Fire-induced surface forcing of the Siberian larch forests since 2000 in the context of climate change

The Siberian larch forests are a major component of the global boreal biome with wildfire being the most important disturbance agent. However, due to their unique characteristics and remote location, coupled with a limited record of remotely sensed datasets, we know little about the post-fire albedo dynamics in the region as well as the associated climatic impact, especially over a relatively longer temporal span at the regional scale. This is unfortunate as it has been suggested that the fire-induced albedo changes may have a pivotal role in controlling the net climatic impact of the boreal forests. Utilizing a 30-m 24-year stand age distribution map of the Siberian larch forests, combined with the full record of the MODIS albedo product, this study quantified the surface forcing induced by stand-replacing fires in the Siberian larch forests over 2001-2015. The results show that the larch forests experienced stand-replacing fires in the region has a cooling effect lasting for more than 25 years, and the magnitude of the cooling (-9.60 ± 0.03 Wm-2) is much larger than previously expected. Due to the strong cooling of stand-replacing fires, coupled with their wide distribution, the net surface forcing of the Siberian larch forests between 2001 and 2013 is negative (-0.78 Wm-2). In contrast, the forests that did not experience stand-replacing fires since 2000 show a warming effect, which is largely attributable to a lengthening of snow-free duration in the region. These results together indicate that wildfire may play a much bigger role in modulating the climatic impact of the Siberian larch forests than we previously thought, but this role is likely weakened by the considerable warming in the region, thus needs to be evaluated in the context of global climate change.