What limits the growth of lightning fires in the remote northeast Siberian taiga?

In recent years, boreal forests have experienced unprecedented fire activity. These fires have contributed substantially to carbon emissions and posed hazards to human health. In the remote northeast Siberian taiga, the vast majority of fires are ignited by lightning strikes and not by human activity. Furthermore, active fire suppression is largely absent in these remote areas, resulting in uncontrolled fire growth. Here, we present a detailed look at the places and times where these lightning fires do finally stop spreading and aim to identify the causes. We employ various remote sensing and geo-spatial datasets including fire weather as well as landscape variables such as the presence of surface water, road networks, woody fuel load, fire history, elevation and landcover, to pinpoint the limitations to fire growth along fire perimeters recorded between 2012 and 2022 at a 300-meter spatial resolution. We were able to attribute 87% of all fire perimeter locations to a statistically significant (p < 0.01) change in one or more of these fire limitations over either time (fire weather) or space (landscape). The analysis reveals that fire growth is mainly limited by a change in the vegetation (fuel type and fuel load) as well as a change to less favourable weather for fire spread, although there are clear regional differences in the importance of specific limitations. Overall, fire weather seems to be the most important limitation to fire growth in the north of the Siberian taiga where continuous permafrost is present. With a rising frequency of lightning strikes, droughts, and heatwaves in boreal regions, uncontrolled lightning fires have the potential to expand even further in the future, leading to significant implications for vulnerable permafrost landscapes and, consequently, the global carbon cycle.