Michael D. Flannigan

The Canadian Fire Weather Index System (CFWIS) is widely used to characterize fire weather conditions and support wildfire risk assessments in real time as well as in historical trend analysis. To extend its application to future climate scenarios, we generated a daily CFWIS dataset for the 2050 s (2041–2070) and 2080 s (2071–2100) across Canada and the United States at 0.25° spatial resolution. The dataset is based on four CMIP6 global climate models (CanESM5, EC-Earth3, GFDL-ESM4, and UKESM1) and multiple Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5). Daily meteorological inputs were generated by applying monthly CMIP6 climate change factors to ERA5 reanalysis data (1991–2020). This approach preserves the daily variability and temporal sequencing of the ERA5 baseline while incorporating projected changes in mean climate conditions. Compared with raw daily GCM data, ERA5-derived inputs more closely reproduce observed meteorological distributions and produce substantially more realistic CFWIS component distributions. The dataset provides internally consistent daily fire-weather sequences suitable for comparative and scenario-based analyses across Canada and the United States.

Carbon emissions from disturbances in the Arctic-Boreal Zone (ABZ) are not adequately included in global carbon budgets due to insufficient measurements and model representation. Due to this data gap, we conducted an expert assessment to examine the potential trajectories of multiple disturbance types in the ABZ and their impacts on net carbon fluxes over the next one to three centuries. Across five disturbance categories – anthropogenic (e.g., oil and gas infrastructure), biotic, fire, abrupt permafrost thaw, and weather – experts agreed that the extent, frequency, range, and severity of disturbances will increase for at least the next century. Taken together, our assessment suggests that ABZ disturbances could result in 154–417 TgC yr ^− 1 (median expert estimates) greater net carbon emissions by 2100 relative to 2000–2020 for three climate change mitigation scenarios – global mean temperature increase held below (1) 1.5°C by 2100, (2) 2°C by 2100, and (3) Representative Concentration Pathway (RCP) 8.5 (~ 2.6–4.8°C by 2100 with rising temperatures beyond that). Critically, the experts agreed these impacts will persist long after global net zero anthropogenic emissions are reached, causing continued carbon emissions that are currently unaccounted for. Key research priorities for reducing uncertainty in these estimates were 1) improved spatio-temporal monitoring of ABZ disturbances to quantify their extent and distribution, 2) increased measurements of ecosystem carbon fluxes during and following disturbance events, and 3) incorporation of disturbance processes into models.

Background: Lightning-caused ignitions account for most annual area burned in Canada, and recent extreme fire seasons highlight the need to better understand atmospheric conditions that generate synchronous lightning-fire outbreaks. Aims: We quantified lightning-caused ignition clusters (LCICs) across Canada from 1980–2023, examining their spatiotemporal characteristics and associated weather patterns in eastern and western Canada. Methods: Using lightning-caused ignition records from the Canadian National Fire Database, we identified same-day LCICs with density-based spatial clustering. We computed anomalies in ERA5-derived synoptic variables and Canadian Forest Fire Danger Rating System (CFFDRS) fire weather indices on LCIC ignition dates and classified patterns using k-means clustering of 500-hPa geopotential height anomalies (Z500). Key results: We identified 2407–2692 LCICs, representing 55–64% of lightning-caused ignitions. Composite analyses revealed predominantly positive Z500, 850-hPa temperature, and fire weather anomalies over LCIC centroids, with stronger anomalies in eastern Canada. Most LCICs occurred in the Boreal Shield, Montane Cordillera and Boreal Plains ecozones, with regional contrasts in LCIC size, area burned and seasonality. Conclusions: LCICs are widespread and associated with distinct synoptic regimes and elevated fire weather severity, particularly in eastern Canada. Implications: Our results provide additional information to support wildfire prediction, preparedness and proactive resource positioning.

Wildfire behaviour is becoming increasingly volatile, expressed through more frequent and pronounced episodes of anomalously intense fire activity. Conventional approaches to characterising wildfire intensity, particularly those based on satellite-derived fire radiative power, remain strongly tied to fire occurrence, making it difficult to distinguish between periods of widespread burning and genuinely anomalous or extreme fire behaviour.Here, we demonstrate that departures from expected relationships between fire detections and energy release reveal increasingly frequent and pronounced episodes of anomalous fire behaviour. These anomalies are characterised not only by elevated total energy release, but by shifts in the upper tail of the fire energy distribution, indicating a growing prevalence of disproportionately intense fire activity. Importantly, this behaviour does not occur uniformly, but instead reflects distinct modes of fire activity, ranging from widespread high-energy burning to more localised, extreme events.Across multiple regions and scales, these patterns point to a broader increase in wildfire volatility, defined by growing variability and instability in fire energy behaviour over time. This suggests that fire regimes are not only intensifying but becoming less predictable and more prone to rapid departures from expected conditions. Within this framework, Mediterranean ecosystems emerge as exhibiting episodic volatility, characterised by punctuated extreme fire activity, underscoring their sensitivity to climate-driven risk.This emerging volatility has important implications for wildfire management under a changing climate. As fire behaviour becomes increasingly unstable, existing assumptions around fire growth, intensity, and spread may become less reliable, complicating forecasting, planning, and response. Recognising and accounting for increasing volatility will be critical for adapting wildfire management strategies to a future in which extreme and anomalous fire behaviour plays a more dominant role.

Contemporary North American wildfires exhibit increasingly erratic intraday burning, posing immediate operational and socioeconomic challenges. Here, we show that climate-driven weakening of day-night (diurnal) weather constraints extends and intensifies burning hours, a key mechanism behind broader fire regime transformations. Analyzing hourly geostationary satellite observations for ~9000 fires (>200 hectares; 2017–2023), we found western mountains and boreal forests experienced the longest active burning hours, with approximately one-third of active days exceeding 12 hours. About 60% of fires reached peak intensity within 24 hours of detection, while 14% of active days peaked at night. On the basis of fire weather, annual potential burning hours were estimated to rise 36% over 1975–2024, with pronounced increases in western regions and spring/fall (48 to 57%). Regions with significant changes gained 26 more potential active days annually and 1.2 additional potential burning hours daily, while extreme days (≥12 or 24 potential burning hours) rose 81 to 233% in fire-prone biomes. Future management requires adaptation to wildfires that increasingly defy diurnal norms.

Background: Vegetation fire risk is increasing in temperate regions like the UK, yet understanding of surface and synoptic weather controls on fire is limited. Aims: We examined seasonal relationships between (i) synoptic weather patterns and surface fire weather, (ii) surface weather and vegetation fire, and (iii) synoptic weather patterns and vegetation fire in England using a comprehensive fire database. Methods: We used ranked percentile curves and relative difference metrics to address our three objectives. Key results: Extreme surface fire weather is predominantly associated with high-pressure systems. The best surface weather predictors of fire are relative humidity (RH), fire weather index (FWI), fine fuel moisture code (FFMC) and initial spread index (ISI). Vegetation fires are strongly associated with high-pressure synoptic weather on the day of, and the week before fires in spring, but much less so in summer. Conclusions: Persistent high-pressure synoptic weather is required to sufficiently elevate surface fire weather for vegetation fires in spring. Summer fires are less dependent on the specific synoptic weather pattern and extreme summer surface fire weather. Implications: Incorporating both synoptic and surface fire weather may help to capture seasonal differences in the drivers of vegetation fire and provide opportunities for longer-term forecasting of elevated fire weather.

Widespread impacts of landscape fire on ecosystems, societies, and the climate system itself have heightened the need to understand the potential future trajectory of fire under continued climate change. However, the complexity of fire makes climate change impact assessment challenging. The climate system influences fire in many ways, including through vegetation, fuel dryness, fire weather, and ignition. Furthermore, fire’s impacts are highly diverse, spanning threats to human and ecological values and beneficial ecosystem and cultural services. Here, we discuss the art and science of projecting climate change impacts on landscape fire. This not only includes how fire, its drivers, and its impacts are modeled, but critically it also includes how projections of the climate system are developed. By raising and discussing these issues, we aim to foster the development of more robust and useful fire projections, help interpret existing assessments, and support society in charting a course toward a sustainable fire future.

Background: Persistent positive anomalies (PPAs) in 500 hPa geopotential heights are an event-based paradigm for tracking large scale atmospheric patterns that often correspond to blocking events. Aims: Examine the importance of PPAs for surface fire weather across the United Kingdom (UK) and vegetation fire occurrence in England. Methods: We used linear regression models and lead-lag statistics to analyse relationships between PPAs and gridded surface weather, and we quantified landcover and season-dependent relationships between PPAs and vegetation fire occurrence and size using a comprehensive fire occurrence database. Key results: Surface fire weather is more extreme under PPAs, characterised by reduced precipitation and anomalously high temperatures. Overall, 34% of England’s burned area occurs during or up to 5 days following the presence of a PPA. The percentage of PPAs associated with vegetation fires increases with increasing fire size, with PPAs being associated with half of fire occurrences >500 ha. Conclusions: PPAs are associated with elevated surface fire weather and vegetation fires. They are especially important for larger fires in heathland/moorland and grasslands. Implications: Synoptic-scale indicators of fire occurrence like PPAs may improve longer-term fire weather forecasts beyond surface fire weather indices alone, aiding vegetation fire preparedness and management decision-making.

Persistent positive anomalies (PPAs) in 500 hPa geopotential height are upper-air circulation patterns associated with surface heatwaves, drought and fuel aridity. We examined the association between PPA events and surface fire weather and burned area at a pan-European level. Europe-wide, extreme fire weather and wildfires were on average 3.5 and 2.3 times more likely to occur concurrently with a PPA, respectively. PPAs were associated with 45% of pan-European area burned between March and October 2001–2021, and there was a latitudinal increase of up to 63% in the percentage of area burned during or up to 7 days following PPAs over Northern Europe. The burned area was highest up to one week following PPA presence, and fuel moisture indices from the Canadian Fire Weather Index System lagged behind peak PPA strength, demonstrating the role of PPAs in pre-drying fuels. Our findings highlight opportunities for developing early warning systems of wildfire danger, having implications for wildfire awareness and preparedness, informing policy and wildfire management decisions like early mobilization and resource sharing initiatives across Europe. This article is part of the theme issue ‘Novel fire regimes under climate changes and human influences: impacts, ecosystem responses and feedbacks’.