Unprecedented wildfires in Korea: Historical evidence of increasing wildfire activity due to climate change

In March 2022, three weeks earlier than the usual forest fire season, a wildfire of unprecedented scale broke out in South Korea, spreading rapidly over a large forest area and burning 22,477 hectares in two weeks. This event was likely related to climate change; however, the relevance of climate change in the occurrence of such large fire events is not yet clearly understood. In this study, we assessed how climate change affects the regional climate and the extent to which it enhances the potential risk of wildfires based on the analysis of long-term meteorological observation data from 1923 to 2022 and the calculation of fire weather indices (FWIs). Results showed that the climate regime has shifted from cold and wet to warm and dry winters, with this shift involving a 4 degree celsius increase in temperature, an 8 % decrease in relative humidity, and a 17 mm decrease in precipitation. Dry winter weather has become increasingly severe, resulting in extreme drought in winter 2021 and early spring 2022, with the FWI calculations revealing great potential dangers from fires. However, no major fires were reported in 2021, which is attributable to a reduction in accidental ignition sources owing to the restrictions on human activity caused by the COVID-19 pandemic. This demonstrates the importance of managing artificial ignition. The 2022 wildfires produced substantial quantities of ultrafine aerosols, which consisted mainly of particles smaller than 1.0 mu m. These particles have raised the level of air pollution by more than 20 times compared to before the fires. The CO concentrations were also found to be 4 to 12 times higher than the typical local background concentrations. This study highlights that climate change may make forests more vulnerable to fire in temperate and mid-latitude monsoon-affected regions, where large-scale wildfires were not previously a concern.