Why is the Alaska fire season so quiet this year while Canada has major wildfires? Alaska climatologist Rick Thoman attributes the lack of fires in Alaska (only 934 acres burned by the end of June) to a lack of lightning as well as cooler, moister weather this year (Alaska June 2023 Sea Ice and Wildfire). Interesting that this year Alaska retained a lot more sea ice in the Chukchi sea and Arctic Ocean above Barrow: there is some evidence linking regional climate to sea ice concentration (Zou, et al. 2021). Meanwhile, Canada is breaking records with 22.7 million acres burned (9.2 million ha) as of July 9. CiFC (https://ciffc.ca/) reports 3,678 fires spread across the entire country. Canadian and US cities (including Detroit, Pittsburgh, and Chicago) have been suffering poor air quality for much of the mid-summer with little relief in site. Is there an explanation for the unusual pattern? The global temperature anomaly for May (figure) may be one clue. Strong linkages have been found between warm temperatures and wildfire activity, mainly because of accelerated drying of vegetation fuels. In the western US, Abatzoglou and Williams (2016) found that human-caused climate change caused over half of the documented increases in fuel aridity since the 1970s and doubled the cumulative forest fire area since 1984. At any rate, 2023 brought very little snow to eastern Canada, so it melted early and Fire Weather Indices have been unusually high.

Fire regime is changing in other parts of the world. Rebecca Scholten is finishing up a PhD in Amsterdam studying weather patterns which correlate with fire activity around the north, especially arctic areas. She’s noted that changes in the polar jet stream driven by warming global temperature seem to be correlated with more wildfire in northern tundra ecosystems. A simplified explanation would be that a “wobbly” polar jet stream caused by weaker cold sink over the Arctic can mean calming in mid-latitudes but intense heat domes, dry and windy conditions, and more convection over high northern latitudes. There seems to be a strong link with these conditions and the Siberian megafires in 2019-2021. Her recent paper in Science points to accelerating changes in high latitudes with earlier snowmelt and a tripling in the frequency of this “Arctic front jet pattern.” Curiously, when this pattern sets up, it may moderate conditions–at least with respect to winds–over interior Alaska!

Citations:

Zou, et al 2021. Increasing large wildfires over the western United States linked to diminishing sea ice in the Arctic. Nat Commun 12, 6048. https://doi.org/10.1038/s41467-021-26232-9

Abatzoglou and Williams. 2016. Impact of anthropogenic climate change on wildfire across western US forests. PNAS 113 (42) 11770-11775. https://doi.org/10.1073/pnas.1607171113

Scholten, R.C. et al. 2022. Early snowmelt and polar jet dynamics co-influence recent extreme Siberian fire seasons. Science 378, 1005–1009. https://doi.org/10.1126/science.abn4419