# Wildfires in the Siberian Arctic
## 4 Discussion  
### Changes in Wildfire Dynamics for the Siberian Arctic  
Wildfire severity in the Siberian Arctic greatly increased in the first two decades of the 21 st century. From the 2001-2010 to the 2011-2021 period, wildfire frequency increased by a factor of about 3, accompanied by a doubling of the extent of the area burnt. This increase in frequency and areal extent is consistent with the pattern of increased wildfire in the Siberian taiga since the 1990s [41] and in the tundra of Alaska and Canada [42; 43]. We report here that annual fire frequency and extent of burnt area in the Siberian Arctic was more strongly correlated with ground moisture content (rho = \(-0.82\) and \(-0.76\), respectively) than with precipitation (rho = \(-0.56\) and \(-0.49\), respectively). In this region, ground moisture is gained through precipitation and stored as ice in the frozen permafrost. We suggest that this pattern of greater sensitivity may be due to release of soil water from thawing permafrost. Results presented here suggest that this increase in wildfire frequency and extent is likely due to the combination of a greater land area potentially subjected to fire due to dryer ground cover, i.e., a longer fire season, and increased sources of ignition. All of those factors are driven by present climate trends. The positive correlation to growing season temperature is likely due to the indirect effects of temperature on fuel quality, particularly moisture content. Extreme shifts in the fire boundary were synchronized with air temperature and drought index SPEI anomalies (\"heat waves\"). Earlier fire boundary advance was noted on the Yamal Peninsula of Western Siberia [7]. We found that that the seasonal distribution of the wildfires in the extreme years turns from typical for high latitudes unimodal pattern to the bimodal pattern that is typical for the lower latitudes [41]. The increased frequency and extent of wildfire will likely accelerate the northward migration of the taiga-tundra boundary [10]. Burnt tundra reduces competition from fire-sensitive grass and moss/lichen communities and provides opportunities for shrub and tree settlement by pioneer trees species (e.g., larch, birch, and alder) [15]. Migration of bushy shrubs and larch into former tundra has been described for the Yamal peninsula (Western Siberia) and the Anabar Plateau (Eastern Siberia) [9; 44; 45]. Figure 5: Gross primary productivity (GPP) post-fire trends within “hot spots”. GPP increasing and decreasing trends observed within 97.3% and 2.7% of “hotspots”, correspondingly. Trends significant at \(p<0.05\). Note: hot spots presented as a non-scale points. The northward migration of the northern limit or boundary of wildfire occurrence in WS has both quantitative and qualitative effects. The additional land area apparently subject to fire would be expected to result in an increased number of fires. Meanwhile, previous research estimated that the fire return interval (the time period between consecutive stand-replacing fires) at the northernmost larch forest boundary in Siberia may reach 300 yrs. [46]. Additionally, the northward migration subjects a greater proportion of Arctic tundra as well as taiga to wildfire. The duration of the fire season in the continental climate of WS increased by more than a month and was correlated to growing season temperature which in turn increased the flammability of potential fuel. The decreased duration of the fire season in FE was correlated to increased moisture in the ground cover, resulting in decreased flammability of potential fuel. Our analysis indicates that lightning strike frequency explained 6-8% of the year-to-year variation in wildfire frequency. Lightning strikes are the primary source of wildfire ignition in this region [3]. Lightning is especially efficient in causing ignition during \"dry thunderstorms\" that yield little or no precipitation [47]. Low ground moisture content driven by warming conditions in the Arctic increase the likelihood that a given lightning strike will result in wildfire.