A more fiery future for Southcentral?
Some of the weather conditions that led to the destructive McKinley and Swan Lake fires in 2019 could be a mainstay of Southcentral Alaskan summers in the future, according to a new article by a team of EPSCoR Boreal Fires scientists.
Twenty-three researchers – 13 of them core members of the Boreal Fires team - collaborated on “Emerging Anthropogenic Influences on the Southcentral Alaska Temperature and Precipitation Extremes and Related Fires in 2019,” an article recently published online in the journal Land. The researchers studied Southcentral Alaska’s unusual 2019 fire year for signs of human influence on the climatological factors that precipitated the fires, and extrapolated their results out through the coming decades. They found that Southcentral summers are expected to get both hotter and wetter, but that temperature growth will be more pronounced than higher moisture, increasing fire risk.
“The heat is overtaking the moisture,” explained lead author Uma Bhatt, UAF Professor of Atmospheric Science and co-lead of the Boreal Fires component. “Precipitation is going up, but temperature is really going up. The warming is winning out.”
2019 was an unusual summer in Southcentral Alaska: whereas seasonal rains generally quash the fire season by late July, persistent hot and dry weather and high wind events led to a spate of late-season conflagrations, such as the McKinley Fire north of Willow (also the subject of an EPSCoR video) and a resurgent Swan Lake Fire on the Kenai Peninsula. The ongoing fires led to prolonged periods of poor air quality and cost $70 million to suppress.
“Some of the fires, in Swan Lake, for example, they had started in June and had been smoldering,” said Bhatt. “Typically those go out once it starts raining, but it was dry and a few things happened and they just erupted.”
The main purpose of the article was to study whether impacts of human-driven climate change – “the anthropogenic signal” – can be detected in these fires, as it already has been in Interior Alaska. To accomplish this, the researchers studied temperature and precipitation data from both the Susitna Valley and the Kenai Peninsula, and climate model simulations from the National Center for Atmospheric Research Community Earth System Model Large Ensemble (LENS). The scientists quantified fire risk by using the model output to calculate monthly values for the Standardized Precipitation Evapotranspiration Index (SPEI), a measure of surface wetness/dryness and thus flammability.
The team found that 2019 was indeed an extraordinary fire year: it had both the hottest and driest June-August period in Southcentral Alaska in the last 40 years. However, the researchers determined that despite that year’s extreme conditions, the anthropogenic signal has thus far been minimal in Southcentral Alaska: the likelihood of any month’s average SPEI in 1979-2019 being higher than that month’s extreme SPEI in the preindustrial era is still quite small - only around 2 percent depending on the month. This led them to conclude that the anthropogenic signal was not solidly in evidence in 2019.
However, they also calculated values for the years 2040 to 2080, and found a much more pronounced likelihood that average SPEI in any month will rise beyond preindustrial extremes: about 13 percent in June, 9 percent in July and 7 percent in August. These numbers are considerably smaller than those researchers have estimated for the hotter and drier Interior Alaska: an earlier study estimated that the anthropogenic signal has increased the risk of an event like the 2015 Interior Alaska fire season by 34–64 percent. But Bhatt said the Southcentral numbers still indicate a southward progression of human impacts on Alaska’s fire season.
“On the North Slope, we’ve been saying for a long time how human impact, anthropogenic climate change has been visible, and then the 2015 paper showed it was in the Interior,” Bhatt noted. “And now we’re finally getting hints of it farther south.”
Of the researchers involved in the article, 14 are UAF affiliates and 2 are UAA affiliates. The article is part of a special edition of Land entitled “Fire in the Earth System: Humans and Nature.”