The Arctic Oscillation, an atmospheric circulation pattern in the Northern Hemisphere, may boost late winter temperatures in southeastern Siberia, increasing the areas burned by springtime fires, according to a new study published in the Jan. 8 issue of Science Advances.
During the Arctic Oscillation's positive phase, air pressure over the Arctic dips below average while pressure over the northern Pacific and Atlantic Oceans rises, wind patterns change, and warm air masses push northward. The shift may drive temperature increases in southeastern Siberia in February and March, causing snow to melt early in the season and promoting drier conditions poised to spark wildfires come April and May.
Awareness of this one to two-month lag time between the Arctic Oscillation's appearance and spikes in fire activity could help warn local citizens of impending risks, preventing property damage and displacement.
"It would be useful to build local fire policy to prevent enhanced fire risk in the near future," said Jin-Soo Kim, a geoscience researcher at the University of Edinburgh and the first author of the study.
The Arctic stores a precarious trove of greenhouse gases — its permafrost alone is estimated to contain more than twice as much carbon as the atmosphere, while additional carbon is stored within the trunks of evergreen trees. During fire season, when the frozen soil melts and the forests burn, this carbon is released into the atmosphere, contributing to global climate change and adding to the accelerated warming of the polar North.
"The Arctic and pan-Arctic have experienced the strongest warming in the world, the so-called Arctic amplification," said Kim. "[Siberian fires] can cause additional Arctic amplification in the near future."
Fire seasons tend to vary considerably between Central Asia, which mostly experiences agricultural fires near the Black Sea, and southeastern Siberia, which experiences substantial forest fires. Southeastern Siberian fires also tend to vary from season to season and year to year. Although climate phenomena are known to affect fire activity in permafrost regions, scientists have not understood the causes underlying these fluctuations.
To understand why some fire seasons hit the polar permafrost stronger than others, Kim and colleagues analyzed Siberian fire data from a global database for the years 1997 to 2016, collecting data from additional databases and laboratories to estimate atmospheric circulation patterns related to fire activity and to measure monthly surface temperature, precipitation, snow cover and water transfer to the atmosphere.
The researchers confirmed that strong fire activity hardly ever occurs in Siberia without a corresponding peak in the later winter Arctic Oscillation. However, they also determined that local shifts in pressure must be taken into account. They found that an unusual increase in air pressure extending westward from the North Pacific to southeastern Siberia — a separate phenomenon from the Arctic Oscillation — corresponds even more closely with more numerous and faster-spreading fires.
"When we analyzed the large-scale atmospheric pattern using the interannual variability of burned area over southeastern Siberia, an Arctic Oscillation-like pattern comes out, but it's not exactly the same," said Kim. "Actually, high pressure pattern over southeastern Siberia shows an even closer relationship with interannual fire activity variability.
While future shifts in the Arctic Oscillation remain uncertain, Kim explained that this and other naturally varying atmospheric patterns are far from the only factors driving Siberian wildfires.
"Regardless of the Arctic Oscillation, ongoing Arctic warming due to greenhouse gas increases may cause earlier snow melting and it can contribute to extension of fire season length," said Kim. "I also believe that fire activity is not only proportional to climate but also ignitions by human activity."
Kim noted that although eastern Russia and northeastern China experienced similar climate anomalies in 2003, Russia experienced record-breaking fires while China's were significantly less damaging, suggesting the importance of fire management strategies during times of heightened fire risk.
As part of the UK Space Agency-supported Forests 2020 project, Kim and colleagues are mapping fire risk and related carbon emissions driven by another climate pattern, the El Niño Southern Oscillation, in the pan-tropical forests of Indonesia and the Amazon.