRF-Chem). Simulations are evaluated against ground-based observations of PM 2.5 , black carbon, and meteorology, as well as satellite measurements, such as Tropospheric Monitoring Instrument (TROPOMI) aerosol layer height and aerosol index. The Camp Fire led to an increase in Bay Area PM 2.5 to over 50 µgm-3 for nearly 2 weeks, with localized peaks exceeding 300 µgm-3. Using the Visible Infrared Imaging Radiometer Suite (VIIRS) high-resolution fire detection products, the simulations reproduce the magnitude and evolution of surface PM 2.5 concentrations, especially downwind of the wildfire. The overall spatial patterns of simulated aerosol plumes and their heights are comparable with the latest satellite products from TROPOMI. WRF-Chem sensitivity simulations are carried out to analyze uncertainties that arise from fire emissions, meteorological conditions, feedback of aerosol radiative effects on meteorology, and various physical parameterizations, including the planetary boundary layer model and the plume rise model. Downwind PM 2.5 concentrations are sensitive to both flaming and smoldering emissions over the fire, so the uncertainty in the satellite-derived fire emission products can directly affect the air pollution simulations downwind. Our analysis also shows the importance of land surface and boundary layer parameterization in the fire simulation, which can result in large variations in magnitude and trend of surface PM 2.5. Inclusion of aerosol radiative feedback moderately improves PM 2.5 simulations, especially over the most polluted days. Results of this study can assist in the development of data assimilation systems as well as air quality forecasting of health exposures and economic impact studies. [ABSTRACT FROM AUTHOR]

Boreal wildfires are increasing in intensity, extent, and frequency, potentially intensifying carbon emissions and transitioning the region from a globally significant carbon sink to a source. The productive southern boreal forests of central Canada already experience relatively high frequencies of fire, and as such may serve as an analog of future carbon dynamics for more northern forests. Fire–carbon dynamics in southern boreal systems are relatively understudied, with limited investigation into the drivers of pre‐fire carbon stocks or subsequent combustion. As part of NASA's Arctic‐Boreal Vulnerability Experiment, we sampled 79 stands (47 burned, 32 unburned) throughout central Saskatchewan to characterize above‐ and belowground carbon stocks and combustion rates in relation to historical land use, vegetation characteristics, and geophysical attributes. We found southern boreal forests emitted an average of 3.3 ± 1.1 kg C/m2 from field sites. The emissions from southern boreal stands varied as a function of stand age, fire weather conditions, ecozone, and soil moisture class. Sites affected by historical timber harvesting had greater combustion rates due to faster carbon stock recovery rates than sites recovering from wildfire events, indicating that different boreal forest land use practices can generate divergent carbon legacy effects. We estimate the 2015 fire season in Saskatchewan emitted a total of 36.3 ± 15.0 Tg C, emphasizing the importance of southern boreal fires for regional carbon budgets. Using the southern boreal as an analog, the northern boreal may undergo fundamental shifts in forest structure and carbon dynamics, becoming dominated by stands <70 years old that hold 2–7 kg C/m2 less than current mature northern boreal stands. Our latitudinal approach reinforces previous studies showing that northern boreal stands are at a high risk of holding less carbon under changing disturbance conditions. [ABSTRACT FROM AUTHOR]

Background: Globally, and in the Cape Floristic Region of South Africa, extreme fires have become more common in recent years. Such fires pose societal and ecological threats and have inter alia been attributed to climate change and modification of fuels due to alien plant invasions. Understanding the flammability of different types of indigenous and invasive alien vegetation is essential to develop fire risk prevention and mitigation strategies. We assessed the flammability of 30 species of indigenous and invasive alien plants commonly occurring in coastal fynbos and thicket shrublands in relation to varying fire weather conditions. Methods: Fresh plant shoots were sampled and burnt experimentally across diverse fire weather conditions to measure flammability in relation to fire weather conditions, live fuel moisture, fuel load and vegetation grouping (fynbos, thicket and invasive alien plants). Flammability measures considered were: burn intensity, completeness of burn, time-to-ignition, and the likelihood of spontaneous ignition. We also investigated whether the drying of plant shoots (simulating drought conditions) differentially affected the flammability of vegetation groups. Results: Fire weather conditions enhanced all measures of flammability, whereas live fuel moisture reduced burn intensity and completeness of burn. Live fuel moisture was not significantly correlated with fire weather, suggesting that the mechanism through which fire weather enhances flammability is not live fuel moisture. It furthermore implies that the importance of live fuel moisture for flammability of evergreen shrublands rests on inter-specific and inter-vegetation type differences in fuel moisture, rather than short-term intra-specific fluctuation in live fuel moisture in response to weather conditions. Fuel load significantly increased burn intensity, while reducing ignitability. Although fire weather, live fuel moisture, and fuel load had significant effects on flammability measures, vegetation and species differences accounted for most of the variation. Flammability was generally highest in invasive alien plants, intermediate in fynbos, and lowest in thicket. Fynbos ignited rapidly and burnt completely, whereas thicket was slow to ignite and burnt incompletely. Invasive alien plants were slow to ignite, but burnt with the highest intensity, potentially due to volatile organic composition. The drying of samples resulted in increases in all measures of flammability that were comparable among vegetation groups. Flammability, and by implication fire risk, should thus not increase disproportionately in one vegetation group compared to another under drought conditions--unless the production of dead fuels is disproportionate among vegetation groups. Thus, we suggest that the dead:live fuel ratio is a potentially useful indicator of flammability of evergreen shrublands and that proxies for this ratio need to be investigated for incorporation into fire danger indices. [ABSTRACT FROM AUTHOR]

An important aspect of predicting future wildland fire risk is estimating fire weather—weather conducive to the ignition and propagation of fire—under realistic climate change scenarios. Because the majority of area burned occurs on a few days of extreme fire weather, this task should be able to resolve fire weather extremes. In this paper, we present a statistical downscaling procedure based on distribution based scaling (DBS) to bias correct the Fire Weather Index (FWI), part of the Canadian Forest Fire Danger Rating System, as calculated from modeled climate data. Our study area is western Canada (British Columbia and Alberta) and we consider both an historical control period (1990–2000) and three future time periods (2020–2030, 2050–2060, and 2080–2090). The historical data used to calibrate the DBS procedure comprises weather station data and weather from the North American Regional Reanalysis (NARR), whereas the future climate projections are the output of three regional climate models, corresponding to different model parameterizations and downscaled from the NCAR Community Earth System Model under the RCP 8.5 scenario. By fitting a truncated Weibull distribution to observed and modeled FWI values, our method is able to reproduce historical extremes in fire weather indices as determined by the distribution of annual potential spread days, which are defined as days with FWI values greater than 19. Moreover, by calibrating the DBS procedure with gridded reanalysis data as well as station observations, we are able to project future spread day distributions over the entire study area. The results of this study show the DBS procedure leads to a greater number of projected annual spread days at most locations compared with estimates using the uncorrected model output, and that all three RCM models show positive increases in potential annual spread days for the 2050–2060 and 2080–2090 time periods. [ABSTRACT FROM AUTHOR]

Fire management agencies use fire behaviour simulation tools to predict the potential spread of a fire in both risk planning and operationally during wildfires. These models are generally based on underlying empirical or quasi-empirical relations and rarely are uncertainties considered. Little attention has been given to the quality of the input data used during operational fire predictions. We examined the extent to which error in weather forecasts can affect fire simulation results. The study was conducted using data representing the State of Victoria in south-eastern Australia, including grassland and forest conditions. Two fire simulator software packages were used to compare fire growth under observed and forecast weather. We found that error in the weather forecast data significantly altered the predicted size and location of fires. Large errors in wind speed and temperature resulted in an overprediction of fire size, whereas large errors in wind direction resulted in an increased spatial error in the fire's location. As the fire weather intensified, fire predictions using forecast weather under predicted fire size, potentially resulting in greater risks to the community. These results highlight the importance of on-ground intelligence during wildfires and the use of ensembles to improve operational fire predictions. Fire simulators inform critical decisions for communities during wildfires. The sensitivity of these models to input data uncertainty is unknown. Fire area is most sensitive to error in temperature and wind speed, whereas location is most sensitive to error in wind direction. On-ground intelligence is vital for accurate fire predictions. [ABSTRACT FROM AUTHOR]

Large wildfire outbreaks in Alaska are common from June to August. The Canadian Forest Fire Danger Rating System (CFFDRS) is used operationally by Alaskan fire managers to produce statewide fire weather outlooks and forecast guidance near active wildfires. The CFFDRS estimates of fire potential and behavior rely heavily on meteorological observations (precipitation, temperature, wind speed, and relative humidity) from the relatively small number of in situ stations across Alaska with precipitation being the most critical parameter. To improve the spatial coverage of precipitation estimates across Alaska for fire weather applications, a multisatellite precipitation algorithm was evaluated during six fire seasons (1 June– 31 August 2014–19). Near-real-time daily precipitation estimates from the Integrated Multisatellite Retrievals for the Global Precipitation Mission (IMERG) algorithm were verified using 322 in situ stations across four Alaskan regions. For each region, empirical cumulative distributions of daily precipitation were obtained from station observations during each summer, and compared to corresponding distributions of interpolated values from IMERG grid points (0.1o x 0.1o grid). The cumulative distributions obtained from IMERG exhibited wet biases relative to the observed distributions for all regions, precipitation amount ranges, and summers. A bias correction approach using regional quantile mapping was developed to mitigate for the IMERG wet bias. The bias-adjusted IMERG daily precipitation estimates were then evaluated and found to produce improved gridded IMERG precipitation estimates. This approach may help to improve situational awareness of wildfire potential across Alaska and be appropriate for other high latitude regions where there are sufficient in situ precipitation observations to help correct the IMERG precipitation estimates. [ABSTRACT FROM AUTHOR]

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In 2009, new guidance for wildland fire management in the United States expanded the range of strategic options for managers working to reduce the threat of high-severity wildland fire, improve forest health and respond to a changing climate. Markedly, the new guidance provided greater flexibility to manage wildland fires to meet multiple resource objectives. We use Incident Status Summary reports to understand how wildland fire management strategies have differed across the western US in recent years and how management has changed since the 2009 Guidance for Implementation of Federal Wildland Fire Management Policy. When controlling for confounding variation, we found the 2009 Policy Guidance along with other concurrent advances in fire management motivated an estimated 27 to 73% increase in the number of fires managed with expanded strategic options, with only limited evidence of an increase in size or annual area burned. Fire weather captured a manager's intent and allocation of fire management resources relative to burning conditions, where a manager's desire and ability to suppress is either complemented by fire weather, at odds with fire weather, or put aside due to other priorities. We highlight opportunities to expand the use of strategic options in fire-adapted forests to improve fuel heterogeneity. In 2009, new federal guidance in the United States expanded options available to wildland fire managers. We explored this guidance in a context informed by concurrent weather and resource conditions, finding it helped expand the use of strategic responses beyond suppression. We also found a manager's desire and ability to suppress is either complemented by fire weather, at odds with fire weather, or put aside due to other priorities. We highlight opportunities to improve fuel heterogeneity in fire-adapted forests. [ABSTRACT FROM AUTHOR]

Variations in global patterns of burning and fire regimes are relatively well measured, however, the degree of influence of the complex suite of biophysical and human drivers of fire remains controversial and incompletely understood. Such an understanding is required in order to support current fire management and to predict the future trajectory of global fire patterns in response to changes in these determinants. In this study we explore and compare the effects of four fundamental controls on fire, namely the production of biomass, its drying, the influence of weather on the spread of fire and sources of ignition. Our study area is southern Australia, where fire is currently limited by either fuel production or fuel dryness. As in most fire-prone environments, the majority of annual burned area is due to a relatively small number of large fires. We train and test an Artificial Neural Network’s ability to predict spatial patterns in the probability of large fires (>1,250 ha) in forests and grasslands as a function of proxies of the four major controls on fire activity. Fuel load is represented by predicted forested biomass and remotely sensed grass biomass, drying is represented by fraction of the time monthly potential evapotranspiration exceeds precipitation, weather is represented by the frequency of severe fire weather conditions and ignitions are represented by the average annual density of reported ignitions. The response of fire to these drivers is often non-linear. Our results suggest that fuel management will have limited capacity to alter future fire occurrence unless it yields landscape-scale changes in fuel amount, and that shifts between, rather than within, vegetation community types may be more important. We also find that increased frequency of severe fire weather could increase the likelihood of large fires in forests but decrease it in grasslands. These results have the potential to support long-term strategic planning and risk assessment by fire management agencies.

A large-scale wildland fire occurred in Sakha in 2021. The results of fire analysis showed that the total number of hotspots in 2021 exceeded 267,000. This is about 5.8 times the average number of fires over the last 19 years since 2002. The largest daily number of hotspots in 2021 was 16,226, detected on 2 August. On 7 August, about half of the daily hotspots (52.6% = 8175/15,537 × 100) were detected in a highest fire density area (HFA, 62.5–65° N, 125–130° E) near Yakutsk under strong southeasterly wind (wind velocity about 12 m/s (43 km/h)). The results of weather analysis using various weather maps are as follows: The large meandering westerlies due to stagnant low-pressure systems in the Barents Sea brought high-pressure systems and warm air masses from the south to high latitudes, creating warm, dry conditions that are favorable conditions for fire. In addition to these, strong southeasterly winds at lower air levels blew which were related to the development of high-pressure systems in the Arctic Ocean. The HFA was located in the strong wind region (>8 m/s) of the v-wind map. The record-breaking Sakha fire season of 2021 is an example of extreme phenomena wrought by rapid climate change.