Climate change impacts on burn severity in Alaska, Part I: Climate-fire relationships

Unprecedented fire seasons in 2004 and 2005 in interior Alaska raised concerns about the ramifications of climate change for fire regimes in boreal ecosystems. Previous work addressing wildfire-climate relationships in the region has relied on historic area burned and fire occurrence data, both of which have significant known limitations. Burn severity is a better indicator of a fire's immediate and long-term ecological impacts, and captures the spatial variability of these impacts across the landscape. A 23-year burn severity atlas is utilized to test long-held hypotheses that warmer summers are conducive to larger and more severe wildfires in Alaska. Further analyses examine the interrelationship between higher-frequency meteorological parameters and fire size and fire severity. Results confirm that while warmer summer temperatures and extended periods of anomalously warm and dry weather are linked to larger fires, such conditions do not appear to be linked to an increase in the fraction of area burned at higher severity. Although contradictory to conventional wisdom, results show that warmer conditions and extended periods of limited precipitation enable flammability limited fuels to burn, albeit at lower severity, providing greater horizontal fuel continuity that allow for larger wildfires.