Boreal wildfires, particularly in eastern Siberia, have become increasingly frequent in recent decades, causing significant environmental and economic consequences. These fires release substantial amounts of carbon dioxide (CO2) and pollutants into the atmosphere, impacting air quality and contributing to climate change. The interplay between climate and wildfires is complex, with climate change influencing wildfire patterns and wildfires, in turn, affecting the climate system. While factors like heatwaves, drought, and precipitation deficits have been identified as contributing factors, the relative importance of these factors, especially concerning the role of Arctic warming and atmospheric circulation patterns, remains unclear. This study focuses on disentangling the contributions of background Arctic warming (associated with the decline in Russian Arctic sea ice) and internal atmospheric variability (related to Siberian blocking events) to the observed increase in eastern Siberian wildfires. Vapor pressure deficit (VPD), a key meteorological variable reflecting the combined effects of temperature and humidity, is used as a proxy to assess wildfire risk. The research hypothesizes that the declining summer Arctic sea ice and subsequent Arctic warming directly contributes to increased wildfire risk in eastern Siberia via changes in VPD and that internal atmospheric variability, particularly Siberian blocking events, plays a secondary, yet still significant, role.

Previous research has established a clear link between increasing temperatures and reduced precipitation or relative humidity as key drivers of boreal wildfires, particularly in Siberia. Studies have shown significant increases in burned areas and fire-induced CO2 emissions over boreal Eurasia since 2000, with eastern Siberia experiencing a more pronounced increase than western Siberia. The interannual variability of wildfires is also influenced by factors such as atmospheric oscillations (e.g., the Arctic Oscillation) and atmospheric blocking events. The reduced ground moisture associated with enhanced summer warming in the Russian Arctic is also recognized as a contributing factor. While the relationship between Arctic warming and sea-ice decline is well established, the precise contribution of this warming to Siberian wildfires has not been thoroughly investigated. Existing studies haven't definitively quantified the relative influence of Arctic warming linked to sea-ice loss versus internal atmospheric variability in driving the increasing trend of eastern Siberian wildfires. This study seeks to address this knowledge gap by focusing on the role of VPD as a critical indicator of wildfire risk.

This study employed a comprehensive approach utilizing satellite and reanalysis data to quantify the contributions of background Arctic warming and internal atmospheric variability to the recent wildfire risk trend in eastern Siberia. The analysis focused on the period from 2004 to 2021. The researchers used the Fire Weather Index (FWI) from the Copernicus Emergency Management Service for the European Forest Fire Information System (EFFIS) as a measure of wildfire intensity and activity. Sea ice concentration (SIC) data from the Russian Arctic region were used to characterize the extent of sea ice. Background eastern Siberian Arctic warming (BAW) was estimated using summer mean daily surface air temperature (SAT) anomalies from the ERA5 reanalysis data, excluding days influenced by Siberian blocking events (defined using a blocking index based on 500-hPa geopotential height gradients). The vapor pressure deficit (VPD) was calculated using daily mean SAT and dew point temperature from the ERA5 data. To assess the relative contributions of BAW and Siberian blocking events to the increase in VPD, the researchers compared the slope rates of the summer eastern Siberian SAT and VPD time series with and without Siberian blocking events. The study also investigated the characteristics of Siberian blocking events under different SIC conditions, examining aspects such as persistence, zonal scale, movement, decay, and latitudinal location. The study also included analysis of upper ocean heat transport (OHT) near the Barents Sea Opening, to investigate the link between Atlantic warm water inflow and the reduction in Arctic sea ice. Fully coupled climate model simulations (CESM1) were used to examine the relationship between sea-ice loss and summer Arctic warming. Additionally, the Polar Amplification Model Intercomparison Project (PAMIP) ensemble of CMIP6 simulations were used to further validate the findings. Statistical tests, such as the Mann–Kendall test and two-sided student's *t*-test were employed to assess statistical significance.

The study found a significant negative correlation between the summer FWI in eastern Siberia and the Russian Arctic SIC anomaly, particularly strong during 2004–2021. This indicates an intensified link between wildfires and sea ice variability during this period. The summer FWI in eastern Siberia shows a significant upward trend (1.18 standard deviations/decade) over 2004–2021, coinciding with a declining trend in Russian Arctic SIC (−1.04 standard deviations/decade). The analysis of upper OHT near the Barents Sea Opening showed a positive trend over 1979–2018, negatively correlated with the Russian Arctic SIC. This suggests that enhanced ocean heat transport from the Atlantic contributes to Arctic warming and sea-ice decline. The study found that the eastern Siberian Arctic warming exhibits a slope rate of 1.39 standard deviations/decade over 2004–2021. Removing Siberian blocking events reduced this rate to 1.17 standard deviations/decade, indicating that these events contribute to approximately 16% of the warming trend. Importantly, the analysis of VPD revealed a significant positive trend over 2004-2021 (1.70 standard deviations/decade using daily-mean SAT), with the BAW contributing to 79% and Siberian blocking events contributing to 21% of this increase. Using daily maximum SAT, the contributions are approximately 84% and 16%, respectively. Siberian blocking events were found to be more persistent and have larger zonal scales under low SIC conditions, leading to more widespread and intense high-latitude warming and VPD, further enhancing wildfire risk. The reduction in precipitation in eastern Siberia over 2004-2021 is linked to the enhanced BAW and anticyclonic anomaly, exacerbating wildfire conditions. The researchers demonstrate that decreased meridional potential vorticity gradients (PVy) associated with stronger BAW under lower sea-ice conditions contribute to longer-lasting, larger-scale, and slower-decaying Siberian blocking events, further amplifying wildfire risk.

The findings directly address the research question by quantifying the relative contributions of background Arctic warming and atmospheric variability to the increased wildfire risk in eastern Siberia. The strong link between the decline in Russian Arctic sea ice and the increased VPD, a key driver of wildfire activity, is significant. The study highlights the combined impact of both direct Arctic warming and indirect effects through changes in Siberian blocking events. The results emphasize the importance of considering Arctic amplification in the context of Siberian wildfire risk. The study's methodology provides a novel way to separate the impact of Arctic warming from internal atmospheric variability on wildfire trends. This work has broader implications for understanding the impacts of climate change on high-latitude ecosystems and for improving wildfire risk prediction models, especially those incorporating Arctic climate dynamics.

This study demonstrates that the rapid loss of summer Russian Arctic sea ice significantly enhances the risk of recent eastern Siberian high-latitude wildfires. The results show that the background Arctic warming directly caused by sea ice loss is the dominant factor, contributing 79% to the increase in VPD, while changes in Siberian blocking events, influenced by this warming, contribute an additional 21%. Future research should investigate the role of other factors influencing wildfires, such as vegetation type, fuel moisture, and ENSO, while focusing on improving climate models' ability to simulate blocking events and their interactions with wildfire dynamics. Integrated approaches combining satellite data, advanced climate modeling, and machine learning techniques are needed to refine our understanding of these complex interactions.

The study focuses primarily on the trend analysis over 2004-2021, limiting the understanding of interannual variability. The influence of El Niño-Southern Oscillation (ENSO) on Russian blocking activity, although acknowledged, is not explicitly analyzed. The study does not delve into the precise contributions of individual meteorological variables (air temperature, relative humidity, wind speed, precipitation) to wildfire risk because they are interdependent and the VPD itself already effectively captures their combined effects. Further research is needed to fully elucidate the role of wildfire feedbacks, snowmelt, vegetation coverage, peatland burning, frozen soil, and the hydrological cycle on the trends observed in eastern Siberian wildfires. The influence of different tree species on the severity of boreal wildfires is another area requiring further investigation.