Northern Forests Increasingly Getting Burned

A look at the history of forest fires and drought in Canada and Alaska finds three striking trends emerging over forty years.

Between 1959 and 1999 the annual number of large wildfires generally increased, the area burned expanded, and the proportion of Canada and Alaska experiencing drought grew.

Altogether during the four decades 13% of the forests was burned by large fires, amounting to 840,000 square kilometres. Hardest hit were northern Saskatchewan, Manitoba and western Ontario. Even though this study only assessed 3% of the forest fires in Canada, it examined all fires over 200 hectares that together accounted for 97% of the land area burned.

Researchers from Purdue University in West Lafayette, Indiana, found that the years when many fires became wide-spread infernos coincided with years of extensive dry conditions. The relationship between drought and wildfire was exponential. The amount of forest burned during a summer across northern North America grew exponentially as the area affected by drought increased. The biggest fire season occurred in 1989 when 759 large wildfires raged and 57% of the region had unusually dry weather.

Droughts arose from exceptionally high temperatures or low precipitation or both during May to September. The extent and locations of drought across Canada and Alaska varied from year to year. Wildfire outbreaks concentrated in the areas experiencing summer drought.

Overall, the trend in recent decades to higher temperatures and associated drought is linked to climate change. Dryer than normal conditions were also brought about by shifts in large-scale ocean circulation patterns, including the Pacific Decadal Oscillation (PDO), El Niņo Southern Oscillation (ENSO) and Arctic Oscillation (AO).

Reference

Jingfeng Xiao and Qianlai Zhuang. 2007. Drought effects on large fire activity in Canadian and Alaskan forests. Environmental Research Letters. 2: 044003.

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