The 2023 Canadian wildfire season stands as a stark reminder of the escalating threat posed by wildfires, driven by a complex interplay of climate change and human influences. This year witnessed an unparalleled scale of fire activity, far exceeding historical averages and resulting in substantial ecological and societal consequences. The research question guiding this study is to understand the contributing factors to this record-breaking fire season, specifically focusing on the role of extreme weather, pre-existing landscape conditions, and their combined effect on fire size and duration. The purpose is to provide a comprehensive analysis of the 2023 Canadian wildfire season, offering insights into the mechanisms driving its exceptional severity and informing future fire management strategies. The importance of this study stems from the need to improve our understanding of wildfire dynamics in a changing climate and to develop effective mitigation and adaptation strategies to minimize future risks to both ecosystems and human populations. Understanding the intricate interplay between climate-driven extreme weather events, landscape legacies, and human interventions is crucial to forecasting future fire risk and developing effective strategies for prevention, response, and post-fire recovery. The 2023 season serves as a critical case study to achieve this understanding, offering invaluable data to inform future research and policy decisions.

Previous research has established a clear link between climate change and increased wildfire activity globally. Studies have shown that rising temperatures, altered precipitation patterns, and changes in snowmelt timing contribute to longer fire seasons and more intense fire weather conditions. In Canada, numerous studies have documented these trends, particularly focusing on the western provinces. However, the 2023 season presented an unprecedented challenge, extending far beyond typical regional patterns. The literature also reveals the critical role of landscape legacies, such as past logging practices, forest age distribution, and prior fire events, in shaping fire behavior and susceptibility. The interaction between these human-influenced landscape legacies and climate-driven changes is a key area of ongoing investigation, with a growing body of work indicating their synergistic effects on fire risk. While previous studies have highlighted the societal impacts of wildfires, including evacuations and air quality degradation, the magnitude of these impacts during the 2023 season presented a unique opportunity to analyze the extent of these ramifications across a national scale.

This study employed a comprehensive approach using multiple datasets to investigate the 2023 Canadian wildfire season. A hybrid fire perimeter dataset (NBAC-M3) was generated by combining data from the National Burned Area Composite (NBAC) and M3 (MODIS Burned Area) perimeters, providing a near-complete picture of the area burned. Daily fire growth was estimated by interpolating fire detection dates from hotspots using ordinary kriging. Snowmelt timing was determined using data from the Interactive Multi-sensor Snow and Ice Mapping System, while drought conditions were assessed using root zone soil moisture data from the Global Land Data Assimilation System (GLDAS-2.2). Weather and fire weather data were obtained from the ERA5 reanalysis, including temperature, precipitation, vapor pressure deficit (VPD), and the Canadian Forest Fire Weather Index (FWI). The extent of extreme fire weather was defined as the forested area exceeding the 95th percentile of FWI values (FWI95) between 1991-2020. To examine large-scale atmospheric patterns, an algorithm was applied to identify atmospheric blocking events using 500-hPa geopotential heights. Air quality was analyzed using PM2.5 concentration maps from Environment and Climate Change Canada's (ECCC) Regional Air Quality Deterministic Prediction System-FireWork. Evacuation data for Canada from 1980-2023 were obtained from the Canadian Wildland Fire Evacuation Database. Statistical analyses, including correlations and comparisons with historical data, were conducted to understand the relationships between different variables and the observed fire activity. The proportion of various land cover types burned was calculated by intersecting the NBAC-M3 dataset with SCANFI (Spatializing Canadian National Forest Inventory) classified land cover raster datasets. The researchers used a combination of statistical modeling and spatial analysis techniques to examine the interactions between various climatic factors and the resulting fire behaviour.

The 2023 Canadian wildfire season burned approximately 15 million hectares, significantly exceeding the 1986-2022 average. This unprecedented area burned was largely attributed to the record number of large fires (>200 ha) and, particularly, very large fires (>50,000 ha). The number of very large fires in 2023 (60) was considerably higher than the historical average (7), and these fires accounted for 73% of the total area burned, compared to a historical average of 41%. The study found a strong correlation between fire size and the number of days with extreme fire weather (FWI > FWI95). The median duration of very large fires in western Canada (82 days) was significantly longer than in eastern Canada (40 days), potentially linked to the longer duration of extreme fire weather. Analysis of snowmelt timing revealed earlier snowmelt in 2023 compared to the 2004-2022 average, contributing to earlier drying of root zone soil moisture (RZSM). This was followed by a record maximum RZSM drying amount in many regions, setting the stage for heightened fire risk. The 2023 fire season also saw record levels of May and June drought, further exacerbating conditions. Anomalies in temperature, precipitation, and vapor pressure deficit (VPD) during the fire season (May 1–October 31) were significantly higher in 2023 than in the 1991–2020 baseline period, ranking exceptionally high compared to data available from 1940. The frequency of atmospheric blocking events was substantially higher in 2023 than the 1991–2020 average, contributing to sustained extreme fire weather conditions. The analysis showed a strong relationship between persistent positive anomalies in 500-hPa geopotential heights (a proxy for atmospheric blocking) and the extensive area burned. Widespread air quality alerts were issued across North America due to the pervasive wildfire smoke, significantly impacting human health and visibility. The large area burned in 2023 also had profound ecological impacts. A significant portion of young forests (<30 years old) burned, raising concerns about post-fire tree regeneration failures and potential shifts in forest ecosystem processes. The large-scale burning of young forests could further impact forest productivity, carbon storage, and biodiversity, challenging the resilience of forest ecosystems.

The findings of this study strongly support the hypothesis that the 2023 Canadian wildfire season was a result of the convergence of extreme weather events, prolonged drought, and pre-existing landscape conditions. The unprecedented scale of the 2023 fire season underscores the need for adapting to a changing climate characterized by more frequent and intense extreme events. The significant contribution of very large fires to the total area burned highlights the importance of long-term fire weather conditions in determining fire size and duration, especially in a context of already dry conditions and earlier snowmelt. The longer duration of extreme fire weather in western Canada compared to eastern Canada is also a notable finding, highlighting geographic variations in fire risk. The results emphasize the critical interplay between climate-driven changes in snowmelt and soil moisture dynamics, highlighting the importance of considering these factors in fire risk assessments. The severe air quality issues highlight the far-reaching impacts of wildfires, emphasizing the need for robust early warning systems and public health strategies. The large-scale burning of young forests underscores the complex ecological ramifications of these events and their potential long-term effects on forest regeneration and biodiversity. This study highlights the pressing need for adapting to a changing climate characterized by more frequent and intense extreme events, improved forest management, and stronger collaborative efforts to manage wildfire risks effectively.

The 2023 Canadian wildfire season stands as a stark illustration of the significant challenges posed by climate change and landscape legacies. The study concludes that the record-breaking fire activity resulted from a confluence of factors including extreme weather conditions, unprecedented drought, early snowmelt, and persistent atmospheric blocking events. This emphasizes the need for integrating climate projections into long-term fire management strategies. Future research should focus on more precisely quantifying the relative contributions of climate change and human-induced landscape alterations in shaping future wildfire risks. Further refinement of fire behavior modeling to account for the combined effects of climate variability and landscape legacies is crucial. This necessitates improving our understanding of the interaction between extreme weather, drought, and forest resilience. Finally, enhancing early warning systems and improving public preparedness are crucial to minimizing the societal and economic consequences of these events.

While this study offers a comprehensive analysis of the 2023 Canadian wildfire season, some limitations should be noted. The analysis relies on existing datasets, which may have inherent uncertainties and limitations in spatial and temporal resolution. Specifically, the accuracy of the hybrid fire perimeter dataset depends on the accuracy of both NBAC and M3 data. Additionally, disentangling the relative contributions of climate change and human land use legacies is challenging, necessitating further research. While the study considers a variety of factors, other factors could contribute to the unprecedented fire activity. Finally, future research is needed to further investigate the long-term impacts of the 2023 fire season on ecological processes, forest regeneration, and biodiversity.