Early season lightning storms followed by vapor pressure deficit anomalies contributed to an extreme wildfire season near the high latitude treeline in Northwest Canada in 2014

Abstract:

Fires are the most important landscape disturbance in the boreal forest. Fire location and extent in boreal ecosystems highly depend on ignitions by lightning and periods of high vapor pressure deficit (VPD) that promote the spread of the fires. We show, using fire perimeter and remotely sensed burned area, that during the 2014 fire season, the Northwest Territories in Canada experienced its most severe fire season since the beginning of the fire perimeter record in 1971. Using a pyrogenic carbon consumption model driven by remotely sensed tree cover and burn severity, and meteorological reanalysis data, we estimate total carbon emissions of 136 (SE = 25) Tg for the entire territory. We also found anomalously large fires relatively close (0-300 km) to the high latitude treeline where sparse black spruce forests transition into tundra, ecosystems that are traditionally less affected by fire disturbance. This area received below-average winter precipitation and experienced an early snow melt in 2014. Using data from the Canadian Lightning Detection Network we show that many of these fires were ignited during lightning storms in May and June, and expanded during periods of anomalously high VPD in June and July. Fires that were ignited before July 1 accounted for approximately 76% of the total annual burned area. We hypothesize that the extent and northward expansion of boreal fires, driven by climatic anomalies in lightning and VPD, may accelerate northward species migration with climate change. We also show, using plume heights retrieved from the Multi-angle Imaging Spectroradiometer (MISR), that maximum plume injection heights in 2014 were on average more than 300 m higher compared to observations from other years. These high injection heights combined with the high latitude location of the fires increase the potential for northward long-range transport of black carbon emissions towards Greenland and other vulnerable components of the northern cryosphere.